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customcutter
05-19-2012, 03:43 PM
OK, I've read several threads on "leveling" a lathe, and I understand it's not necessary to level, just necessary to get everything in a horizontal plane.

My question is, is RDM for aligning the headstock with the ways, and tailstock? Horizontal and vertical alignment by adjusting the headstock? Or is he talking about shimming the "feet" of the lathe in his discription to achieve alignment?

My lathe is a 14X40 so I only have 4 "feet" instead of six for larger lathes. I guess I'll start by making some "jack bolts" to insert under the "feet".

thanks,
Ken

TGTool
05-19-2012, 04:23 PM
RDM's method is just about eliminating the twist in the bed - shimming adjusting the feet. Visualize an imaginary line that's the lathe spindle centerline projecting straight out down the bed towards the tailstock. Now imagine that the bed is a little twisted as though the tail end was unscrewed. As the carriage progresses down the bed towards the tail the tool is going to be pulled a little away from the centerline and just a teensy bit down. That's the quality that the RDM method is trying to measure and allow you to correct.

.RC.
05-19-2012, 04:34 PM
I would not use "rollie's dad" method on any lathe other then a very light bench lathe like a small short South Bend..

IMO using that method on a larger lathe is useless..

customcutter
05-19-2012, 04:36 PM
Just checked my lathe using RDM. Using a 30" hydraulic cylinder ram that measured 1.001" on both ends. I got .004" of run out in the horizontal measurement, and .006" in the vertical.

Being I just got it back into position I think I'll let it set for a few days and settle in before trying for anything better.

Also only got .0005" run out on the 3 jaw chuck. :D Very happy with that, I wonder if it is the original Taiwan or aftermarket. I'll have to check.

thanks,
Ken

J Tiers
05-20-2012, 12:32 AM
RDM can measure the twist, IF you already KNOW that the headstock is aligned.

OR

RDM can measure the alignment of the headstock, IF you already know the bed is level / not twisted.

RDM is all "internal", all "self referencing". You need an external reference, like a level, to do the whole job.

In fact, RDM is just a fiddly and error-prone replacement for the "two collars" test, and to make matters worse, it is not a test of actual operation (which the collars test IS).

Don't make the mistake of thinking it is magic hidden knowledge of some sort. It's just a test of the relation of spindle axis to bed, and probably not the best one, at that.

Forrest Addy
05-20-2012, 03:25 AM
The RDM has its vociferous adherants but in fact it's a waste of time advanced by the ignorant but enthusiastic to - in all good faith, BTW - innocently deceive the ingnorant but equipment poor. The RDM seems simple and effective - and it is in a limited way - but most of its appeal lies in the hocus-pocus facor. By the time you go through all the interations you still don't know what you have. The RDM is time consuming and non-quantitive, except in the final cuts.

There is one inescapable fact about the Rollie's Dad's Method: no skilled equipment re- builder, millwright, production or job shop, or manufacturer uses it or any method like it to align their machine tools.

The next question is: if no competent craftsman uses RDM, why should you?

A level, a two collar test or proof bar, basic mechanic's tools, etc, and cutting tests yields the best results in aligning a lathe to "test sheet ready " in the least time. If you don't have this minimum equipment, round it up. You will need it for annual checks and new machine installations anyway even in the home shop. With these one man can set up and align a new lathe 20" and smaller to factory specs in a couple of hours, and a worn lathe to best compromise in 4.

Paul Alciatore
05-20-2012, 04:22 AM
I believe I was the one who suggested "searching for Rolleys Dad's Method" in another thread. Perhaps I should have been more specific. I said to look it up, but I did not say to actually use it. You will find a great amount of information in those posts, much of it better than RDM. I am sorry if I caused any confusion.

Forrest Addy
05-20-2012, 05:51 AM
Paul. I kinda gathered that when I skimmed your response. However mention of RDM in any contest seems to bring its adherants out of the woodwork and I wanted to scotch building enthusiasm. Hence, my red-eyed vigor.

If my words put you in a bad light, I'm sorry. That wasn't my intention. Call it friendly fire.

customcutter
05-20-2012, 11:19 AM
I did a search last week of this site and I think the key words were "lathe level" or "lathe leveling".

There was a lot of discussion on 3-4 threads about the lathe not actually needing to be level at all "lathes on ships, etc." However it was simply a means a putting everything into a measureable horizontal plane. I understand and agree with all of this. However, in one of the post RDM was mentioned and the method seemed simple enough, and seemed to make sense. Since then I have read other post in other threads/forums and looking for some advice on whether it was meant to shim the headstock or shim the feet of the lathe? Not trying to start a heated discussion. Never realized that as some have said that it is for "mini-lathes".

I'll look up the two-collar method and see what that involves.

thanks,
Ken

customcutter
05-20-2012, 01:33 PM
Did another search on the "two collar method" trying to digest everything for now.

I'll start by leveling the lathe and work from there.

thanks,
Ken

Alistair Hosie
05-20-2012, 04:18 PM
Sorry I never heard of Rollie or his Dad who are they or are they an American myth that is unknown here????Alistair

beckley23
05-20-2012, 05:07 PM
Be glad you never heard of Rollie's Dad's Method. IMO, it is designed to be used on used lathes by those who don't have the proper level. You place a bar in the chuck, and start taking cuts at each end of the bar. Measure the ends and make adjustments by placing shims under the offending foot of the lathe. It struck me as a pure guessing game, that would take an enormous amount of time with very questionable results. What the method does is to deliberately twist the bed so that one can turn a parallel shaft for that particular distance, then you get to do it over again for a different length. To me it's pure hocum, or as Forrest says "hocus-pocus".
It's similar to the 2 collars test, but a level is not used, and as result there are no controls. IMO, it's a scam perpetrated on the unsuspecting, looking for the magic cure.
I read the instructions several times before I figured it out.

Using 2 levels, one to rough the lathe in, and the other with with .0005" graduations to fine tune, I generally can get a lathe leveled in under an hour. When I relocated to my new shop, I taught my apprentice son how to level the lathe. I was the wrench turner and he told me which way to turn the wrench. He had never used that level before. I thought it would take 2 hours, but 45 minutes later the lathe was within a couple tenths end to end. The lathe has 4 leveling screws at each end.
Harry

tdmidget
05-20-2012, 06:13 PM
Sorry I never heard of Rollie or his Dad who are they or are they an American myth that is unknown here??"


"here"? Where is that?

Errol Groff
05-20-2012, 06:31 PM
The topic under discussion here is properly called "Rollie's Dad's Method of Lathe Alignment" and the instructions may be found here:

http://neme-s.org/Rollie's_Dad's_Method.pdf

Before this discussion drifts any further into the realm of name calling let's all recognize that Rollie's dad used this method with fine results for him and he was a talented and respected tool maker in Massachusetts.

I am somewhat surprised that laser interferrometers have not yet been mentioned.

If you don't think RDM is right for you then please don't feel obliged to use it!

I try not to get worked up by things like this but Rollie is a long time friend and talented HSM craftsman. His dad was a great fellow as well and is mised by all who knew him.

lazlo
05-20-2012, 06:47 PM
I did a search last week of this site and I think the key words were "lathe level" or "lathe leveling".

