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tiptop
06-12-2008, 08:13 PM
It's been a while since I posted, been a little busy getting ready for class. Anyhow I stopped by my friends diesel shop on the way home today and found six nice wrist pins. They measure 5.25 tall, 2.375 od and a hole size of 1.125;
I checked them with my best square and they look right on. I will do a better evaluation when I get more time. In the mean time here are some pics. They are in my album at this location.

http://imageevent.com/aatiptop/toolspage/miscellaneoustools?n=0

Edited od measurement.

johnhurd
06-12-2008, 08:31 PM
Must be a optical illusion that material looks thicker than .150 to me

Chipslinger
06-12-2008, 08:37 PM
It's been a while since I posted, been a little busy getting ready for class. Anyhow I stopped by my friends diesel shop on the way home today and found six nice wrist pins. They measure 5.25 tall, 1.375 od and a hole size of 1.125;
I checked them with my best square and they look right on. I will do a better evaluation when I get more time. In the mean time here are some pics. They are in my album at this location.

http://imageevent.com/aatiptop/toolspage/miscellaneoustools?n=0

In reference to your Sig line, How is adrian doing?

Lew Hartswick
06-12-2008, 11:01 PM
In reference to your Sig line, How is adrian doing?
Not Chipslinger but I check his BB once a day and he has been on his
boat a lot. pix of his kid etc.
...lew...

lugnut
06-12-2008, 11:32 PM
John, I get .625 thick:) your eyes don't lie, just your math:D
Jay I think they would make great cylinder type squares. Looks like a great find.
Mel

tiptop
06-12-2008, 11:37 PM
Mel, John was right, I had my numbers wrong. I went back and edited my original post instead of reposting. Yes i think they will work good. If they are off, I guess it would give me a reason to get the cylindrical grinder up and running. Jay

Forrest Addy
06-13-2008, 12:00 AM
Wrist pins make good culinder squares if the ends are ground referencing from the OD. If you have a granite flat, a dial test indicator, and a dial test indicator you can check the actual squareness to as close as you can read the DTI. And no you don't set the gage from from a hard square. Squares are self checking if you know the trick.

For not enough to buy a coffee and brag rights lasting until your next aw-$hit, what it the surface gage trick for proving a square?

TGTool
06-13-2008, 12:38 AM
Ah yes, nice trick. This came up awhile back so I'll let someone else go for the coffee this time.

Jan

dave5605
06-13-2008, 05:20 PM
I could make a real nice ring roller with those wrist pins.

tiptop
06-13-2008, 07:18 PM
Forrest, I have to confess that after my hour long search, I have not come up with a better way to check a cylindrical type square. Now I know (and Have for years) how to check and set a carpenters square (since I was schooled as a pattern maker) but I do not know of a precise way to check a machinists square against itself. I do understand the game of threes and checking agaist each other. I am sure that the weekend after next you can enlighten me and 16 or 17 others. I can hardly wait. Unfortunately I am one of the home shop types that want to repair old broken down antique machine tools. This is what I like about my machine work and being semi-retired, I can do what I like and never make a dime and be happy just trying.
Yes dave5605, they would make a really nice ring roller, but I have one in progress already so I think I will continue with my origanal thought.

Paul Alciatore
06-14-2008, 02:41 PM
The only method I know for self-checking a square is to place it against a straight edge and scribe a line with it. Then reverse it and scribe another line starting at the same point. If the lines diverge, the square is off.

But this method is not going to give you tenths, perhaps only accurate to a few thousanths. And it is limited by the straightness of the straight edge and the width of the area available for scribing the lines.

I am sure they can be compared with blocks or cylinders, but that is not self checking.

Paul Alciatore
06-14-2008, 02:50 PM
OK, here is another way to check a square. Place the faceplate on the lathe. Place the square against the faceplate. Run the DI along the edge of the square using the longitudal feed on the lathe.

Now, rotate the faceplate and square 180 degrees, keeping the square in exactly the same position on the faceplate. Now run the DI along the SAME edge of the square.

The readings should all be zero, but that will not always be the case. If the readings match for each point along the square's edge then the square is good. Any differences will indicate an out of square condition. Remember that all readings must be taken in the same direction or sense. The DI will be reversed on the second pass so it may be necessary to reverse the readings on the second pass. Think front-to-rear = increased reading for both. Or rear-to-front for both.

Looking for matched readings will allow for any misalignment in the lathe spindle axis vs the ways.

But again, this is not self checking as you are using the lathe.

lazlo
06-14-2008, 03:31 PM
The only method I know for self-checking a square is to place it against a straight edge and scribe a line with it.

To check a cylindrical square:


Mount it on your mill table, and put a DTI in a Zero-Set holder in the spindle.

Find the tangent at the bottom of the cylinder on one edge of the square by feeding the saddle in and out and finding the high spot.

Preload the DTI, and wind the spindle/DTI from the bottom to the top. Measure the difference.

Without touching the cylindrical square, spin the indicator holder to the opposite site (180 from where you were), find the high spot again and wind the spindle/DTI from the bottom to the top. Measure the difference.

Now rotate the DTI holder 180 (back to where it was), rotate the cylinder 1/2 a turn and repeat the process.


From those three measurements, you can calculate the taper and lean of the cylindrical square with simple trig.

I scratch those numbers on the top of the cylindrical square, so I always know what I'm working with...

Forrest Addy
06-14-2008, 07:51 PM
First of all I apologise for hijacking the thread but it seemed like a good opportunity to pass on some relevent info.

Here's how to prove a square.

Squares are self checking; you can use them to check themselves. The ways to do so come down to us from old metrology books and apprentice texts. It's old technology. An old fart taught me this particular trick back when and I've passed it on many times since then.

You need cylindrical square to test, a surface plate, a surface gage, and a dial test indicator (and clamps etc).

Naturally you have work clean and control heat input to the equipment.

The mast of the surface gage has a ball on it. Invert the mast so the ball is placed into into the "crotch" of the base barely clear of the surface plate so the mast inclined back at some angle that you will have to adjust to bring the DTI into position.

Mount the DTI on the upper part of the mast and adjust so the indicator ball is in a vertical plane over the mast ball and contacts the square under test just below the upper corner of the reference diameter.

Youve just made a gage. Bring the assembled surface gage to the square under test and contact the ball to the reference diameter. Adjust the DTI to a good zero.

With the assembled gage in contact with the square under test rotate the surface gage around a vertical axis a few degrees either way to maximize the reading. Refine the zero. This will take some careful fiddling. Be careful: the merest knock or nudge may disturb the setting.

Move to the opposite side of the square and take a reading rotating the gage to maxiimize DTI reading. Note any error. Return to the original side to check for repeat zero. If readings are equal on both sides of the square and you have determined by precious checks the square is a near perfect cylinder then the base of the square is perpencidular to the reference cylinder. The principle derives from the Euclidean proposition defining a cylinder as a rectangle rotated around one edge. The buisness with thesurfaceplate, surface gage, DTI etc takes advantage of it to quantify the truth of the square.

This procedure doubles the acual error so it is very accurate if well executed. If your indicator is in good shape and your readings are consistent, you can prove and quantify (if the cosine error is accounted for) to 1/10 the DTI's graduations. Check the square at a number of locations and make repeat zero checks between each. While the surface gage is set up check every square you own and make record of the error thus calibrating and proving what may have been mystery tooling to date.

This is sensitive work but well within the capability of a home shop owner exercising ordinary care.

lazlo
06-14-2008, 09:59 PM
Hi Forrest,


With the assembled gage in contact with the square under test rotate the surface gage around a vertical axis a few degrees either way to maximize the reading. Refine the zero. This will take some careful fiddling. Be careful: the merest knock or nudge may disturb the setting.

Move to the opposite side of the square and take a reading rotating the gage to maxiimize DTI reading. Note any error. Return to the original side to check for repeat zero.

That's the process I described in the post above yours, which is basically a slightly more detailed version of Paul's second post (with an extra reading added to measure the lean) :)

If you use that method to take three readings that are spaced 90 apart, you can derive the taper and lean of the cylindrical gage. Say the first measurement was D1, and the second measurement 180 opposite was D2:

Taper = (D1 + D2) / 2

Now the third reading, with the cylinder rotated and the DTI back at the start is D3:

Lean = [(D2 - Taper) - (D3 - Taper)] / 2

Cheers,

Robert

tiptop
06-14-2008, 11:05 PM
I am enjoying this thread, now if I could see the top of my bench to lay some tools out, I would try some of your combined wisdoms. I believe the first test for a used wrist pin should be, to see if it is still round and then not hour glass shaped from wear. So I will be thinking about this for a while as I am to busy to clean up now. Thanks for the input, Jay

oldtiffie
06-14-2008, 11:45 PM
OK.

All the previous posts seem to assume/presume that the wrist pins are new, in pristine condition, are round and straight and neither tapered nor worn.

They also seem to assume that the ends are flat and that if tapered that only the outer diameter is touching the test table. If the taper is such that the "high" part is near or at the centre (ie near the central hole) the "square" will be more likely to "rock" (on its end/s).

I would put those wrist pins on a good vee-block and put a good dial indicator on the wrist pin.

First, to check for "round", I'd spin the pin and see that there is no deviation of the dial indicator at several points along its length. The next test would be for straightness. I'd move the pin along the stationary vee-block and under the stationary indicator (without rotating the pin in the process). I'd do that at least at 4 points/lines 90 degree apart and check that there was no deviation on the indicator.

