PDA

View Full Version : Too much accuracy



loose nut
02-06-2010, 07:38 PM
Today, out in my shop, I was boring out a piece of 1/4" plate for a shrink fit onto another piece.

Recently I have purchased a set of digital Mics, with a resolution to tenths and I have had a hard time remembering that there is 4 decimal places instead of the 3 that I 'am use to.

So while I was measuring the bore I read the ID as about 70 thou when it was really 7 thou and change (damned extra digit). Needless to say after taking another roughing cut it was a good rattling fit and being Sat. afternoon I can't get a replacement piece of steel.

The best laid plans of mice and machinist often.........

John Stevenson
02-06-2010, 07:46 PM
A few years ago a local company to me replaced all the Heidenhain DRO's on their machines from the old 3 1/2 digits [ they read in 0.0005" steps ] with full 4 digit readouts that read in tenths.
to conform to BS9000 and the relevant paper trail.

I bought a couple of the old but working units off them.

Later when I called in I noticed that every one of the new readouts had a band aid stuck over the last digit because they were driving the operators mad with the constant flicker.

So much for progress............

.

lenord
02-06-2010, 07:48 PM
At least you have a good excuse for messing that up.

I've bored a hole too big, on a lot more expensive parts, with no more excuse than a "brain fart"..........

Lenord

Lew Hartswick
02-06-2010, 07:50 PM
to conform to BS9000
.

I like that alphabetic prefix. :-)
...lew...

Weston Bye
02-06-2010, 09:10 PM
I have to confess that I have been pathologically unable to cope with BS9000, TS1234blabla, or whatever the current fad is. I hold unconcealable contempt for a system where completion of paperwork takes precedence over actually producing an actual moneymaking product. My boss understands this defect in my character and has taken pains to insulate me for over 10 years from the depredations of the QS/TS auditors and the nefarious process. One result is that I am the only engineer in the plant who has an office rather than a cubicle - where they can close and lock the door.

gregl
02-06-2010, 09:17 PM
I have to confess that I have been pathologically unable to cope with BS9000, TS1234blabla, or whatever the current fad is. I hold unconcealable contempt for a system where completion of paperwork takes precedence over actually producing an actual moneymaking product. My boss understands this defect in my character and has taken pains to insulate me for over 10 years from the depredations of the QS/TS auditors and the nefarious process. One result is that I am the only engineer in the plant who has an office rather than a cubicle - where they can close and lock the door.


Weston, you're a lucky man. But which side of the door is the lock on, and did they put padding on the walls?

Weston Bye
02-06-2010, 09:18 PM
They always let me out at the end of the day. No padding, but they let me keep all my toys (bits of machinery, parts, contraptions, creations, etc.) there.

nheng
02-06-2010, 10:33 PM
I have to confess that I have been pathologically unable to cope with BS9000, TS1234blabla, or whatever the current fad is ...

Weston, we must be distant relatives or something. Our ISO auditor is always diagonally opposite wherever I am in our plant. In years gone by, I made it a point to take vacation time on the day of the audit and funny, no one objected to that ;)

ISO, CE, IEC, LEAD FREE, ROHS, WEE, and next ... REACH. The US has fallen flat on its corporate face by not retaliating against this foolish nonsense in any way, shape or form. REACH in particular, should be DOA.

One of the most disturbing things about this stuff is that there are some people who actually enjoy turning it into an essential part of their life. We could have easily been exempted from ROHS because of the class of product we make. One of the paper lovers managed to get us sucked into it instead. Now we're heading toward REACH and that same sucking sound is there.

Den

Carld
02-06-2010, 10:43 PM
Yeah, I hate those extra places. Hmmm, now where the heck did I leave my last place and what place was it. :eek:

Yep, having to deal with four places on a DRO, caliper or mic can be troublesome.

Ken_Shea
02-06-2010, 10:52 PM
On the mill DRO, I cant seem to stop chasing that last .0002 increment when anywhere close would be good enough, a lot of time is wasted on that un-needed precise readout.

Set the distance with the DRO, tighten the gibbs, oops, that moved the DOR by .0002, must correct that, compensate, ahh all is good to go now, gibbs are tight and the DRO reads .0000, what a waste of good time!

oldtiffie
02-06-2010, 10:55 PM
Is it really all that hard to locate the decimal point and to work left and right from there?

Maybe you need to be "de(re)-programed" so that you can (will?) "unlearn" some stuff so that it can (you) can be "up-dated" wit a new set of reactions.