There was a lot of discussion on 3-4 threads about the lathe not actually needing to be level at all "lathes on ships, etc."

Bless your heart! Lathe leveling is one of those religious items like "billet", aircraft aluminum, and whether to mash knurls :)

You're a lot better off reading a description of the two collar method in a machinist text than to try and filter the threads here, IMHO...
Most texts tell you to level the lathe, then adjust the legs on the lathe until the collars match. HTRAL, for example:

"The leveling may be perfected by adjusting the shims under the front and back legs until the collars on the test piece are turned the same diameter."

Rollie's Dad's method skips the leveling, and goes straight to shimming.

customcutter
05-20-2012, 07:05 PM
Went to Lowe's and picked up 4 2" X 1/2" carriage bolts, 4 3/4" flat washers, and 4 nuts with nylon inserts. Spot welded the bolts on top of the washers, and tightened the nuts down as close as I could and still had clearance to get a wrench of the flats of the carriage bolts. 4 home made leveling pads for $6.72.

Using my HF level, accuracy .0005"/in. I had to raise the front on both ends approx 1/8", then raised the headstock about 5/16" front and rear to level along the ways. That's as close as I can get until I have a friend come over with his Starrett level.

Just for kicks I chuck up the hydraulic ram again and did the RDM. Had .000 runout at the chuck (previous owner must have ground it), and the end of the bar I had .004", roughly 30 inches long less what I have chucked up.

I still plan on leveling with a machinist level and doing the 2 collar method.

thanks,
Ken

J Tiers
05-20-2012, 07:36 PM
Errol:

I'm pretty sure you are correct about the various characters of the "culprits"....

BUT.....

It's up to the advocates, which I assume includes you, to prove to the rest of us how RDM is better than, and sufficiently replaces, the *combination* of a level (for twist) and the two collars test (for H/S alignment to the "effective bed", which includes wear, etc).

I submit that nobody CAN prove that, because it ain't true...... RDM cannot do *both* things.

I agree that in theory, at least, it CAN do either one, but not both at once. You have to come in with a known situation, OR you will have a mess. The obvious and best approach is to level first.

This is also true of two collars, of course, because they are equivalent in theory. And indeed that is what industry did.... level, and do two collars test to verify alinement.

I am not quite sure what "equipment" is avoided with RDM.... probably the precision ground test bar.... but with the two collars test it isn't required. All you need is a mic to measure diameters, and a suitable piece of scrap stock.

If the intent is to avoid the level, then I am afraid that regardless of "talent", someone either failed to comprehend the problem, or failed to accurately reproduce the procedure.

Over to the rest of you now............

lazlo
05-20-2012, 07:47 PM
It's up to the advocates, which I assume includes you, to prove to the rest of us how RDM is better than, and sufficiently replaces, the *combination* of a level (for twist) and the two collars test (for H/S alignment to the "effective bed", which includes wear, etc).

I haven't read the write-up in years, but I'm pretty sure Rollie's Dad's method is intended to be a way to get a lathe up and running if you don't have a precision level.

I'm not advocating RDM, just saying...

beckley23
05-20-2012, 08:29 PM
When I was doing the work-up on the Monarch Series 60 a couple years ago, as an act of desperation with the turning tests results I was getting, I resorted to RDM. The results got worse. I screwed around with it for about 3 hours, I even had the use of a level, and finally gave up. That was the first time I tried RDM, and it was the last time. It was time to do the proper corrections, to get the results I wanted.
Harry

.RC.
05-21-2012, 01:16 AM
Just for kicks I chuck up the hydraulic ram again and did the RDM. Had .000 runout at the chuck (previous owner must have ground it), and the end of the bar I had .004", roughly 30 inches long less what I have chucked up.



Hydraulic ram rods are not usually straight..

Jaakko Fagerlund
05-21-2012, 04:01 AM
Hydraulic ram rods are not usually straight..
And most likely not perfectly round either (usually they are ground S355 + hard chroming or 42CrNiMo with a hard chroming). And when you chuck something 30" long for a couple of inches of gripping range, no matter what type of chuck you have, you will most definately get a runout.

J Tiers
05-21-2012, 08:21 AM
I haven't read the write-up in years, but I'm pretty sure Rollie's Dad's method is intended to be a way to get a lathe up and running if you don't have a precision level.

I'm not advocating RDM, just saying...


And I'm "pretty sure", after actually reading it years ago, that you'd do about as well by just oiling the machine and starting to use it.....

if you try to follow RDM to actually make a basic alinement *from scratch*, and not to just "tweak" an existing "known to be reasonable" alinement, you'll likely twist the bed into a pretzel chasing the numbers... That applies DOUBLE to the usual "practitioner", who is new to all things machinery, and reads about the "magic secret knowledge" known as "Rollie's Dad's method".

Such an individual is not likely to understand when the adjustments are getting ridiculous and it is time to stop and do something different.

Plus, I challenge ANYONE to explain why and how making dozens of delicate measurements with an indicator (every newbie has lots of THOSE, and knows all about using them, right?) is simpler and easier than making TWO simple micrometer measurements per trial with the "TCT" (two collars test).

Especially when "TCT" actually tests the results you DO get, not "the potential error you might get if these delicate measurements are ALL exactly correct and everything works out just exactly right".

Rollie may be a great guy, and Rollie's dad may have been a smart cookie, but it STILL looks like the very longest way and roughest road by which to get to the result.

Jakko:
I will say that RDM does not depend on the test rod being straight.... but it DOES depend on the rod roundness being better than the error you can tolerate.

GadgetBuilder
05-21-2012, 02:07 PM
And I'm "pretty sure", after actually reading it years ago, that you'd do about as well by just oiling the machine and starting to use it.....

<snip>
Plus, I challenge ANYONE to explain why and how making dozens of delicate measurements with an indicator (every newbie has lots of THOSE, and knows all about using them, right?) is simpler and easier than making TWO simple micrometer measurements per trial with the "TCT" (two collars test).

Especially when "TCT" actually tests the results you DO get, not "the potential error you might get if these delicate measurements are ALL exactly correct and everything works out just exactly right".
<snip>

Jerry,

I didn't realize your criticisms were theoretical and based on reading RDM rather than actually trying it. I'd be interested to hear what the dozens of measurements you mention are and what they're used for.

I've actually used RDM and had good results from it. By that I mean that I reduced the taper cut by my lathes to acceptable, which was my original goal.

There seem to be a few versions of the "two collars test" = TCT. The descriptions I've found are:

http://www.wswells.com/data/howto/H-3.pdf South Bend

http://www.wrathall.com/Interests/machining/Testing%20lathe%20for%20accuracy.pdf J. Latta

http://bbs.homeshopmachinist.net/showpost.php?p=770807&postcount=3 Forrest

http://www.chaski.org/homemachinist/viewtopic.php?f=42&t=76959&p=101250&hilit=RDM#p101250 J Tiers

The J Tiers link is to a thread from several years ago where you raised a number of issues with RDM and I learned more about it. When I raised questions about use of the TCT per your description you didn't address them but instead said that lathe manufacturers used the TCT so it shouldn't be questioned., i.e the Argument from Authority fallacy.