Now, no matter what method is used this far, the main problem is to get the ends machined such that they are "square" to the cylinder face and axis, and preferably with only a narrow (say 1/8") "land" on the outer edges of the end faces with the "relief" to minimise picking up and grit etc. Whether or not this machining is done on a lathe or surface or cylindrical grinder is of no consequence so long as the required outcome is required.

The best or optimum result is achieved with a maximum "end diameter" to "length of cylinder" ratio and with the minimum practical width of the "land" on the end face/s.

I would never use a machine slide to check for this order of accuracy unless I was assured that the machines slides were very accurately "squared" to each other. Further, even on a perfectly squared machine, the clamping can have quite an effect which may cause an indicator to show an error on the "pin" when in fact it is in the machine. (This applies to mills and lathes).

This is the reason I bought my Machinist's Frame Level which is accurate (well the certificate says it is and so far I've had no reason to doubt it) to 0.02mm/meter = 1:50,000 for flat and square.

http://i200.photobucket.com/albums/aa294/oldtiffie/Squaring-up/Machinist_Square1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Squaring-up/Machinist_Square2.jpg

When I put my "new" (cylindrical) squares on both the mill table - and as a check on the magnetic chuck - on my surface grinder - and put a "Class 1" machinists square on them and there was no discernible change in the (very narrow) "gap"/"line of light" with a strong lamp in the back-ground. The same result applied when I put any two "squares" against each other, then rotated first one and the the other 90 degree against each other and then "end for ended" each in turn and tried one against the other. Same result - every time.

The human eye has an extra-ordinary ability to see very narrow gaps using light and even better to see any change in light "width" variation which may indicate taper or lack of straightness. This is in the order of a "tenth" or so.

Some may recall my thread on these tubular squares that I made and used to "true-up" my angle plates. After milling those angle plates I placed my "Class 1" test square on them as well as my (tubular) machine squares and there was no discernible variation of gaps. As a check of an against my Machinists Frame Square, I repeated the tests using it and it was as good as I could wish for:
http://i200.photobucket.com/albums/aa294/oldtiffie/Squaring-up/Squaring1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Squaring-up/Squaring4.jpg

lazlo
06-15-2008, 12:49 AM
I would never use a machine slide to check for this order of accuracy unless I was assured that the machines slides were very accurately "squared" to each other. Further, even on a perfectly squared machine, the clamping can have quite an effect which may cause an indicator to show an error on the "pin" when in fact it is in the machine. (This applies to mills and lathes).

Tiffie, I didn't make up the method I described -- it's textbook (Moltrecht).

The machine ways don't come into play because they're not moving while you're measuring the cylinder. And the spindle runout doesn't matter because you're measuring on opposite sides, and adding the errors.

But if you're really worried about it, then use Forrest's spin on the technique, where you make the same measurements with the DTI on a surface gage on a surface plate.

In either case, you'll get much more accurate values than eyeballing it. More specifically, you get discrete values for the cylinder's taper and lean. Once you know those values, you can subtract out the error when you're using the cylinder, for super-precise work (like machining an angle plate)...

oldtiffie
06-15-2008, 02:14 AM
A couple more comments are in order here.

First of all, it is not best practice to be moving the indicator/surface guage etc. relative to the work under test as errors can creep in. It is best to move the work under or relative to the indicator and any aids or fixtures, tools etc. that may be used in the process.

If the base of the surface guage is (very) flat that will be better. But an error in either or both the base of the surface guage and the surface plate will be magnified at the highest point of the indicator on the surface guage mast and will be (falsely) indicated (as) less at the lower point of measurement - the relevant ratio is the length of the base of the surface guage in contact with the surface plate to the height of the indicator above the surface plate. If there are any errors - no matter how small - as regards "flatness" of the surface plate between any two or more positions of the surface guage on the surface plate it will be manifested at the indicator position/s and will or may give a "false positive/negative".

"Tapers" as such should be pretty well a non-issue in most cases if the cylinder is sufficiently round, parallel and straight.

It is quite possible and probable that even if the two ends of the cylinder are "flat" that they may not be parallel to each other in which case different "readings/results" may apply to each end of the "square" and must be marked and recorded as such unless only one end is designated for and used as a "square" reference/tool for further work.

My objective was to achieve "squares" that are accurate to my requirements such that they can be used "as is" without further "adjustment" or "allowance/s" (for) as a (pre)condition for use.

I deliberately used methods that would compound my errors with the intent of finding and identifying those errors. I am satisfied with the outcomes. Others may not be as is their indisputable and undisputed and respected right.

I am not much fussed either by "Co-Sine errors" as an indicator is just that - an indicator - and for accurate indicating where a specific quantity is required, should be used in conjunction with a "reference" such as a known size or "slip guages" etc. Ideally the axis of the indicator arm should be parallel to the (in this case) axis of the cylindrical "square" under test.

The potential or real "Co-Sine errors" need to be put into perspective. I suspect that there is a lot of "(over??) hype" with this as while it is certainly applicable in some circumstances, it may not be applicable in all of them. I seem to hear it as a "mantra" when it may not need to be (perhaps its just my hearing).

It is the difference between the "base" and the "opposite side" in triangular geometry and trigonometry. Some examples for "unit" ie "1" length of "base" with respect to opposite side/s" are:
- 5 arc degree: 0.9962 ~ 3.8 per 1,000;
- 10 arc degree: 0.9848 ~ 15.2 per 1,000; and
- 15 arc degree: 0.9659 ~ 34.1 per 1,000

I accept that it will be of concern to others and that they may act as they like - as can I.

As I've said often enough, I have no dispute with "Reference Texts" to the extent that what they say is correct. But I am not going to take them as "Gospel" or as "the one true Bible" etc. I want to know not just what they say but the logic and end-results required of and achievable by them.

That there are often so many held in such high esteem but use different methods to achieve generally similar end-results supports my opinion. I do not like "prescriptive" methods which lean toward the "You must do it this/my way - there is no other" way of "leaning" on the reader.

I have no use for "Machining"-type/related "Evangelists", "Hot Gospelers" or "Catechisms" or the like in my shop - or in my life either.

I have absolutely no problem with anyone (me included at times) using any or all of those prescribed methods conditional on my being able to do it differently to get a result that suits me.

lazlo
06-15-2008, 09:25 AM
"Tapers" as such should be pretty well a non-issue in most cases if the cylinder is sufficiently round, parallel and straight.

LOL Tiffie! That the whole point of this thread! The OP found some wrist pins, and he's asking how to measure their accuracy.

The measurement techniques that Paul, Forrest and I posted are ways to measure whether the cylinder is round and straight -- also known as the Taper and Lean :D


I have no use for "Machining"-type/related "Evangelists", "Hot Gospelers" or "Catechisms" or the like in my shop - or in my life either.

Then get back in the shop and Get 'R Done Mick :)

oldtiffie
06-16-2008, 05:11 AM
"Tapers" as such should be pretty well a non-issue in most cases if the cylinder is sufficiently round, parallel and straight.


LOL Tiffie! That the whole point of this thread! The OP found some wrist pins, and he's asking how to measure their accuracy.

The measurement techniques that Paul, Forrest and I posted are ways to measure whether the cylinder is round and straight -- also known as the Taper and Lean :D



I have no use for "Machining"-type/related "Evangelists", "Hot Gospelers" or "Catechisms" or the like in my shop - or in my life either.

Then get back in the shop and Get 'R Done Mick :)

Well, lazlo as I am such a nice chap, I will give you some "wriggle room".

Now having been back to my shop as ordered for Penance and Enlightenment (but no Absolution), and "got 'er done" and I return bringing news and glad tidings - and more "info".

It seemed to me that all of you just jumped in assuming the wrist-pins were accurately round, straight and parallel - or perhaps you forgot to mention it.

I checked it first.

Just shown me what I missed and why my method doesn't work as I think it does and within the resources available to me in what is an average HSM shop - it works.

I checked every square against another to ensure that I compounded any errors to make sure that I found them (which I didn't) so that I could correct them if needs be (which I didn't have to).

I thought I'd chase up some more info on this matter of "Master Squares" and checking try-squares.

I know you will be interested and grateful - so here goes.

First of all, I will deal with the testing of a try-square.

There are are two methods which I learned both in the Main Work-shops and the Tool-Room, the first of which is a self-centering method using Tool-makers "buttons" - which is what I thought Forrest was talking about:
http://i200.photobucket.com/albums/aa294/oldtiffie/Squaring-up/Trying_a_try_square1.jpg

which in turn discusses the second and possibly more precise method using a "Master Square" (which might look familiar):
http://i200.photobucket.com/albums/aa294/oldtiffie/Squaring-up/Trying_a_try_square2.jpg

Now, I hope that I have dealt with that comprehensively enough - once and for all.

Next, as the Original Poster (OP) referred to squares and possibly at least some of the methods of making/milling them, I thought I'd cover that as well so that the OP had his questions answered:

http://i200.photobucket.com/albums/aa294/oldtiffie/Squaring-up/Be_square1.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Squaring-up/Be_square2.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Squaring-up/Be_square3.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Squaring-up/Be_square4.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Squaring-up/Be_square5.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/Squaring-up/Be_square6.jpg

lazlo
06-16-2008, 08:45 AM
It seemed to me that all of you just jumped in assuming the wrist-pins were accurately round, straight and parallel.

No.

Jay (TipTop) posted that he found some wrist pins, and asked how he can measure if they were round and straight. Paul, Forrest and I showed him how to do that.

Case closed.


Now, I hope that I have dealt with that comprehensively enough - once and for all.