It's interesting that in Forrest's description of the TCT he indicates that making the cuts on the collars is much more difficult than your description linked above would lead one to expect. In fact, he suggests using a piece of wood to damp chatter and polishing the resulting collar area to reduce roughness. Converting theory to practice can be messy :D

My take on RDM is that it allows one to measure the deviation between the spindle axis of rotation and the ways. These may be non-parallel because the headstock is mis-aligned and/or the bed is twisted. In Forrest's description of TCT he says this is the complicated part... but then doesn't say how to separate these causes. My thought is that RDM allows me to get information equivalent to that provided by the TCT but more quickly and easily.

I'm still learning about RDM so detailed info about WHY it doesn't work rather than broad generalities would be helpful. I'm trying to figure out, in detail, what I've misunderstood about RDM since my experience is quite different from that reflected in this thread.

J Tiers
05-21-2012, 08:40 PM
When I raised questions about use of the TCT per your description you didn't address them but instead said that lathe manufacturers used the TCT so it shouldn't be questioned., i.e the Argument from Authority fallacy.

.

100% FALSE.....

The comment was not that it "should not be questioned"...... as you suggest...

In contrast to your erroneous remark, the idea ACTUALLY was that since that is how the manufacturer tested, it makes sense to use it again... you are more likely to get the same results in the same conditions.....

RDM is aimed at the novice, the one least able to get consistent results from it, as I think most would agree... That is my objection..... and why I bother to spend the time typing... I don't have to, and I don't give a rip if you "listen" or if you think I am an ass..... Doesn't hurt me a bit, I've got thick skin.

Of course, as far as the so called "authority argument" is concerned, since you bring it up.....if the manufacturers thought RDM was better, they'd use it.

They could use ANY method they want, and after taking a lot of trouble to make a very accurate lathe, they could afford any test that was best, most representative, etc. It seems significant that the industry accepted test is TCT..... not because "they say so", but because they have settled on it as the best and most effective they can devise.... and because there are precious few arguments AGAINST it, (or in favor of RDM).

Dozens of measurements? I freely BRAG that I exaggerated....

It might only take 6 or 8 tries per measurement, to be sure the reading is the same..... and that you have actually reached the accurate max or min, etc, etc.

And .........you have a high and low to measure, and then mathematically average...........

I never said I hadn't tried it, you never asked..... I did try it, and rapidly decided to go back to TCT, which is far easier, and involves actually USING the lathe.

besides....

I have REPEATEDLY said that it "works" for the exact same measurement as TCT...... if you want to bother.

if you love it to death, go ahead and use it.... but do not make it seem like the "secret method that cures all ills, eliminates levels, that has been suppressed by the level industry"..... it ain't, and that has been proven.

I found it fiddly, and in the end inaccurate.

Rule #1 of metrology....... The best method is nearly always the one that involves the least measurements, and the measurements that are easiest to make accurately.

Compare TCT and RDM on that basis...... if you STILL prefer RDM, that's your privilege, and your own problem....

customcutter
05-21-2012, 09:46 PM
Hydraulic ram rods are not usually straight..

Not professing RDM, (which does not require a straight rod) just posted the runout after "roughly" leveling the lathe with a .0005"/in level. It improved by .002".

I plan on doing both RDM and TCM and comparing the results. At present I don't have any pipe to turn to do TCM.

I did put the "ram" in the tailstock however, and ran the indicator down the length of the side with each jaw of the chuck in the 9 oclock position. Deflection was less than .001" in each of the three positions.

thanks,
Ken

customcutter
05-21-2012, 09:53 PM
And most likely not perfectly round either (usually they are ground S355 + hard chroming or 42CrNiMo with a hard chroming). And when you chuck something 30" long for a couple of inches of gripping range, no matter what type of chuck you have, you will most definately get a runout.
It's as round as I need it. Less than .001" run out at the chuck. Chucked 3 times and measured 3 times.

thanks,
Ken

J Tiers
05-21-2012, 10:23 PM
Chucked 3 times and measured 3 times.



I can't resist....... was it still too short? ;)

customcutter
05-22-2012, 08:29 PM
I can't resist....... was it still too short? ;)

Yes, but only by .0001" on the last try.:D

thanks,
Ken

dian
05-23-2012, 10:58 AM
so, from experience, how much can you "twist the bed"? the alternative being to align the headstock.

for example, if i am getting a conus of 1 : 0.0002 (double that for difference in diameters), do i work on the jack screws? if i get 1 : 0.002, do i move the headstock?

Jaakko Fagerlund
05-23-2012, 02:00 PM
so, from experience, how much can you "twist the bed"? the alternative being to align the headstock.

for example, if i am getting a conus of 1 : 0.0002 (double that for difference in diameters), do i work on the jack screws? if i get 1 : 0.002, do i move the headstock?
Much depends on the exact construction of the machine, mainly its weight and weight distribution and if it is bolted solidly or just standing on its feet.

If the machine is very heavy and solidly bolted, you can twist it until it cracks in half from somewhere. If it is just standing on the legs, the weight pretty much determines how much it can twist/bend. But I'm sure you can easily achieve a great twist when trying hard :)

John Garner
05-23-2012, 03:54 PM
I see Rollie's Dad's Method (RDM) and the Two Collars Test (TCT) as half-brothers that, if correctly performed, provide generally-comparable results. Both methods attempt to characterize the difference between the radial distances from the headstock spindle's axis of rotation and -- depending on the test -- either a dial gage tip or a toolbit tip.

The TCT is very direct, but takes a lot more time and effort than RDM if the power hasn't been turned on yet. RDM substitutes the relative complexity of bookkeeping the results of several dial indicator measurements at half-spindle-rotation increments for the who-cares-how-many spindle rotations the TCT requires.

Assuming a solid setup, the most common stumbling block of RDM is the bookkeeping . . . which is only trying to find the spindle's axis of rotation -- at the center of the test-rod orbit -- at two different locations along the bed.

RDM does have a two-gage variant that's analogous to the two-dial-gage "spindle square" that's become so popular recently. It requires setting two dial gages on the cross-slide, on opposite sides of the test rod.

Taking my que from the textbook-writing professors . . . the rest is left to the reader as an exercise.

John

.RC.
05-23-2012, 04:32 PM
So what use are either methods if the headstock is not correctly positioned on the bed and the spindle is not in line with the bed ways?

Forrest Addy
05-23-2012, 09:50 PM
You goys with lathes who have doubts about their spindle will have to reconsile to the fact that no one test will prove a spindle alignment to a carriage motion. Two many interdependencies. Show me a guy who on the basis of one test averrs his spindle is dead nuts and I'll show you an example of over-confidence.

The only way I will warrant a spindle alignment is after leveling and alignment and I run a whole test card so that all variables are documented. THEN I can point to the relevent numbers on the card and the results of a turning test and state without fear of contradiction warrant the spindle axis is aligned witin 0.xxxx per foot and here are the results of the turning tests and the two collar tests and the alignment of the tailstock quill to the headstock.

If the machine is not under power I would get power to it if only by bolting a pony motor to a 2 x 12, run it from a home generator, and use it to drive the headstock pulley. I've done similar things exercising motor powered equipment sranded in defunct industrial buildings.

Home shop types can do similar without the paper trail of a contract fulfillment. In any case information and understanding precedes the pros and cons of alignment technique.

.RC.
05-23-2012, 10:49 PM
Forrest to check headstock alignment, don;t you use a proper test bar, and not having that, make sure the lathe is level first, then you take unsupported test cuts...


All this talk of Rollies dad and two collars.... Lets not forget that US made lathes are totally different to "everywhere else" in that US lathes the headstock sits on a V way and can not ordinarily be knocked out of alignment, while everyone else (well mostly everyone else) made their lathe headstocks sit on flat pads and the headstock is adjusted to suit...

J Tiers
05-23-2012, 11:31 PM
Forrest to check headstock alignment, don;t you use a proper test bar, and not having that, make sure the lathe is level first, then you take unsupported test cuts...

Which is exactly what the "TCT" IS....... take a fine cut over two rings, mic them to see if they are the same..... If outer one is bigger, H/S points to rear too much (or is very out of line vertically) if closer one is bigger, H/S points to front too much.



All this talk of Rollies dad and two collars.... Lets not forget that US made lathes are totally different to "everywhere else" in that US lathes the headstock sits on a V way and can not ordinarily be knocked out of alignment, while everyone else (well mostly everyone else) made their lathe headstocks sit on flat pads and the headstock is adjusted to suit...

Still works with either method, as long a you assume in both cases that the H/S is not way off in the vertical, tilted up or down. A gross tilt that way acts like a smaller front/back misalignment.

Sitting on pads, or on V-ways, unlikely to be tilted up/down eitehr way if it was made right, and not messed-with since.

if you add another set of measurements with RDM, you can check up and down tilt, if you wish. After he collars are the same size, you should be able to pass an indicator over them for up and down tilt with TCT..... seems that should work OK too.

.RC.
05-24-2012, 03:06 AM
A test bar in a head-stock is only for checking the MT taper - not the spindle alignment - unless the MT taper is accurately aligned to the spindle taper.



bull****... How do you think they align the headstocks at the factory.... Do they use Rollie's method? They will use a test bar and probably an expensive well made one...

If you use the two collar method or rollie's method and the headstock is not aligned, you could be twisting the crap out of the bed to get the lathe to turn parallel thinking that the bed is twisted, when it could very well be straight...

I have used the two collar method on my South Bend clone... Tiny little thing with only 600mm centres.... Worked a treat as that is what that method was thought up for... The lathe was not turning parallel, the headstock had to be straight as it sits on the V ways.. Put a slight twist in the bed (or straightened it whatever the case was) and it came back good enough in the test cut...

There is no way in hell I would use it on my 16" lathe other then as a practical final check... Nor would I use it on anything bigger then a South Bend 9"

alistair1537
05-24-2012, 03:40 AM
Oh, you guys!

J Tiers
05-24-2012, 08:34 AM
If you use the two collar method or rollie's method and the headstock is not aligned, you could be twisting the crap out of the bed to get the lathe to turn parallel thinking that the bed is twisted, when it could very well be straight...

I have used the two collar method on my South Bend clone... Tiny little thing with only 600mm centres.... Worked a treat as that is what that method was thought up for... The lathe was not turning parallel, the headstock had to be straight as it sits on the V ways.. Put a slight twist in the bed (or straightened it whatever the case was) and it came back good enough in the test cut...

There is no way in hell I would use it on my 16" lathe other then as a practical final check... Nor would I use it on anything bigger then a South Bend 9"

Of course, the TCT method is only INTENDED as a check of alinement.

In fact, RDM is only a check as well, albeit an over-complicated one IMO. But it is usually accompanied by instructions on how to "pretzelize" the machine...... THAT part is open to much question, for sure.

What you DO about what you find is entirely up to your better judgement, and the facilities provided on the machine for adjustment.

Lightweight lathes are not so easy to twist unless bolted down tight..... They are so light that their weight will NOT automatically twist the bed into whatever pretzel shape RDM (as usually presented) demands. You may end up loosening and tightening until it is sitting on three legs with the fourth up in the air.

That's an argument in favor of a good heavy lathe bench which will allow the bed to be shimmed and tightened with meaningful results.... Of course, any extreme remedies absolutely require a second look to see why such crazy stuff seems to be needed... odds are very good that it is NOT needed and you have overlooked something.

lazlo
05-24-2012, 09:53 AM
bull****... How do you think they align the headstocks at the factory.... Do they use Rollie's method? They will use a test bar and probably an expensive well made one...

LOL! :D Hey -- he's one of your's ;)

Lathe Alignment Test Bar 2MT High Precision Ground Bar (http://lprtoolmakers.auctivacommerce.com/LATHE-ALIGNMENT-TEST-BAR-2MT-HIGH-PRECISION-GROUND-BAR-P1422224.aspx)

http://acimg.auctivacommerce.com/imgdata/0/0/9/9/3/3/webimg/2757964.jpg

SmoggyTurnip
05-24-2012, 12:32 PM
Not professing RDM, (which does not require a straight rod) just posted the runout after "roughly" leveling the lathe with a .0005"/in level. It improved by .002".


How can ANY alignment method fix runout?

beckley23
05-24-2012, 06:45 PM
On page 18, Sep/Oct 2004, "Reconditioning a Lathe-Revisited", issue of HSM there is a lathe test card. For the most part the tests are performed in the order shown. The logic will be obvious. Test #22 is "Lathe must turn cylidrical with work mounted in the chuck"(I'm assuming this is "the two collars test"). The tolerances for; Toolroom lathes is .0008", Engine lathes ; 12-18" sizes .0015", 20-36" sizes .002". The bar is 12" out of the chuck and 4" D.
The same test/check is in every SB HTRAL book I've seen, it's in Connelly's "Machine Tool Reconditioning"(the whole test card is spread through out the lathe section).

The 4" D bar is a bit large for small lathes, IIRC, I used a 2" D for the 12" CK in the article, and a 2-1/2" D bar for the Series 60 in "Another New Toy" in the Monarch forum of PM.
Harry

sasquatch
05-24-2012, 09:24 PM
I'd just "BIN" the sucker, go buy a better one!!:mad:

Forrest Addy
05-24-2012, 11:18 PM
Just to clarify, the version of the two collar method I prefer is one where the two collars are machned separately if need be to within 0.0005" of the same size. The object here is to obtain two precisely sized reference diameters widely separated that can be scanned with a dial indicator mounted on the carriage. It's a means of quantifying the parallelism in the horizontal and vertical planes of the lathe spindle in respect to the carriage motion.

This way any number of readings can be taken as leveling and alignment progresses. If care is employed to not disturb the chuck or the two collar reference piece, the headstock can even be dismounted and adjustments made.

If you rely on turning tests alone eventually you will run out of material on the collar.

Success and consistancy of course depends on the condition of the lathe. If the saddle's fit to the bedways and the bedway's linearity is sufficiently degraded it may be impossible to secure consistant results. Then the decision has to be made to live with machine as-is taking time for every feature cut to sneak up on sizes by many cuts and hand finishing to size and finish/. Or to re-condition it, sell it down the river, or part it out/scrap it.