Not really Mick. We answered Jay's question, and you're going off on tangents about try-squares and toolmaker's buttons... :p

TGTool
06-16-2008, 11:19 AM
I dunno. I think Tiffie got there in the end. The very last page of his link references show exactly what Forrest was hinting at in the beginning. You use an indicator and front edge of the base to zero the indictor, then rotate the wrist pin to see any out of square error (double error).

Rather like the Texas rancher trying to impress a visitor with the size of his spread. "If I drive out the gate and along the fenceline all around my ranch, it takes me two days to get back." "Yeah," the visitor said, "I know what you mean. I had an old pickup like that once myself."

lazlo
06-16-2008, 11:46 AM
I dunno. I think Tiffie got there in the end. The very last page of his link references show exactly what Forrest was hinting at in the beginning.

You're right Jan -- I didn't bother clicking through all his linksi, but Tiffie posted the entire "Be Square" chapter from James Harvey's "Machine Shop Trade Secrets." I don't know if he realizes that on the last page Jim Harvey describes the exact procedure that I outlined on page 2 of this thread. :D

The method I described (from Karl Moltrecht's Machine Shop Practice) adds a third measurement 90 from the first two, so you can calculate lean. The first two measurements, 180 apart, as described by myself, Paul, Forrest and Harvey's book, only give you taper:


To check a cylindrical square:


Mount it on your mill table, and put a DTI in a Zero-Set holder in the spindle.

Find the tangent at the bottom of the cylinder on one edge of the square by feeding the saddle in and out and finding the high spot.

Preload the DTI, and wind the spindle/DTI from the bottom to the top. Measure the difference.

Without touching the cylindrical square, spin the indicator holder to the opposite site (180 from where you were), find the high spot again and wind the spindle/DTI from the bottom to the top. Measure the difference.

Now rotate the DTI holder 180 (back to where it was), rotate the cylinder 1/2 a turn and repeat the process.


From those three measurements, you can calculate the taper and lean of the cylindrical square with simple trig.


So using a ordinary surface gage, like Forrest described, or a special-purpose surface gage like Jim Harvey shows, is basically a dedicated fixture to do the 2- or 3 point taper and lean measurements. Like I posted earlier in the thread, you can do the same measurement in the mill or lathe, because the measurements average out the runount of the spindle bearings, and the slide-ways aren't moving.


Rather like the Texas rancher trying to impress a visitor with the size of his spread.

LOL! Quite apropos :D

tiptop
06-16-2008, 02:35 PM
So, I believe I am starting to understand how, I may (more accurately) check these used wrist pins for taper, concave, or convex and being square. If a person were to take a surface gauge as shown in oldtif's last link, but it had a "V" on the face that contacted the "cylindrical square" and then proceeded to do the tests that have been mentioned by several of you in different ways, he would then have accurate numbers to show the "case" as it may be. I think I have the tools and knowledge to perform these tests. Now I guess I should do it before class, as I am sure the teacher will want to grade my work. Boy did I get myself in a pickle this time, maybe I ought to keep my mouth shut when running into what I thought was just a good score. Oh well. Thank you everyone, for all the input, I really am enjoying the banter and learning at the same time. Of course if it looks as though my take on the information is not quite proper or true I expect I will here about it. Jay

TGTool
06-16-2008, 03:27 PM
LOL! Quite apropos :D

Usual precautions apply. That is, "Never ask a cowgirl the size of her spread."

lazlo
06-16-2008, 03:35 PM
If a person were to take a surface gauge as shown in oldtif's last link, but it had a "V" on the face that contacted the "cylindrical square" and then proceeded to do the tests that have been mentioned by several of you in different ways, he would then have accurate numbers to show the "case" as it may be.

You don't need the special-purpose surface gage from Jim Harvey's book (that's in Tiff's last link). The general idea is that you run a DTI from the bottom to the top of the cylinder on opposite sides (and between the two, if you want to measure lean).

So you can either set the cylinder up under a mill spindle, and spin the DTI around with a Zero-Set type indicator holder (like you do when you tram the head), or you can set it up on a lathe faceplate like Paul described, or you can use the crotch of a traditional surface gage, as Forrest described.

By the way, Forrest's method is one of the old machinist's trivia questions: what's the mirror for in a Gerstener chest, and what's the ball for on the end of a surface gage scriber, ... :)

oldtiffie
06-17-2008, 07:37 AM
You don't need the special-purpose surface gage from Jim Harvey's book (that's in Tiff's last link). The general idea is that you run a DTI from the bottom to the top of the cylinder on opposite sides (and between the two, if you want to measure lean).

So you can either set the cylinder up under a mill spindle, and spin the DTI around with a Zero-Set type indicator holder (like you do when you tram the head), or you can set it up on a lathe faceplate like Paul described, or you can use the crotch of a traditional surface gage, as Forrest described.

By the way, Forrest's method is one of the old machinist's trivia questions: what's the mirror for in a Gerstener chest, and what's the ball for on the end of a surface gage scriber, ... :)

First of all lazlo, you are wrong.

Your method that you espoused at page 2 post #13
http://bbs.homeshopmachinist.net/showpost.php?p=362709&postcount=13

You used a machine slide - whether it be a quill feeding down or a knee feeding up where-as Harvey used a known static square with the the indicator static on the mast and at the same height from the reference base. This method certainly found the "out of square" which manifested itself as a "tilt" indicated by changes in the indicator. It did not and could not have detected any "out of round" or out of straightness in any item similar to the OP's wrist pin/s.

Forrest's method was similar in many respects, but neither he, Harvey nor I moved the indicator up/down - it stayed at the same height through-out.

Using the "Master Square" would have faired no better in that regard.

Your method at post #13 was/is:

To check a cylindrical square:


Mount it on your mill table, and put a DTI in a Zero-Set holder in the spindle.

Find the tangent at the bottom of the cylinder on one edge of the square by feeding the saddle in and out and finding the high spot.

Preload the DTI, and wind the spindle/DTI from the bottom to the top. Measure the difference.

Without touching the cylindrical square, spin the indicator holder to the opposite site (180 from where you were), find the high spot again and wind the spindle/DTI from the bottom to the top. Measure the difference.

Now rotate the DTI holder 180 (back to where it was), rotate the cylinder 1/2 a turn and repeat the process.


From those three measurements, you can calculate the taper and lean of the cylindrical square with simple trig.

I scratch those numbers on the top of the cylindrical square, so I always know what I'm working with...

First of all you did not say the mill was correctly trammed and if there was a tram error what its direction and magnitude was. Any such tram error if not accounted for would indicate this error as a "false positive/negative" on an otherwise perfect/acceptable "square" (wrist pin?).

Second, you only sought the error in one axis (either "X" or "Y"). It is quite possible that you got no indicated error where you indicated but that the error was in the other ("X" or "Y" axis as the case may be) - or anywhere in between and you would have missed it. Further, I'd have carried out that procedure at 45 degree intervals - or finer.

Third, you used a machine slide/quill to run the indicator up and down. If the slide or quill was not a very good fit in very good condition there may have been "lateral float" that might also not be detected but will show up as (another) "false positive/negative".

Fourth, you method is not the same as Harvey's or Forrest's either at Post #14 as he did not move the indicator up/down either - only you did that out of all of us.
http://bbs.homeshopmachinist.net/showpost.php?p=362740&postcount=14.

Fifth, the "master square" in the other reference, is as said a perfect square if it is accurately round, straight and with machined ends (lathe or "side-wheeling" on a cylindrical grinder).

Sixth, my methods do not resemble Harvey's at all.

Seventh, I said that I would not use machine slides.

Eighth, the Tool-makers Buttons while perhaps OT as far as the Original Post(er) (OP) is concerned were right on the mark in response to Paul Alciatore at Post #11
http://bbs.homeshopmachinist.net/showpost.php?p=362705&postcount=11


The only method I know for self-checking a square is to place it against a straight edge and scribe a line with it. Then reverse it and scribe another line starting at the same point. If the lines diverge, the square is off.

But this method is not going to give you tenths, perhaps only accurate to a few thousanths. And it is limited by the straightness of the straight edge and the width of the area available for scribing the lines.

I am sure they can be compared with blocks or cylinders, but that is not self checking.

Paul's proposition was very close indeed to test the try-square (as suggested by Forrest) as the solution "using 2 lines" was very close to the "Tool-makers Buttons" link at:
http://i200.photobucket.com/albums/aa294/oldtiffie/Squaring-up/Trying_a_try_square1.jpg

Ninth, my posts links to Harvey's methods of making a square in a mill are very relevant to the subject of machine/d squares and as an alternative way of making a quite useful and serviceable "machine square".

Paul A at Post# 12 at:
http://bbs.homeshopmachinist.net/showpost.php?p=362706&postcount=12

suggested using a lathe face-plate. I would agree with that if the face-plate was known to be very flat and neither concave not convex as the "out of flat" will or may introduce an error or (((180) - (cone included angle))/2) which will be a contributing error ("false positive/negative").

I have explained this previously but the sketch on this link should make it obvious.
http://i200.photobucket.com/albums/aa294/oldtiffie/Squaring-up/Lathe_spindle_squareness1.jpg

lazlo
06-17-2008, 10:14 AM
First of all lazlo, you are wrong.

Machine Shop Trade Secrets:

"set the indicator to "zero" with the indicator base up against the block you're inspecting. Then check the opposite side of the block and compare the readings".

Lazlo:
Preload the DTI, and wind the spindle/DTI from the bottom to the top. Measure the difference.
Without touching the cylindrical square, spin the indicator holder to the opposite site (180 from where you were), find the high spot again and wind the spindle/DTI from the bottom to the top. Measure the difference.

I guess Machine Shop Trade Secrets, and Karl Moltrecht are wrong too :confused:


Forrest's method was similar in many respects, but neither he, Harvey nor I moved the indicator up/down - it stayed at the same height through-out.

Fourth, you method is not the same as Harvey's or Forrest's either at Post #14 as he did not move the indicator up/down either - only you did that out of all of us.

No:


Place the faceplate on the lathe. Place the square against the faceplate. Run the DI along the edge of the square using the longitudal feed on the lathe.

Jim Harvey and Forrest's method, as described, only checks the base! In order to measure the taper and lean of a cylindrical square, you have to run the DTI from the base up the cylinder.

Machine Shop Trade Secrets:

"set the indicator to "zero" with the indicator base up against the block you're inspecting. Then check the opposite side of the block and compare the readings. If the arrow does not return to zero, then your block is out of square by half the amount of that reading at that height up the block".


Third, you used a machine slide/quill to run the indicator up and down. If the slide or quill was not a very good fit in very good condition there may have been "lateral float" that might also not be detected but will show up as (another) "false positive/negative".

The quill error doesn't matter because you're taking measurements on opposite sides and adding them (same reason Rollie Dad's Method doesn't need a straight bar to measure spindle alignment). So if the quill sticks out a thou along the X-axis, the first measurement will be: (Cylinder Taper + 0.001), when you measure the cylinder on the opposite side the second measurement will be (Cylinder Taper - 0.001). Add the two measurements and divide by 2, and the quill error is gone.


Sixth, my methods do not resemble Harvey's at all.

Then why did you post Harvey's method?

Seriously Mick, you do this all the time -- someone asks a question, a bunch of people answer it, and then you jump in 20 posts later with a very long-winded post that wanders all over the place, and is rife with unrelated links. I know you're trying to help, but you end up hijacking the thread...

So now TipTop (Jay) is probably more confused than if he had never posted the question. Great. :mad:

oldtiffie
06-17-2008, 09:35 PM
Lazlo.

I will respond - again - to your post #29 at:
http://bbs.homeshopmachinist.net/showpost.php?p=363256&postcount=29

This is getting tedious. I don't see how I can reduce it to two-syllable words nor do I want to draw too many word pictures or any (more) graphical ones.


Machine Shop Trade Secrets:

"set the indicator to "zero" with the indicator base up against the block you're inspecting. Then check the opposite side of the block and compare the readings".

Lazlo:
Preload the DTI, and wind the spindle/DTI from the bottom to the top. Measure the difference.
Without touching the cylindrical square, spin the indicator holder to the opposite site (180 from where you were), find the high spot again and wind the spindle/DTI from the bottom to the top. Measure the difference.

I guess Machine Shop Trade Secrets, and Karl Moltrecht are wrong too :confused:

First of all, I don't have or have access to Karl Moltrecht's books (as I suspect that neither do most others). I made a point of scanning and posting any reference that I used - Harvey et al.

Moltrecht (and you) were the only ones who moved the indicator vertically in a machine "slide". I did not, nor did Forrest nor Harvey. Forrest and Harvey both referenced the bottom of the known square and adjusted a dial indicator at the top - and left it there.

As you quote and by inference agree with both Forrest and Harvey and that you differ from them in that you moved your indicator vertically over the test piece - and they did not - then it seems that you are wrong - not they/them.



Jim Harvey and Forrest's method, as described, only checks the base! In order to measure the taper and lean of a cylindrical square, you have to run the DTI from the base up the cylinder.

Nope - wrong again. In both the case/s of Forrest and Harvey they both used known/proven squares, set their bases (in Forrest's case, the ball of the mast of his surface guage) to the base of the reference square and zeroed the dial indicator. This is what Forrest said and meant when he said that a guage had been set. The "guage"-line is in fact between the "touch point" of both Forrest's "ball" and Harveys round base and the "zero" on the dial indicator. Both - in all subsequent positions after setting the reference guage line - used the base as a reference in any other position and measured any variation from the vertical/reference/guage line as a deviation on the dial indicator - without moving the dial indicator at all in the vertical plane as you recommended and quoted Moltrecht as a reference source.

Forrest and Harvey did - and only did - as per your quote:


Machine Shop Trade Secrets:

"set the indicator to "zero" with the indicator base up against the block you're inspecting. Then check the opposite side of the block and compare the readings. If the arrow does not return to zero, then your block is out of square by half the amount of that reading at that height up the block".

Further, the cylindrical "Master Square", if as I said previously, is sufficiently accurately round, straight and parallel and the ends "squared/faced-off" on a lathe or grinder, it is a very accurate and "natural" square that can be made with adequate accuracy by most HSM-ers without any additional tooling (reference square blocks - 1-2-3 and 4-5-6 blocks etc.) or expense and can be repaired or replicated very easily.


The quill error doesn't matter because you're taking measurements on opposite sides and adding them (same reason Rollie Dad's Method doesn't need a straight bar to measure spindle alignment). So if the quill sticks out a thou along the X-axis, the first measurement will be: (Cylinder Taper + 0.001), when you measure the cylinder on the opposite side the second measurement will be (Cylinder Taper - 0.001). Add the two measurements and divide by 2, and the quill error is gone.

That is wrong as well to the extent that any errors in "tram" or in the mechanical alignments and "fit/s" of and in the machine mechanisms - if not identified - will manifest themselves as "false positives/negatives" and show either as errors which do not exist in the item under test or are additive (+ve or -ve) and superimposed on the real state of the test piece. If I could not identify whether any such error existed I would assume that they did unless or until I could prove otherwise.

Given the status that Moltrecht has, I would assume that he would have been using a machine of the proven quality of a Jig-Borer or a Metrology class/level machine that was verified/certified and still "In test" and used under appropriately controlled conditions. Anything less would have to be "suspect" at least.

Forrest's and Harvey's methods quite elegantly virtually eliminates that variable and should "stand up" in just about any environment.

Now I will deal with your comment on Paul's method in the lathe.

Originally Posted by Paul Alciatore
Place the faceplate on the lathe. Place the square against the faceplate. Run the DI along the edge of the square using the longitudinal feed on the lathe.
I dealt with that in terms of "flatness" (and implicit and inferred "square to the spindle"). "V"-ways are by their nature, self-aligning with minimum or no practical errors if straight and not worn laterally with respect to the lathe spindle. They they are so accurate and reliable is indicated - and proven - by their known accuracy in lathes and grinders - and do not need or use gibs or any other adjustments. The ball-races in my surface grinder are a variation and a case in point in that there are two "V"-ways with balls between them - a "straight ball-race". So, I'd accept the V-way set-up in preference to any or most others.

I suspect that your use of the example of Paul's was a "red herring" as it had nothing to do with Forrest or Harvey's methods. But having said that, I'd support the reliability of the accuracy of Paul's movement a V-way above just about any other on balance - for the reasons given.


Seriously Mick, you do this all the time -- someone asks a question, a bunch of people answer it, and then you jump in 20 posts later with a very long-winded post that wanders all over the place, and is rife with unrelated links. I know you're trying to help, but you end up hijacking the thread...

Perhaps so - I plead guilty to that. But I must say that you are not innocent in that regard either - a case of "the pot calling the kettle black" perhaps?


..............I know you're trying to help, but you end up hijacking the thread..
Now, I would not (want to) be so unkind as to think or suggest this was a sort of covert "strong-arm" or intimidation attempt. But in the off chance that it is - it is very overt - so forget it - you've got no chance.


So now TipTop (Jay) is probably more confused than if he had never posted the question. Great. :mad:

Perhaps so, but TipTop is quite able to speak for himself without anyone else assuming his role and doing it for him - as it the case for anyone and everyone on the this forum.

We are all equal here.

lazlo
06-17-2008, 10:18 PM
This is getting tedious.

Yes, it is Tiffie.


Nope - wrong again. In both the case/s of Forrest and Harvey they both used known/proven squares, set their bases (in Forrest's case, the ball of the mast of his surface guage) to the base of the reference square and zeroed the dial indicator.

No, that's completely wrong Tiffie.

Jay has a wrist pin that he's trying to check for taper and lean. You can not prove the wrist pin by just checking the base. All that will do is show you the error at the base. Checking the base will not give you enough information to calculate the taper and lean of the cylinder.

You must run a DTI along the length of the cylinder to determine the tilt and lean.


That is wrong as well to the extent that any errors in "tram" or in the mechanical alignments and "fit/s" of and in the machine mechanisms - if not identified - will manifest themselves as "false positives/negatives" and show either as errors which do not exist in the item under test or are additive (+ve or -ve) and superimposed on the real state of the test piece.

You still don't get it. Do you understand why you don't need a straight test bar to tram a mill head, or to do Rollie's Dad's Method? Any tram error is zero'ed out when you do the second measurement on the opposite side and add the two measurements together. That's the beauty of the approach!


I suspect that your use of the example of Paul's was a "red herring" as it had nothing to do with Forrest or Harvey's methods. But having said that, I'd support the reliability of the accuracy of Paul's movement a V-way above just about any other on balance - for the reasons given.

Sigh. You still don't get it. Paul's method is the same as the method I described -- instead of putting the cylinder you're trying to prove under the mill spindle and running the DTI along it on opposite sides, you can put the cylinder on a lathe faceplate and run the DTI along it on opposite side. It's the same test, just horizontal instead of vertical!