In answer to the other question about my using test bars. Hell yes, if one is available and it's straight. A good test bar makes the work so much simpler. However a good test bar costs $300 to $800 depending on size and quality. When the need comes the budget is scant and the lead time is long.

A test bar is a manufacturer's, re-conditioner's, and installer's tool. It seldom pays for a small shop to own one. A test bar is used once when the machine is first erected and then it sits on a shelf until you need it years later when the machine is surveyed for refurbish/replace. A test bar in its years on the shelf may become battered, rusty, even damaged; possibly modified into shop tooling, possibly lost. If a bar is not available and determinations have to be made, we have to resort to the expedients we are now discussing by their initials.

J Tiers
05-25-2012, 08:19 AM
Just to clarify, the version of the two collar method I prefer is one where the two collars are machned separately if need be to within 0.0005" of the same size. The object here is to obtain two precisely sized reference diameters widely separated that can be scanned with a dial indicator mounted on the carriage. It's a means of quantifying the parallelism in the horizontal and vertical planes of the lathe spindle in respect to the carriage motion.



Ah, perhaps THIS is the issue that makes people consider it so much MORE fussy and demanding.....

I prefer the "take a cut and measure" method. You will run out of material, but chunks of pipe are not hard to find. presumably you will always have a mic around (or if not, why is this matter even an issue?).

On the theory of "use once in a very great while", I simply make another test bar when needed.... A piece of pipe and a few minutes cutting the valley between collars takes care of another few years, and it is no issue sitting it on the shelf after use..... costs very little, works fine, tests the machine in actual use.

You CAN make a test bar with great effort, but you will still have the issue of re-seating it in whatever the holder is..... chuck, taper, etc. And then you have errors.

if you make your own at time of use, and never remove it until done, you KNOW it is consistent. No re-seating required, one less cause of errors.

Forrest Addy
05-25-2012, 08:56 AM
Ah, perhaps THIS is the issue that makes people consider it so much MORE fussy and demanding.....

I prefer the "take a cut and measure" method. You will run out of material, but chunks of pipe are not hard to find. presumably you will always have a mic around (or if not, why is this matter even an issue?).

On the theory of "use once in a very great while", I simply make another test bar when needed.... A piece of pipe and a few minutes cutting the valley between collars takes care of another few years, and it is no issue sitting it on the shelf after use..... costs very little, works fine, tests the machine in actual use.

You CAN make a test bar with great effort, but you will still have the issue of re-seating it in whatever the holder is..... chuck, taper, etc. And then you have errors.

if you make your own at time of use, and never remove it until done, you KNOW it is consistent. No re-seating required, one less cause of errors.

Which is why I default to the two collar method for one test of lathe condition. Yes there are a few others.

GadgetBuilder
05-25-2012, 01:16 PM
My view is all three headstock/bed alignment methods are in essence the same: if you have a precision test bar then you use it. If you don't have a precision test bar, you simulate it. With TCT you turn two accurate test areas on a bar and use them to simulate the precision test bar. With RDM you remove the error sources using arithmetic thus simulating a precision test bar. However it's done, the same information must be extracted from the test used. The goal remains: measure the deviation between spindle axis and bed ways.

I march to the beat of a different drummer in many areas and so it is with RDM. I consider John Wasser's paper on RDM to be a concept paper rather than a test plan ready for execution. The paper identifies error sources that make chucking a generic test bar differ from measuring a precision test bar fitted in the headstock taper. And he indicates how these errors could be compensated for mathematically. Finally, he describes how the results might be used to improve the situation.

In reducing the concept to practice, one need not (in my view should not) simply follow what he wrote. I believe the reason the error sources are identified is so the user can figure a way to minimize them. For example, providing a method to allow using a rod whose diameter isn't constant and removing the difference mathematically would be plain silly - I think it is included so people understand that rod diameter is critical to the measurement. Using an accurately ground rod with a major bend in it would be silly too. But, if the rod used has a slight bend the calculation should prevent it from affecting the result, where his logic on this seems reasonable.

The test bar will have some runout from chucking which is unavoidable. Runout at the far end can be minimized easily by snugging the chuck in increments, measuring the high point and pushing it down with your thumb, tightening more, etc. It's easy to get TIR within a thou at the far end. This makes it more closely simulate the perfect test bar we wish we had, making the mathematical corrections needed smaller. Then, set the indicator up for horizontal or vertical measurement and set indicator zero so the reading for runout at the chuck end goes equally above and below zero, making John's Near End Average = 0 so it can be ignored in the calculation. Now, the RDM calculation is reduced to adding the high and low readings at the far end together and dividing by 2. (This result is analogous to the TCT result except with TCT the result reads directly off the indicator since runout has been removed by machining.)

A detail John's paper ignored is test bar sag. All test bars sag, even precision test bars. A larger diameter test bar sags less. In all of the methods sag should be accounted for. Measuring the actual sag isn't easy so generally it is calculated and then used to adjust the vertical result.

John Wasser's paper suggests shimming the feet of the lathe to correct bed twist. He didn't say to check your common sense or experience at the door. It is reasonable to use whaterver means are available to ensure the bed isn't twisted before using any spindle/bed alignment method. Nor does his paper consider the effect of bed wear on the measurement so common sense and experience are needed there too.

Does RDM provide perfect results? Certainly not - although it looks like you're taking only two measurements per axis, setting indicator zero at the chuck end is really 2 more readings that enter into the calculation invisibly. So now there are 4 readings, each with a little error and if the errors don't cancel then it would be easy to be off half a thou. The ground test bar could have a diameter difference between the measurement points of a tenth since I can't measure better than that. The calculated sag in the test bar gets added in too and it's a calculated value which could be affected by the type of steel in the test bar. And so it goes -there is some noise in the result. It's random so sometimes it cancels and sometimes it adds. The question is, is the error in RDM greater than in other methods. And does it matter in a home shop - that is, there are some real world limitations imposed by Mother Nature when you try to use the results to adjust a lathe.

Straw man criticisms of RDM, things like twisting the bed into a pretzel, are constructed by taking Wasser's paper literally. Arguments like this suggest to me that people haven't considered the possibility that John Wasser's RDM is a concept paper with details left to the student.

As a student of RDM I find this thread very sad. The OP asked a question about RDM and was told it is a waste of time and that no competent craftsman uses RDM. Then things evolved to people apologizing for even mentioning RDM and on to people who fail to denigrate RDM feeling the need to qualify comments with "I'm not advocating RDM...".

If the RDM test is so fatally flawed as to be useless in the home shop then why not (unemotionally) post detailed reasons why so that students can learn?

John

Forrest Addy
05-25-2012, 04:53 PM
I'm not sure how bed twist and spindle alignment became linked. They are two separate problems and the order in which they are remedied is important. Cart before the horse: the bed is first adjusted into a near perfect plane. Using a precision level across the flats is almost always the simplest way to establish it. If one attempts to improve spindle alignment to the carrage motion (commonly expressed as t"take out the taper") by deliberately twisting the bed the carriage will bear on two diagonal wings.

All other checks and verifications are determined from a lathe bed only after it is in a plane (level). Only then can checks and adjustments of the fit of the saddle on the bed, spindle axis to the saddle motion, fit of the tailstock base to the bed, etc procede.

All too often people take a cut or two and discover some unaccountable taper and announce to the world the spindle is "out". Then they procede to tweak, shim, whatever to shivvy the spindle into compliance with their notion of a correction. There is a difference between an axis and a parallel tool path just as there exists tool build-up tool wear, thermal expansion, tool deflection and a half dozen other factors that affect the cylindriciity of a turned or bored surface.

As John mentions, there are to the home shop machine tool user three roughly equivalent ways to determine spindle axis alignment: test bar, RDM, and (newly coined) TCM. I have full confidence in the test bar and the TCM PROVIDED preliminary checks verify whichever used qualifies as a true representation of the extended sindle axis. I'm very skeptical of RDM because so many readings and calculations are involved, evolutions almost sure to introduce "observation" error. In theory it's no diferent from the test bar and two collar method. In practice, it's error prone unless heroic care and precautions are taken.

In the photos I've seen those who demonstrate RDM use a slender rod extending twenty or more diameters from the grip of a three jaw chuck and a 0.001" resolution indicator. Gravity attracts all objects. A 3/8 rod extending 7 inches droops 0.0004" from its own weight. That's the allowable spindle axis rise in one foot. Add another 20 grams from the gaginbg force of the indicator punger and the droop increases if applied on top or decreses if applied on the bottom.

A test bar the diameter of the spindle taper or a pipe having a 6 to 1 overhang is correspondinlty stiff and being stiff and the same diameter over the gaging surfae(s) they elinimate the need for averating and calculation.

Just stuff think about. Those of you locked into less critical work may scoff at such fuss and feathers and rightly so. It far exceeds your requirements. Sooner or later you will be called on to do something critical and I have set myself to prepare (actually, nag) the complacent for their next step in machine shop evolution. And to do that I need to raise undertanding of a machine tool's limitations and pass along the mental tools to correct or compensate for them them. Thus these tedious lectures of mine.

dp
05-25-2012, 09:25 PM
Imagine how long this thread might run if the OP had asked the following and gotten answers to his questions right away:

My question is, is RDM for aligning the headstock with the ways, and tailstock? Horizontal and vertical alignment by adjusting the headstock? Or is he talking about shimming the "feet" of the lathe in his discription to achieve alignment?

So - can someone please answer the following:


if RDM for aligning the headstock with the ways and tail stock?
is Horizontal and vertical alignment done by adjusting the headstock?
is he talking about shimming the "feet" of the lathe?

customcutter
05-25-2012, 09:43 PM
Imagine how long this thread might run if the OP had asked the following and gotten answers to his questions right away:


So - can someone please answer the following:


if RDM for aligning the headstock with the ways and tail stock?
is Horizontal and vertical alignment done by adjusting the headstock?
is he talking about shimming the "feet" of the lathe?


Beings I'm to OP, I'll take a stab at it.

Yes, in RDM he is describing shimming the feet of the lathe, not the headstock.

Yes, Horizontal and Vertical alignment can be done by adjusting the headstock. However, that would be last choice, after verifying other causes are not the problem.

Maybe. I think RDM in my case was used more as a check to verify headstock alignment with the ways and tailstock. I have learned that after leveling my lathe that everything came more into alignment. Also after setting for almost a week since leveling that it has "settled" and "runout, deflection, alignment, etc" whatever the correct term for it is has dropped from .006" before leveling, to .004" after leveling, to now .002" after settling for the past 5-6 days. I haven't tried actually aligning using RDM due to a lack of time and not having used a "machinist level" to level with. I'm curious to see what the numbers are after getting it finally "leveled".

thanks,
Ken (OP)

Forrest Addy
05-25-2012, 10:13 PM
The go-to machinist level is the Starrett 98. I use a 6" version but they come in multiples of 2" to a foot or more.

http://www.ebay.com/sch/i.html?_trksid=p5197.m570.l1313&_nkw=starrett+98&_sacat=0

It's accurate, handy and relatively low in cost. Further while it's graduated in 0.005" increments it can be read much closer than that provided you are willing to interpolate the bubble indications. The graduations are some distance apart and the bubble returns to the same indication when removed and replaced on the same slope.

In any case a half blind old fart like me can still eyeball a half or quarter graduation thus interpolating to just over 0.001" slope per ft.

If you pull a hair from your head (No hair? Rob one from SWMBO's hair brush) and tie it around the vial so you can move it along to align with the bubble allowing very consistent readings. If you reverse the level in its tracks and take readings both ways you can: a - calbrate the vial. and b - read the bubble consistantly (but with care to avoid parallax errors and the like) to 1/10 the vials graduations. That's 0.0005" per foot. Yes you have to be careful and yes its a PITA but my point is a Starrett 98 level if handled right can be a very accurate tool.

Can you do the same with a carpenter or a torpedo level? Not really, because they are commonly rated as 15 Arc minute levels and they have no graduatios besides the two marking the ends of the bubble.

So all is not lost if you dont have a master precision level costing $400 or even a clunky awkward cheapo import. You can do a good job with a gratuated machinist level if you know the slope each graduation represents. If will only take .longer.

Having said all that and run on forever over nuanced esoterica allow me one final comment. If your lathe is working OK then it's OK. Leave it alone and don't mess with it. If you're curious, and want to run some of the tests mentioned here go ahead BUT DO NOT suddenly feel a need to fix something that aint broke merely because you find it aint perfect.

.RC.
05-26-2012, 02:43 AM
Your headstock test does not tell you where the problem if any lies.

It could be a twisted bed, it could be a misaligned headstock... Without levelling the lathe first to discount a twisted bed your test will not tell you where any problems lie....

.RC.
05-26-2012, 04:22 AM
Who is having a knee jerk reaction?

I am just following principles of industry... Set up machine..trouble shoot any problems by reducing the variables in a controlled manner rather then use a method that can not determine where the problem may lie...

I could not care less what your expectations are as no doubt what is good enough for you is different to what is good enough for someone else, hence any advice given should be so that it can be applied by anyone...

Machtool
05-26-2012, 10:48 AM
Whois having a knee jerk reaction?
Don’t waste your time Richard. Keep in mind, they are just Tiffism’s. None of the above really happened. If it did, you would have multiple photo’s of it all ready, posted over and over ,every two weeks.

but it is on a fairly strurdy steel bench that is prettywell weighted (not bolted) down
Wouldn’t that be this , the really “strurdy” bench, you posted pictures of. Really strurdy.

http://i200.photobucket.com/albums/aa294/oldtiffie/Shop_and_tools/Shop_tools4.jpg

That’s the exact same lathe as AirSmith. (Do you blokes remember Air Smith.) If you won a packet of shim’s in a raffle. How the**** would you know how to place them, with a flimsy arrangement like that?

Then you have to laugh at the “weighted down”. Arn't those the 8 precision cylinder squares you drag out and photo shop, anytime, any one mentions precision square?

I believe this would be that fraudulent happy snap.

http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/Cylindermastersquares1.jpg

By your own omission your calling the name of that picture “cylindermastersquare” You don’t seem to store those “masters” all that well. But they do make great counter weights

Quick hand’s up here?. HAS any one ever seen a Cylinder Square that didn’t have centres in each end? Or is Tiffie the only one on the face of the planet, that has cylinder squares Not ground off centres?