Perhaps so - I plead guilty to that. But I must say that you are not innocent in that regard either - a case of "the pot calling the kettle black" perhaps?

Paul, Forrest and I answered Jay's question on page 2. As usual, you didn't read the preceding posts, and instead jumped into the thread with a long tirade that did not show the OP how to test his wrist pins, and wandered about all over the place with unrelated links.


Perhaps so, but TipTop is quite able to speak for himself without anyone else assuming his role and doing it for him - as it the case for anyone and everyone on the this forum.

You notice, of course, that Jay thanked the original responders (myself, Forrest, and Paul), but was so turned off on the thread once you started posting that he hasn't responded since. Likewise, Forrest and Paul had better sense that to try to explain their responses to you...

So let me try this one last way: Jay gives you one of his wrist pins to test. Show me how you're going to calculate a precise measurement of the taper and lean of his cylinder.

Hint: you're going to need two measurements at the top and bottom of the opposite sides, so measuring the cylinder at the base isn't going to give you the answer.
Second hint: the closed-form solution for the cylinder's taper and lean is (from my answer on page 2 :rolleyes:):



Taper = (D1 + D2) / 2

Lean = [(D2 - Taper) - (D3 - Taper)] / 2

lazlo
06-17-2008, 10:35 PM
Jay:

Since now you're probably completely confused, here's an article by Lucas Precision, a Monarch, Lodge and Shipley, Natco/Carlson, and Oloffsson (high-end machine tools and CNC) distributor as well as metrology gear:

Lucas Precision: Construction And Use Of A Cylindrical Square (http://www.lucasprecision.com/lucasprec/photo/MISC/Construction%20And%20Use%20Of%20A%20Cylindrical%20 Square.htm)

To properly check and use a Cylinder Square:

With the square on the top of the machine table, put the spindle back gears in neutral and position the head and table so that an indicator held in the spindle contacts the side of the square near the bottom end of travel.

Establish a 'zero' reading at the exact center of the square by moving the saddle back and forth to get the 'highest' reading, then set indicator 'zero'.

Traverse the head up the column and note the error and weather it is 'plus' or 'minus'. Save this indicator reading and call it reading "A". Make a light pencil mark on the base of the square corresponding to the path that the indicator traveled.

Without moving the cylinder square, re-position the indicator to read the exact opposite side of the square. Establish a 'zero' reading at the exact center of the square by moving the saddle back and forth to get the 'highest' reading, then setting indicator 'zero'.

Traverse the head up the column and note the error and weather it is 'plus' or 'minus'. Save this reading and call it reading 'B'.

Re-position the indicator to read the original side of the square. Rotate the square on the tabletop exactly 1/2 turn.

Establish a 'zero' reading at the exact center of the square by moving the saddle back and forth to get the 'highest' reading, then setting indicator 'zero'.

Traverse the head up the column and note the error and weather it is 'plus' or 'minus'. Save this reading and call it reading 'C'.

Insert the 3 readings taken above into the following formula and solve for 'T'. Please note the order of the calculation as indicated by the brackets, and perform the addition in an algebraic manner (taking into account he 'sign' of the readings). This is the amount of taper built into the cylindrical square due to manufacturing error.

T = (A + B) / 2

Insert the original readings taken above and the calculated value of 'T' into the following formula and solve for 'L'.

L = [(B-T) - (C-T)] / 2

Please note the order of the calculations as indicated by the brackets, and perform the addition in an algebraic manner (taking into account the 'sign' of the readings). This is the amount of 'Lean' built into the cylindrical square due to manufacturing error.

Insert the calculated value of 'T' and 'L' into the following formula and solve for 'L'.

D = (T + L)

Please note the order of the calculations as indicated by the brackets, and perform the addition in an algebraic manner (taking into account the 'sign' of the readings).

tiptop
06-17-2008, 10:53 PM
lazlo,
Don't worry I am not getting anymore confused than I had made myself in trying to figure a way to Check these pins. Thats one of the nice things about being very ADHD, you can think about 10 problems and / or solutions at once. I see the difference between the two testing methods and I understand about your triangulation and trig of the differences in measurements. I would not trust my 1927 9" SB to have ways that would pass muster for this ordeal. I don't know if my Fray miller would either. So I believe that puts me in the bench test park with the other camp.
oldtiffie,
I have a surfac gage that was built by a machinist that obviously new what he was up to by the quality of his craftsmanship. At this time, I do not have an attachment for my Starret last word indicator or my regular style indicator. I know I need to make some. So I tried a V block type stand with my dial indicator to see what would happen. I clamped the V block with post and indicator to my surface plate. Then I set the cylinder in the V way and set the indicator (preloaded) at the top with the dial at "0". I then spun the cylinder around slowly and found that my indicator was showing .005 runout. Now this is showing a relationship between the base and the side of the cylinder at 5.25" off the surface plate and also the possibility of an egg shaped cylinder. So then I did the same thing with the cylinder sitting on its other end and had only .002 runout.
Anyone,
So correct me if my thinking is off here so far. I have read the bedside reader (in bed) about making cylindrical squares. When making one in just one set up, you releive yourself of errors. I thought I would cut a fat one and start with an existing product, but now I need to find where the error or errows are. Now I suppose I could set it up in my mill and do a a sweep around the top of my cylinder to center it and this would also tell me if it was in fact not cylindrical but egg shaped and that would at least answer one question. I do not believe they are egg shaped at the ends though just because of the interference fit in the pistons. I think my ends are off and possibly the middle could be (which I have not checked) where the rod runs. It may be harder to true a used wrist pin than making a new cylindrical square. But the saving grace is that I don't have to have this accomplished right away. I do own a Grenby cylindrical grinder, but it is awaiting my shop addittion. Hopefully that will take place yet this summer. Any more ideas are more than welcome, I might be flunking my self imposed test. Jay

lazlo
06-17-2008, 11:18 PM
lNow this is showing a relationship between the base and the side of the cylinder at 5.25" off the surface plate and also the possibility of an egg shaped cylinder. So then I did the same thing with the cylinder sitting on its other end and had only .002 runout.

You're getting close to measuring the taper, but you don't want to move the cylinder between measurements at the base and the top, because the lean will distort the taper calculation. That's the big advantage of using a machine slide or quill.

In other words, picture the Leaning Tower of Pisa: you can have a cylinder that's perfectly round on any horizontal slice (i.e., if you measure just at the base), but it tilts in some direction. Taper, of course, would be if the tower is perfectly straight, but smaller at the top than at the base. All cylinders will have a combination of the two errors.


When making one in just one set up, you releive yourself of errors.

You minimize the errors, but won't eliminate them. Even a cylinder turned in a 10EE won't be perfectly round/straight.

By the way, that Lucas Precision link (above) also has a section on how to make a cylinder square. It's basically the same description as Guy Lautard's...


I could set it up in my mill and do a a sweep around the top of my cylinder to center it and this would also tell me if it was in fact not cylindrical but egg shaped and that would at least answer one question.

Notice I was describing how to measure the cylinder's taper and lean. Measuring roundness is much, much harder :) There's a whole chapter on measuring roundness in Moore's Foundations of Mechanical Accuracy. They start out the chapter by explaining that there's not even a metric or standard for roundness. Moore uses a polar plot showing deviation from perfect roundness, but there's no single "roundess" number.

A rough way to check roundness is to rotate the cylinder in a V-Block. But Centerless Grinders usually leave odd numbers of "lobes" on the final product and if you have 5 or 7 lobes, the V-Block won't detect the error.

This is why a plug gage won't fit into a ring gage of the corresponding size: plug gages are usually centerless ground, so they have 3 or 5 lobes, and ring gages are lapped, so they're very, very round. It's also why tool and diemakers will check a bore with both a 2-point and a 3-point bore gage -- they detect different numbers of lobes/out of roundnesses (is that a word? :D).

Moore shows their roundness checker, and there's a commercial product -- the Taylor Hobson "TalyRond", which is essentially the same thing:

http://www.taylor-hobson.com/talyrond290.htm

http://www.taylor-hobson.com/images/tr290cutout.jpg

It's basically an exquisitely-precise rotary table, with a DTI on a mast that electronically raises up from the bottom to the top of the device under test. It outputs a three-dimensional roundness chart.

For a home shop, you can do a similar measurement manually by adding more measurements to the method that Paul and I described: measure the error at several points spaced around the cylinder, from bottom to top. Map it all out and you'll have a three dimensional "roundness" chart.

oldtiffie
06-17-2008, 11:40 PM
Thanks tiptop for the call-back to the OP and the wrist-pins (we call them gudgeon pins in OZ).

First of all, go back to my post #17
http://bbs.homeshopmachinist.net/showpost.php?p=362781&postcount=17
and you will see that you don't need any more than you've got to make or check a "master/cylindrical" square. Your don't need a surface guage either - as you've shown - just something that does the job of one. Your "indicator on a shaft in a Vee-block" is just fine.

Now for the wrist pins. Test them for for straight, round and parallel with the wrist pin in vee-block and and indicator on the top of the pin. Keep the Vee-block and indicator stationary and move the pin on the vee-block and under the indicator. If you rotate the pin the indicator will show any "out of round". Move the pin along the vee-block and check for straightness and parallel in several positions (rotate the pin before moving it axially/along the vee-block.

You might also run the pin under a good micrometer (a 0.001" is fine as you can easily judge "tenths" (by eye)). You should run the pin through or over your hand as it is very good at picking up "stuff" that an instrument or the eye might miss.