If I decided to replace it, it would be on the trailer and "on its way"and a new lathe on its way within a matter of hours (same day)
Well thankyou Mr BHP - Billiton.

Would you seriously attempt to have anyone try to believe that you can have a used lathe pissed off in the same day and a new one replaced in the same day, Little own a matter of hours. Despite your imagination.

Given your constant ability to spew up pictures. Why are there no pictures of these machines coming and going? Crane trucks and all, Good action Pics. One on its way to scrap and a new machine coming in, all within that matter of hours on that trailer that you mentioned.

How lucky for you, now that you mention it. One of the best guys I’ve had through my door in the last 2 years, for the scraping classes is Simon L. He lives in Bittern, just around the corner from you.


He’s mad keen on having a re-union barbeque at his place in Bittern. There’s likely to be 2 dozen blokes. Some of the guys are flying in. Your welcome to join us for a burger.

Can we come around to your place after lunch ,your welcome to join us and you can do a sort of do a MasterClass metal working thing for us?

Phil.

dian
05-26-2012, 11:09 AM
what a glorious thread.

i grab the barbel shaped bar under the bench, chuck it up, make two cuts and measure. then i know whats going on, in less than two minutes, if i hurry up.

i wonder why aligning the compound has not been mentioned. i need to do this quite often. same procedure as above. i put an indicator on the side and after three cuts im done.

tiffie, how do you do this (you never put the test bar in the headstock taper)? same procedure as above?

GadgetBuilder
05-26-2012, 11:47 AM
As John mentions, there are to the home shop machine tool user three roughly equivalent ways to determine spindle axis alignment: test bar, RDM, and (newly coined) TCM. I have full confidence in the test bar and the TCM PROVIDED preliminary checks verify whichever used qualifies as a true representation of the extended spindle axis. I'm very skeptical of RDM because so many readings and calculations are involved, evolutions almost sure to introduce "observation" error. In theory it's no diferent from the test bar and two collar method. In practice, it's error prone unless heroic care and precautions are taken.


Forrest,

I think we agree that the bed/spindle measurement provides information to guide correction but the measurement method shouldn't be conflated with the correction method. We also agree that bigger is better for the test bar.

I am the student here, I appreciate the time you've taken and mean no disrespect. But I can't tell from your comment on the "many readings and calculations" whether you followed what I wrote in my tome at post 56: http://bbs.homeshopmachinist.net/showpost.php?p=771865&postcount=56

The implementation I suggest for John Wasser's RDM concept eliminates the majority of measurements and calculations he describes through choices during setup. The remaining user calculation is (hi+lo)/2 which seems similar to what is needed for TCM. You can find a more detailed description of my implementation on my site:
http://www.gadgetbuilder.com/Lathe_Align.html

From my perspective, RDM and TCM, as you described here:
http://bbs.homeshopmachinist.net/showpost.php?p=770807&postcount=3

Are virtually identical.

You set your indicator to zero on the left collar and read the error on the right collar. What I find most interesting is you say that, in the real world, a little runout is expected in the collars. To handle this runout you suggest averaging the values. In order to find these average positions I assume you calculate (hi+lo)/2 for each collar, just like RDM.


I submit that the RDM execution I describe is almost precisely what you describe for canceling runout. That is, you find the average position of the left collar and compare it to the average position of the right collar.

Thus, as I understand how TCM is done (in the real as opposed to theoretical world) you need the same readings I need for RDM. One difference seems to be that your runout is likely to be under a half thou while RDM runout is likely to be a thou or so. Near as I can tell, errors introduced by calculations or number of measurements would be identical.

John

lazlo
05-26-2012, 12:00 PM
Bless your heart! Lathe leveling is one of those religious items like "billet", aircraft aluminum, and whether to mash knurls :)

At this point, the OP is locked in a padded room, rocking back and forth and screaming :p

dian
05-26-2012, 12:49 PM
"You set your indicator to zero on the left collar and read the error on the right collar."

??? there wont be any error, unless something is really wrong. you measure the diameters.

(maybe you are talking about somebodys dad, who i have never met?)

GadgetBuilder
05-26-2012, 01:12 PM
"You set your indicator to zero on the left collar and read the error on the right collar."

??? there wont be any error, unless something is really wrong. you measure the diameters.

(maybe you are talking about somebodys dad, who i have never met?)

Did you read Forrest's description (as linked) of how he does the test using identical diameter collars?

customcutter
05-26-2012, 02:24 PM
At this point, the OP is locked in a padded room, rocking back and forth and screaming :p

Nope, not at all. I think I've actually learned quite a bit from reading the different replies. I was a little saddened by the "debate" that ensued, but it seems like there may be some coming together after all. I seems to me that they are both very similar. One uses any piece of rod you have handy, doesn't require an expensive test rod, and the other you make your own "test" rod.

thanks
Ken

dp
05-26-2012, 04:50 PM
I was a little saddened by the "debate" that ensued,

The "debate" does make me chuckle at times because each debater in turn is trying to put a better finesse on what they understand to be the question you didn't ask but should have :) while not leaving the chorus of voices critical of the RDM. Your original question is perfectly acceptable but did not allow for the larger expansion filled out from their lifetime well of prejudices, training, and experience.

Ultimately all the RDM is doing is finding the actual spinning center of each end of a rod and observing that it is or is not an axis that is parallel to the ways. Nothing more. You can do the exact same thing with a chucked laser that is aligned with the spinning axis of the headstock (think tru-set laser) and the results are the same.

It won't tell you how much the alignment is out and is probably not a goal of Rollie's dad. It will tell you only that it is out of alignment. It is a very fast simple tool to tell you that you need or do not need to use better tools to actually align your lathe.

It is in the same category as Frank Ford's tail stock alignment trick. It doesn't tell you anything precise, only that you may wish to act further on what the trick tells you using more precise tools and methods.

http://www.frets.com/HomeShopTech/QuickTricks/TailstockAlignment/tailstockalignment.html

Done often enough you will develop the experience needed to properly understand what the simple tests tell you.

Rollie's Dad's method rocks. So does Frank Ford's trick.

dian
05-27-2012, 01:08 PM
gadget, i was trying to make a point. the point is: dont complicate what is very simple. (btw, there are no "identical diameter collars", never seen them and never will.)

so, for the hell of it, i went to my big lathe today and checked it. grabed the barbell, chucked it up, made the cuts. it was out by 0.01 mm over 150 mm, no wonder, lathe sits on wood.

so, put a 0.2 mm shimm under it, cut. still out. put another 0.2 shimm under it. cut. lucky. as good as it gets, +/- 0.001 mm.

what do you figure, how long did it take? (about one "thenth" of the time to read and digest your quote.)

philbur
05-27-2012, 01:27 PM
If your appropriately selected measuring equipment doesn't detect a difference then for practical purposes the collar diameters are identical. Splitting hairs adds nothing to your argument.

Phil:)


btw, there are no "identical diameter collars", never seen them and never will.

J Tiers
05-28-2012, 11:22 PM
You set your indicator to zero on the left collar and read the error on the right collar. What I find most interesting is you say that, in the real world, a little runout is expected in the collars. To handle this runout you suggest averaging the values. In order to find these average positions I assume you calculate (hi+lo)/2 for each collar, just like RDM.



Well, I DO NOT do that.......


I chuck it up, turn a tad off if it is 'winking' at me, and then when I have complete surfaces, I measure the two diameters.

ONE measurement per collar, and it is a "comparison", I have NO interest in the actual size.

When correct, both are the same. I already posted the conclusions for the case of them NOT being the same.

No long slender rods, bugger t'droop for larger diameters (it isn't much, and it affects nearly nothing), and a direct check of the lathe "in action" the same as when I USE it....

I am a great one for direct checks..... not "implied" results, or checks of the system in a "theoretical" mode..... Use it as you will actually do, and check results is generally best.

When that is impractical, do the closest thing.

My thought is that TCT (or TCM, whichever you want to call it) is simple, direct, and involves the fewest possible settings, zeroings, or assorted additions, subtractions, and the like.

You-all start to sound like some hot-sauce freaks, arguing over a few Scovill numbers difference.

if you want to use RDM, knock your socks off.... I believe that it has more measurements and settings, and is a "one step removed" test, causing it to have more error sources than the "re-cut when used" TCT/TCM.

Forrest's "no cut used" two collars bar is essentially a regular test bar, reduced to two "rings of accuracy"...... So I would lump that idea under "test bar" instead of TCT/TCM.

GadgetBuilder
05-29-2012, 11:34 AM
My thought is that TCT (or TCM, whichever you want to call it) is simple, direct, and involves the fewest possible settings, zeroings, or assorted additions, subtractions, and the like.

...

if you want to use RDM, knock your socks off.... I believe that it has more measurements and settings, and is a "one step removed" test, causing it to have more error sources than the "re-cut when used" TCT/TCM.

Forrest's "no cut used" two collars bar is essentially a regular test bar, reduced to two "rings of accuracy"...... So I would lump that idea under "test bar" instead of TCT/TCM.

Jerry,

First, let me give you my perspective and a synopsis of where I think this thread is presently.

Apparently I have become the "vocal adherent" of RDM that Forrest referred to in post 6. In this capacity at post 46 I have attempted to point out that John Wasser's document is not a plan for execution of RDM and that it conflates measurements with correction method leading to confusion. I have linked to information on my site that is much closer to an execution plan for RDM, close enough so readers should be able to execute it.

Forrest is a no BS guy so he has posted an execution plan for TCM with detail similar to that for RDM on my site. With this as background we each understand the other's execution plan. So, we are able to "engage" and we're discussing the relative merits of the two approaches along with their differences and similarities. I've learned some things from the discussion and must tweak my execution plan accordingly. What I have learned so far concerns second order effects, the basics of my execution plan need not change -- but I am awaiting Forrest's response to my latest post which could, of course, change that. End of synopsis.


I would be more than happy to learn from you also. In order for this to work out you need to put your execution plan "out there" as both Forrest and I have done and it needs to be at a similar level of detail. It also needs to be "real world" as Forrest's plan is -- chatter, tool pressure, finish, etc. -- concerns applicable to the HSM. This puts stakes in the ground so everybody can understand what's being argued. If you'd like to do this, start a new thread and link to or include a description of your detailed execution plan, link to my post 46 here, and explain why my approach is deficient. I'd be happy to participate.

Another thing I've learned from this thread is not to respond to drive-by one or two line posts. You'll need to make step by step arguments because I'm not a machinist so things that are obvious to you may not be obvious to me. Forrest also raised the "more measurements" issue which I believe I addressed in my last post to him; in your new thread perhaps you can share where you think I went wrong when I showed that it only takes (hi+lo)/2. The first argument I will make in your new thread is that you need to separate horizontal and vertical errors and that isn't easily done using just the collar diameters - I expect you need to make indicator readings in addition.

I will not engage further on your TCM method in this thread since I'd like to keep Forrest's argument separate from yours. In fact, it would be helpful if you and Forrest could settle which variation of TCM is best to minimize confusion.

Discussions like this are interesting when the emotion and BS are removed, sometimes the other guy's perspective forces you to change yours. With luck, you both learn more about how Mother Nature is running things.

John

We can be absolutely certain only about things we do not understand." Eric Hoffer, "The True Believer"

dp
05-29-2012, 11:53 AM
It helps quite a bit to keep answers in scope with the original question, too, and which, by the way, is:

My question is, is RDM for aligning the headstock with the ways, and tailstock? Horizontal and vertical alignment by adjusting the headstock? Or is he talking about shimming the "feet" of the lathe in his discription to achieve alignment?

In my opinion the answer to the first question is no, the RDM method has nothing to do with aligning a lathe - it tells you only that you may need to align your lathe.

One can choose to minimize the errors revealed by RDM by shimming but that is not the same as aligning things because RDM is self-referencing.

GadgetBuilder
05-29-2012, 12:11 PM
dp,

I believe I could answer the OP's question and my answer would differ slightly from yours.

However, in post 6 it was stated that no competent machinist would use RDM. I use RDM so I took this to mean that I am incompetent. If I am incompetent it would be irresponsible to offer advice in my area of incompetence.

The problem with being incompetent is that you can be so incompetent that you don't realize you're incompetent.

See: http://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect

In my case, the jury is still out on that...

John

J Tiers
05-29-2012, 07:05 PM
Jerry,


Forrest is a no BS guy so he has posted an execution plan for TCM with detail similar to that for RDM on my site. With this as background we each understand the other's execution plan. So, we are able to "engage" and we're discussing the relative merits of the two approaches along with their differences and similarities. I've learned some things from the discussion and must tweak my execution plan accordingly. What I have learned so far concerns second order effects, the basics of my execution plan need not change -- but I am awaiting Forrest's response to my latest post which could, of course, change that. End of synopsis.


I would be more than happy to learn from you also. In order for this to work out you need to put your execution plan "out there" as both Forrest and I have done and it needs to be at a similar level of detail. It also needs to be "real world" as Forrest's plan is -- chatter, tool pressure, finish, etc. -- concerns applicable to the HSM. This puts stakes in the ground so everybody can understand what's being argued. If you'd like to do this, start a new thread and link to or include a description of your detailed execution plan, link to my post 46 here, and explain why my approach is deficient. I'd be happy to participate.

Another thing I've learned from this thread is not to respond to drive-by one or two line posts. You'll need to make step by step arguments because I'm not a machinist so things that are obvious to you may not be obvious to me.


In other words.... if I might paraphrase your ever-so polite blow-off...............

"You are a G-D thread hijacker, so go tickle yer backside BY yerself someplace else where I don't need to see your name, and do it now, just cuz I said so!"

Thanks muchly..... but NOT so much.....

1) What I post about TCT (you call it TCM) is as relevant as what anyone else posts about it here. So I'll keep on, if I decide anyone else cares/...... you evidently do not.

2) DRIVE-by posts? I have been out of town, doing good works and ignoring this infested site. I STILL have probably 4 posts in this swamp, and I DID post sufficient method explanation for the average person.

3) NO I do NOT feel like going away to some other thread which you can and will ignore...... See point #1.

4) Thanks for the invitation to become irrelevant, but I'll pass.......