If all is OK, clamp the pin in the vee-block, put the indicator on the (now) top (end) of the pin and move the vee-block (with the pin in it) under the stationary indicator. This will show the "out of square" (if any) on a good pin.

While a good surface plate is ideal, any flat surface will do.

If there is any "out of square" just mark where it is, remove the pin from the vee-block and use the side of the wheel on your pedestal grinder to remove a little of the "high" parts - re-check in the vee-block with the indicator - repeat until getting "very close" (say 0.001" to 0.002"). Then put a strip of "wet and dry" paper (used by Crash-repairers to finish paint-work) - in first "coarse" and then down to "fine/r" grades - with gas or turps. Put the pin in the vee-block and just "nip" it sufficiently to "grip" it in the vee-block. Keeping the vee-block off the W&D commence to "lap" the remaining "high spots" off while regularly re-checking with the indicator.

It should be OK if within "two tenths" (0.0002") - but better is better of course.

Making a new "master square" is relatively easy as I showed in a previous thread. I used precision cold-drawn steel tubing which was fine. Anything similar will do. I checked my material before I started by mounting it in my (as new "Chinese" - very good) lathe by indicating less than 2 tenths at each end and then running my lathe (on vee-ways) along its length in at least 4 positions.

So, I'd guess that you've got all that is needed really.

I used my "squares" to "true-up my angle plates as well - great result.

I've seen and been very impressed with your machines and what you have done on them and likewise with your postings and have every reason to think that you can and will "do it".

I have some other "issues" to deal with on this thread - as I guess you've noticed - but they should not affect or impact on what I've said here.

If there is any way I can help please ask or say - here, or PM or email - your choice.

Go for it.

lane
06-17-2008, 11:46 PM
Boy this bunch goes on and on and on. All methods will work . Aint none of you building rocket ships and going to the moon. Are making Rolex watches. so settle down boys.

lazlo
06-17-2008, 11:53 PM
Lane, my issue was that Tiffie, as usual, jumped in and hijacked the thread, without reading the solutions presented by myself, Paul and Forrest.


All the previous posts seem to assume/presume that the wrist pins are new, in pristine condition, are round and straight and neither tapered nor worn.

??? :confused:

oldtiffie
06-18-2008, 03:42 AM
Boy this bunch goes on and on and on. All methods will work . Aint none of you building rocket ships and going to the moon. Are making Rolex watches. so settle down boys.

That's probably so Lane.

Taking your advice at face value (lots!!), then if all methods are equally valid then it is entirely - and only - up to each person to make his own judgment as to which method he will use consistent with his resources and requirements for an acceptable outcome.

John Garner
06-18-2008, 05:12 PM
The Lucas Method of checking a cylindrical square analytically combines the (Top - Bottom) differences of three pairs of dial gage measurements, each of which represents the physical summation of three error terms:

A) the difference in cylinder radius at Top and Bottom

B) "lean" of the cylinder

C) "lean" of the machine column.

Taken one at a time, the three Top - Bottom differences are essentially these:

Difference 1 = A + B + C

Difference 2 = A - B - C

Difference 3 = A - B + C

Three equations, three unknowns. Elementary algebra is sufficient to derive the three individual error terms.

Or so the theory goes.

In reality, each of the Differences is contaminated by some differing amount of non-repeatability in the position of the dial-gage-carrying machine head on the column. Lucas apparently believes that the head-on-column non-repeatability has already been reduced to some negligible amount by the time they are ready to check column lean, but I'd sure like to see its negligibility demonstrated by measuring a half-dozen or so Top - Bottom dial gage differences with the cylinder-square-on-table and dial-gage-on-column held constant.

Forrest Addy
06-18-2008, 06:46 PM
You guys are sure making a simple but careful metrological procedure complicated.

I say this again: squares having parallel reference surfaces (ie: the opposite sides of the beam for a hard square or the opposite sides of a cylinder square) are self checking by the reverse error procedure. Don't need no algebra, machine spndles, or heated arguement.

All you need is a flat reference, a surface gage (or simulacum), and a dial test indicator.

My earlier post went through ALMOST all the steps. The one I omitted dealt with proving the parallelism and linearity of the opposite sides of the square. I thought that was a no-brainer.

You can use this procedure at any scale of prcision you choose. Thousandths in the casual home shop or parts of millionths for reference standard calibrations in the metrology lab. And it gives you an actual number and the sign of the error. And it's quick. And it uses nothing more than stuff from the tool box.

The first time you see the procedure in action you will Homer (holler "D'oh!" and slap your foreheads). I will make it a point to discuss this at the scraping class this weekend.

lazlo
06-18-2008, 07:57 PM
The Lucas Method of checking a cylindrical square analytically combines the (Top - Bottom) differences of three pairs of dial gage measurements, each of which represents the physical summation of three error terms:

Difference 1 = A + B + C
Difference 2 = A - B - C
Difference 3 = A - B + C

Three equations, three unknowns. Elementary algebra is sufficient to derive the three individual error terms.

Yep, you got it John! Get the man beer! :D


Or so the theory goes.

Like I mentioned earlier, the method I described is ancient -- it's described in Moltrecht's Machine Shop Practice, there's Lucas Precision, and it's also the basis of Rollie's Dad's Method.

As long as the error on the mill/lathe you're using is repeatable, it will subtract out because the measurements are 180 from each other. So the mill or spindle can be out of alignment, and the chuck and spindle bearings can have runout, but you can't have any rocking.

"Rollie's Dad's Method of Lathe Alignment

http://www.John-Wasser.com/NEMES/RDMLatheAlignment.html

What you need

• A round bar
• The bar does not have to be completely straight.

• A dial indicator
• Runout in the chuck is not a problem (for the same reason that a slight bend in the bar is not a problem).

What you DON'T need:

A tailstock, perfectly straight bar, a collet or precision chuck or any tool bits.

Why This Method Works

The bar acts as a circular cam. With a perfectly straight bar in a perfect chuck the bar is concentric with the spindle axis. Since we don't live in a perfect world there is almost always a slight offset between the center of the bar and the spindle axis. This offset varies from place to place along the bar due to slight bends and/or imperfect mounting.

At any place you pick along the bar the center of the "cam" is some unknown distance from the spindle axis. We'll call this unknown distance 'X'. As you turn the spindle axis the high measurement will be "Bar_radius + X" and the low measurement will be "Bar_radius - X".

Their average will be:

• ((Bar_radius + X) + (Bar_radius - X)) / 2 =
• ((Bar_radius + Bar_radius) + (X - X)) / 2 =
• (2 * Bar_radius) / 2 =
• Bar_radius

As you can see, the value and direction of the deviation have no influence on the final result. That is why it doesn't matter if the chuck is accurate or the bar has one or more slight bends.

If the bar is not the same diameter at both places we need to measure the diameters and adjust the readings. Averaging the high and low readings gives us a reading for the local bar radius. We convert that to a reading for the bar center by measuring the bar diameter and subtracting half the diameter (a.k.a. The Radius).

Frank Ford
06-18-2008, 09:26 PM
If you have multiple pins, how close could you get to proving the accuracy of square, straightness, and taper by working clean, standing them on end and shoving them together to see what kind of crack of light you get between two in different rotated positions?

lugnut
06-18-2008, 09:44 PM
Damn Frank, where was you six days ago before Lazlo and Tiffie got into this pissing match? You could have save us all from a week of "hard headedness" By the way, How do you measure who has the hardest head?
Mel:D

lazlo
06-18-2008, 10:00 PM
Damn Frank, where was you six days ago before Lazlo and Tiffie got into this pissing match? You could have save us all from a week of "hard headedness"

I was actually defending the solution I presented to the original poster, since Tiffie doesn't understand how it works.


But I get the message Lugnut. Tiffie hijacked the "What oil to use in my headstock" thread, the "Three Wire" thread, tried his best to hijack the "Oil Prices" and "Global Warming" threads (according to Tiffie all the posters are just "Pissing in the Wind"), and now this one. Next time I'll just let it go, and leave the OP dazed and confused.

I guess this is why the post-count is way down here on HSM, and we've lost contributors like Marv Klotz -- even Sir John rarely posts anymore. You can't even post an on-topic answer to someone's question without it turning into a flame-war.

To Frank:


If you have multiple pins, how close could you get to proving the accuracy of square, straightness, and taper by working clean, standing them on end and shoving them together to see what kind of crack of light you get between two in different rotated positions?

Depends on how lucky you are :) Seriously, you're suggesting that with a large enough sample size, the average errors will zero-out. It may work, but I'd be willing to bet that whatever error the wrist pins have (in taper and lean), they're probably very consistent, due to the mass production method.

Forrest Addy
06-18-2008, 10:51 PM
There's merit to Franks proposal. It strongly resembles the three surface solution to proving flatness but aligning pins and observing the light leaking past the tangencies introduces many sources of error. Surface finish for one (haow would a smudge or a stain affect the tranmittance?). Repetitive abutment for another. And angle of view. Also, interpretation of the light transmitted through the gap. Yet another, quantifying the readings - that is determining the amount of error so that a third party can objectively attest the item meets specifications.

The three plate solution solves this problem neatly in that the blue indications can be taken up on vellum and preserved. The dimensional limits of blue transferance are well known.

The three pin solution proposed for proving squareness works in theory but fails in producing repeatable objective results. Two guys can look at the light leaking through a near-perfect tangency and honestly differ in the interpretation. Tensioned feelers is far more repetitive and thus more likely to provide acceptable proof of gap parallelism but feeler tension is dependent on the immobility of the gages element in the measurement system. Drag a smuge past the tangency and one have of the pins shift ... start over.

lazlo
06-18-2008, 11:03 PM
There's merit to Franks proposal. It strongly resembles the three surface solution to proving flatness

The three plate solution solves this problem neatly in that the blue indications can be taken up on vellum and preserved.

There's a big difference Forrest -- in the three plate method, the three plates start off way out of flatness, and through sucessive series of scraping and spotting, you gradually improve the flatness of all three.

Frank's proposal is the equivalent of trying to determine the flatness of one of the original three plates by matching against the other plates, before all the scraping happens.

If you get lucky, and they're all close, then you can probably get a reasonable measurement out of it.

But if the wrist pins, or 3 plates, are way off, you won't be able to get a useful measurement.

In any event, any further participation in this thread and I'm going to be criticized, so I'm signing off. I think Jay knows how to check his wrist pins.

oldtiffie
06-19-2008, 12:04 AM
If you have multiple pins, how close could you get to proving the accuracy of square, straightness, and taper by working clean, standing them on end and shoving them together to see what kind of crack of light you get between two in different rotated positions?

Thanks Frank.

I think I can answer that question.


The tubes were set up in the lathe with each end being set to a maximum TIR between highest and lowest being 0.02mm (0.0008") with maximum indicated differences between opposing jaws on my 4-jawed chuck of 0.01mm (0.0004").

I first tested them as pairs by putting them on my mill table (to show those without a surface plate that it is not always needed for even very good HSM shop accuracy). I put one against the other and rotated one each 90 degree and checked again. There was no discernible variation in the width of the narrow line of light. I inverted the same one and repeated the process - same result. I repeated the entire process for the other of the pair - same result. I then repeated the process for remaining 6 (3 pairs) of tubes - same result again. I also carried out a check with the Class 1 square - "spot on".

So I now knew that the ends were square to the axis of the cylinders.

It is a direct quote from my post #1 at:
http://bbs.homeshopmachinist.net/showpost.php?p=355980&postcount=1

I used those "squares" with great success to "true-up" my angle-plates, details of which are in the same post/thread.

I tested my angle plates with my Class 1 (DIN 875/1) try-square (aka Engineers/Machinists Square) and all was good.

To answer your question in regarding "light" in the "gaps". It is at least as good as you will get with a precision try-square.

To further check things out on the squares and to get the "multiplier effect" I put the stock of the try-square on the "barrels" of the cylindrical squares with the blade across the ends. I did this at least four places on each end - good result. I reversed the try-square and put the stock on the ends and the blade on the "barrels" - same good result.

So, all in all, I got what I think is a very good result in "fairly ordinary" shop with similar quality tools.

Perhaps I was just "lucky" - perhaps - or perhaps I didn't know what I was looking for or at - I hope not - but it's possible I suppose.

I "went" for the widest practical diameter so that any of my "squares" were more "stubby" than "tall/thin", both for accuracy and especially to get a much and as big a surface as I could get on the mill/machine table due to "location"/"square", area on the table, ability to carry a load (eg squaring angle-plates etc.), and resistance to distortion due to clamping etc.

The tube I used was precision cold-drawn steel with an OD of 3" and nominal 1/4" wall-thickness and nominal 2 1/2" i.d. (Yes that's right - we still make, use and can buy "inch" stuff in a "metricated" country (OZ)).

There is a "self-checking" method using 4 discs/"rounds" that is new to me but very obvious!!:
http://en.wikipedia.org/wiki/Machinist_square

oldtiffie
06-19-2008, 07:05 AM
I had been looking = without any result that I could use - for the details re. accuracy of Engineers/Machinist squares iaw/to DIN 875 for Class 1 (inspection/reference) and 2 (general machine shop use).

I could not find anything on British Standards (BS series) or the US series either.

The best I could do was at Littlemachineshop.com (LMS) at:
http://littlemachineshop.com/products/product_view.php?ProductID=2742

I expect that these are to DIN 875/2 or US grade B or 2.

Never the less the results for what-ever grade they are are not bad at all.


(Extracted from LMS link/page)

Includes 2", 3", 4" and 6" squares
Made from high quality tool steel
True right angles inside and outside
Beams and blades are precision ground
Blade is hardened
Machinist squares made in the US by Products Engineering Corporation (PEC).

Length of blade is measured from inner edge of beam to end of blade.

These squares are square within 0.0006" over the length of the blade. The two sides of the blades and beams are parallel within 0.0005" over their length.

I would appreciate getting the links to/for the applicable standards.

TIA

Frank Ford
06-19-2008, 11:02 AM
Frank's proposal is the equivalent of trying to determine the flatness of one of the original three plates by matching against the other plates, before all the scraping happens.

If you get lucky, and they're all close, then you can probably get a reasonable measurement out of it.

But if the wrist pins, or 3 plates, are way off, you won't be able to get a useful measurement.

Exactly. I wasn't even thinking of making any kind of adjustment. I was just wondering how accurate a visual check would be, presuming the pins were exactly square on the ends, or really close. Can one reliably see a tenth, presuming all things are super clean?

Me, I'm still new enough at this that I impress myself when I manage to cut, bore or turn +/- .0005, and I wouldn't be surprised to find that becomes my ultimate limit as a home shop guy, both for ability and need.

oldtiffie
06-19-2008, 10:30 PM
........................................
.......................................

Me, I'm still new enough at this that I impress myself when I manage to cut, bore or turn +/- .0005, and I wouldn't be surprised to find that becomes my ultimate limit as a home shop guy, both for ability and need.


Frank. "1/2 a thou" is pretty good going in many shops - and all (and often more/better) than is required on many jobs.

An example.

"Tolerances" are one area that is often over done as regards level of accuracy that is sought - particularly if one part already exists and you have to make a part to fit to get the fit required - on that job.

Let's say you have a 2" shaft that has to be a light running (or any) "fit" with a part you have to bore out.

If the tolerance for a light running fit was, say:
2.0010"/2.0005" for the hole; and
2.0000"/1.9995" for the shaft;
the tolerance zone for the required fit when the parts are to be put together are:
highest: (largest hole - smallest shaft) = (2.0010" - 1.9995") = 0.0015" (+ve denotes "clearance" - ie not "interference"); and
smallest/least: smallest hole - largest shaft = (2.0005" - 2.0000") = 0.0005" (+ve denotes "clearance" - ie not "interference")

So the "clearance range " is (0.0015" - 0.0005") = 0.0010".

Now if say the shaft exists, and is say 1.9998" the hole can be bored to 1.9998" +0.0015/+0.0005 = 2.0013/2.0003" which gives the correct clearance fit tolerance range of 0.001" ( a full "thou") for the shaft and hole.

My point is that although the individual tolerances may be "tight", when taken together, that are surprisingly less and "better".

A similar approach is used for "interference" or "transition" fits - but watch out for the "signage" of the figures/values.

(It helps to sketch it out and it becomes more obvious and less confusing).

My point is that where "tolerance" and "fits" are concerned, if you "work the figures" a "difficult" "half a thou" may well be achieved using an "easy" "full thou".

Many parts in many shops are "made to suit the other part" and stay that way - so take advantage of "stuff".

Same applies to "errors" in say "cylinder/master squares".

If there is an error or "lean" of say 0.001" in a square, just rotate it 90 degrees and the "error" will "disappear" for use - but do check - just in case.

The engineer's/machinist squares at LittleMachineShop.com are excellent for most shop work as they are not more than 0.0006" "out" along the blade and parallel(ism) is very good too.

So, a bit of care and logic can get very good results by just using and taking advantage of what is available so that otherwise "difficult" jobs become less or or even "easy" (easier??).

Forrest's advice on the "gaps"was excellent and reasoned - as it always is.

I hope this helps.

tiptop
06-19-2008, 11:57 PM
First I would like to say that I am not a seasoned machinists or even apprenceship grade. I have only been at this for two years and I heard that after you serve your apprenticeship and then work for at least 10 shops for at least 2 years each you may be able to open your own shop. Having said that and knowing I will not live long enough to get the doors open this is where I stand. I took the time to play with one of these today. I checked it for being round as best I could with my caliper set up on different height gage blocks and found they were round. Then I set it up in my old SB in a four jaw and steady rest and faced off the end. Then I skipped .200 on the next cut to leave a ridge on the outside. Then off to the surface plate. As best as I could tell one side had a lean of .00425, the opposite side was "0" and the side 90 degrees out was "0". So I guess my machining techniques leave a lot to be desired today. Maybe after class I will try something different if you all are not to bored with this subject? Jay

oldtiffie
06-20-2008, 01:45 AM
.......................................
......................................
First I would like to say that I am not a seasoned machinists or even apprenceship grade.

.........................................
........................................
Then I set it up in my old SB in a four jaw and steady rest and faced off the end. Then I skipped .200 on the next cut to leave a ridge on the outside. Then off to the surface plate. As best as I could tell one side had a lean of .00425, the opposite side was "0" and the side 90 degrees out was "0". So I guess my machining techniques leave a lot to be desired today. Maybe after class I will try something different if you all are not to bored with this subject? Jay
Thanks Jay.


First I would like to say that I am not a seasoned machinists or even apprenceship grade.

You have nothing to explain or apologise for - at all. You are doing OK - and I'd guess as good as many who claim to be Machinists. Many do things on a "monkey see - monkey do" (ie "rote learning") basis and get "thrown" when something new or the the same thing in a different way comes up. You have shown that you can learn and have an inquiring mind as well as tenacity and the ability to "roll with the punches".

So, you owe an explanation or excuse or sub-ordination to nobody.

That was good work - very good work. I was going to post pretty well that in my next post - and you've pretty well done it for me - many thanks.

All of this presupposes and requires the cylinders to be as round and straight as you can get them. If there are errors, they can be identified and "worked around".

In either case, you will have quite serviceable "squares" that should suit most work in most shops with reasonable care.

I thought later after making mine, that instead of buying new material (mine was $100 per meter), I could have used the column from a smaller pedestal drill. If the roundness and straightness are anywhere as good as the cylindrical or centre-less ground finish looks, they should do the job very well at minimal cost - none if you get lucky!!

Now all you need do is mark that "zero" point and your are "in" - a good job well done.

I guess you will appreciate why I wanted mine as big a diameter (3") and as "stumpy"/short (9") maximum as that way any errors in the base will (only) be multiplied by three at the top of the tallest (9") one/s. Just use the "zero error" part for use on your machine - the rest probably doesn't matter. Get a size that will fit in your lather steady-rest - makes it a lot easier to set up and face the ends off!!!

Another "quick and nasty" (but surprisingly effective) way of checking the "run-out" at any point on the circumference of the cylinder.

Get two metal washers - any size - even "punched" will do, that are say 1/8" to 1/4" thick. "Roundness" or "flatness" is not an issue. Just use your pedestal grinder and put a bevel (any angle) all the way round one side (to ensure contact above any bevel on the end of the cylinder/s). Leave a say 1/16" to 1/8" "land".

Fix the washers to the mill table (bevelled side down, "land" side up) - nuts, screws and "T"-nuts will do - so that the "lands" contact the cylinder (on one end) about 60 degrees (not at all fussy) apart.

Stand the cylinder on its end between and touching both washers. Put a dial indicator on the top of the cylinder surface - hold with a magnetic base or similar. Pre-load the indicator and set to zero. Rotate the cylinder against the washers while reading the indicator. Note where "zero" (two - at mid-defection points) is and mark them. That is your "zero" marks. Just set them to your work each time and any errors anywhere else won't matter. No errors at all is ideal, but the least possible in the circumstances is good enough most times if used with care.

"Get 'er done".

tiptop
06-20-2008, 01:27 PM
Sorry folks, I guess my mind was not working last night, I got my measurements wrong. This is what I came up with this morning after thinking about what I had posted. Two opposite sides measure, "0" and ".007 respectively. Then the two opposite sides that are 90 degrees off measure, ".004 and ".004 respectively. I am not sure why I was not able to get a cut on the end that was square or closer to square than that. I am going to have to ponder this for a while. The reason for my exercise with these pins is to hopefully come up with something I know is square to use as a check or reference or clamping block for my other set up peices, such as what oldtiffie did in post # 17.

dp
06-20-2008, 01:29 PM
Sorry folks, I guess my mind was not working last night, I got my measurements wrong. This is what I came up with this morning after thinking about what I had posted. Two opposite sides measure, "0" and ".007 respectively. Then the two opposite sides that are 90 degrees off measure, ".004 and ".004 respectively. I am not sure why I was not able to get a cut on the end that was square or closer to square than that.

Sounds like the cylinder is tapered, no?

John Garner
06-20-2008, 03:00 PM
Testing perpendicularity in the manner Forrest Addy describes is a common practice in metrology, but it's important to realize that the technique is totally blind to a difference in the diameters at the of the would-be-cylinder being tested at its "hard" and "indicator" contact points.

Consider as an alternative to a conventional cylindrical square the variant commercialized by Hermann Schmidt, pictured on their website at https://www.hermannschmidt.com/productcart/pc/viewPrd.asp?idcategory=8&idproduct=229

Hermann Schmidt's picture makes the squareness-checking process self evident, but as with the conventional cylinder square, the surface-gage-and-indicator won't find taper in the "square cylinder" object.

A roll-your-own "square cylinder square" should be fairly straight-forward, and the meaningful errors are constrained to a single plane . . . unlike a conventional cylindrical square that really needs to be measured and evaluated in both the "North / South" and "East / West" perpendicular planes.

Of course, if you wanted to made a four-sided "square cylinder square" . . .

John

lazlo
06-20-2008, 04:28 PM
Testing perpendicularity in the manner Forrest Addy describes is a common practice in metrology, but it's important to realize that the technique is totally blind to a difference in the diameters at the of the would-be-cylinder being tested at its "hard" and "indicator" contact points.
...
as with the conventional cylinder square, the surface-gage-and-indicator won't find taper in the "square cylinder" object.

Thanks John -- I've made that point several times in this thread:



Nope - wrong again. In both the case/s of Forrest and Harvey they both used known/proven squares, set their bases (in Forrest's case, the ball of the mast of his surface guage) to the base of the reference square and zeroed the dial indicator.

Jay has a wrist pin that he's trying to check for taper and lean. You can not prove the wrist pin by just checking the base. All that will do is show you the error at the base. Checking the base will not give you enough information to calculate the taper and lean of the cylinder.

You must run a DTI along the length of the cylinder to determine the tilt and lean.

On the last page of Machine Shop Trade Secrets that Tiffie posted, Jim Harvey is showing how to check the perpendicularity of a square block, so taper is not an issue. As Jay is finding, it is an issue with a cylindrical square:

http://i164.photobucket.com/albums/u15/rtgeorge_album/Harvey.jpg

lazlo
06-20-2008, 04:31 PM
Hi Jay,


Two opposite sides measure, "0" and ".007 respectively. Then the two opposite sides that are 90 degrees off measure, ".004 and ".004 respectively.

If you refer back to that formula I posted on the 2nd page, that's saying your cylinder has a taper of 3 1/2 thou, and virtually no lean.
Have you leveled and adjusted the lathe with the two collars method?

Keep at it! :)

Robert


Say the first measurement was D1, and the second measurement 180 opposite was D2:

Taper = (D1 + D2) / 2

Now the third reading, with the cylinder rotated and the DTI back at the start is D3:

Lean = [(D2 - Taper) - (D3 - Taper)] / 2

John Garner
06-20-2008, 05:15 PM
If tiptop made his measurements using a surface gage and indicator, using the technique explained by Forrest Addy and shown in the illustration old tiffie excerpted from Machine Shop Trade Secrets, the test results indicate that 1) tiptop's "cylinder" leans somewhere around 3 1/2 mils in one direction only, and 2) that there is some differential out-of-round between the top and bottom gage contact areas . . . but his measurements can't rule out taper or stepping.

As a mental exercise, consider a stepped cylinder with half of its length of one diameter and the other half a second, coaxial, diameter. Imagine then that the base of the surface gage contacts one step and the dial indicator tip contacts the other step. Would the dial indicator reading change as the stepped cylinder is rotated around its axis?

No.

How about if, instead of having a stepped cylinder, we have a cone. Will the indicator reading change if the cone is rotated around its axis?

No again.

Finding the stepping or coning requires either measuring the diameter of the pseudo-cylinder at the two gage-contact points or inverting the pseudo-cylinder relative to the surface gage and dial indicator and again rotating the pseudo-cylinder around its axis.

The Lucas Method data reduction algorithm isn't appropriate if the Forrest Addy / Machine Shop Trade Secrets Method of testing is used.

John

lazlo
06-20-2008, 05:38 PM
If tiptop made his measurements using a surface gage and indicator, using the technique explained by Forrest Addy

I got the impression from Jay's previous posts that he was doing those measurements with a DTI in the mill or lathe spindle, and that those measurements were the differences in the top and bottom DTI reading on opposite sides of the cylinder.

If that's the case, Jay's measuring 3 1/2 thou of taper, and the second two measurements, taken at the starting point after you've rotated the cylinder a 1/2 turn, indicate that there's virtually no lean. That's what you'd expect on cylinder turned on a lathe.

If those measurements are at the base with a surface gage on a surface plate, then that's 3 1/2 thou of eccentricity at the point the DTI contacts the cylinder (i.e., it's off the perpendicular plane with the base by 3 1/2 thou). To calculate the lean, you still need two measurements at top and bottom of the cylinder...


The Lucas Method data reduction algorithm isn't appropriate if the Forrest Addy / Machine Shop Trade Secrets Method of testing is used.

Agreed, but I think we're talking about two different tests. The surface gage/surface plate method can only check out of roundness at one point: it's basically checking whether that point where the DTI touches the cylinder is perpendicular with the surface plate. So as we've both mentioned, it can't detect taper on the cylinder.

By the way, the trick to Moltrecht's method which separates the taper error from the lean error is that after you've made the first two measurements at two points 180 apart, you return the mill/lathe spindle (and DTI) back to the first point, and then rotate the cylinder half a turn. Then take the third measurement.

If you don't do that 1/2 turn of the cylinder (and the third measurement), you can't distinguish between the taper of the cylinder and the lean of the cylinder.

lazlo
06-20-2008, 05:43 PM
consider a stepped cylinder with half of its length of one diameter and the other half a second, coaxial, diameter. Imagine then that the base of the surface gage contacts one step and the dial indicator tip contacts the other step. Would the dial indicator reading change as the stepped cylinder is rotated around its axis?

How about if, instead of having a stepped cylinder, we have a cone. Will the indicator reading change if the cone is rotated around its axis?

John, you're re-describing why taking a measurement at the base, as with Forrest/Harvey's method, doesn't detect taper or lean.

I've explained that several times since page 2, so I'm in complete agreement :D