A lot of this is "conditioned reflex(es)" stuff which might put you right up there with "Pavlov's dogs".
http://en.wikipedia.org/wiki/Ivan_Pavlov

loose nut
02-07-2010, 09:52 AM
You (I) may be right but can (will) we do anything about this problem (behavior). Conditioning (brainwashing) is had to undo (deprogram).

At least on my DRO I can switch from 4 to 3 decimal places if I wish and the problem goes away.

mochinist
02-07-2010, 09:59 AM
Is it really all that hard to locate the decimal point and to work left and right from there?

I'm with tiffie on this one

Paul Alciatore
02-07-2010, 11:23 AM
You (I) may be right but can (will) we do anything about this problem (behavior). Conditioning (brainwashing) is had to undo (deprogram).

At least on my DRO I can switch from 4 to 3 decimal places if I wish and the problem goes away.


So you drop the land mine and just let it lay there? OK, I'll ask the question.

Which brand is your DRO?

Better question, do any brands allow you to set the precision displayed? 2, 2.5, 3, 3.5, 4 places? Or any CNC software?

gnm109
02-07-2010, 12:39 PM
I recently installed a new Mitutoyo 2-Axis DRO on my new to me Webb 4VH Mill. This DRO has four places and it's set up so that the 4th digit is always "5" ( .0005). That's fine with me since that's all the accuracy I would ever need.

I looked in the manual but I can't figure out any way to make it read the 4th digit any finer, say .0001, .0002, .0003, etc. I wonder if that can be done?

The manual, although printed in excellent English, seems to be somewhat over my head. LOL.

loose nut
02-07-2010, 02:01 PM
So you drop the land mine and just let it lay there? OK, I'll ask the question.

Which brand is your DRO?

Better question, do any brands allow you to set the precision displayed? 2, 2.5, 3, 3.5, 4 places? Or any CNC software?

It's a Fagor DRO, Reads down to 0.0002 but I usually have set in the 3 digit mode which is accurate for most of the things I make and yes reading the decimal point can be a bitch if you are used to something different. It does require retraining of the mind.

Rich Carlstedt
02-07-2010, 02:05 PM
The forth decimal is typical folly.
Its like the MPG rating on your car.
There is no end to those who feel they can do better machining by having the forth digit, Let alone read in Tenths !
The DRO marketers take advantage of that
Give me a break..
It is incredibly naivete to think you can hold a tenth , or tenths, on almost any machine when you have precision bearings with 1.5 tenths runout.
Its naive to think that temperatures have no effect on your work or the scales !
I worked for many years on Dies , where the tolerances were in tenths in many cases, but DRO's never got it for us..and never will.
The "fourth" number also have caused more scrap or rework then anyone admits , much as mentioned in the beginning of this thread

The DRO's in my shop ( like I did at Work) have black electrical tape over the forth digit, with a horizontal slit 1/8" high and 3/8" long in the middle
A zero reading is blank, and a 5 reading becomes a dash -
Not sophisticated, but it sure eliminates the errors and false readings, and is there if I need to know what it says.

The DRO makers could do wonders, if they made the tenth read out a smaller size, like a exponential number

Weston, you and I are from the same mold.
"paper does not complete a part, a man does"
Been there , done that
Rich

juergenwt
02-07-2010, 02:34 PM
45 years as a Tool and Die Maker working on dies, fixtures, gages and tooling and stayed away from my 0.0001 indicator. I don't think I used it once.
Used a " Last Word" 0.001 indicator all my life and told all my apprentices to put away those 0.0001 indicators. You can read within 0.0001 on a 0.001 indicator and it will not drive you nuts. Indicators are only good for comparing. You need to set gage blocks on a planer gage ore use a Cadillac Gage to set a dim. There is a formula to calculate the actual movement of the indicator based on the diameter, length and angle of the point. It is useless since in most cases the ball on the point will be worn flat.
Micrometers - ditto.

J.Ramsey
02-07-2010, 02:43 PM
I looked in the manual but I can't figure out any way to make it read the 4th digit any finer, say .0001, .0002, .0003, etc. I wonder if that can be done?

The manual, although printed in excellent English, seems to be somewhat over my head. LOL.

Go to the section 4.2 about setting parameters, setup data code 1.

That will make it .0002, I tried it and switched back after about a half hour of chasing my tail.

The Mit manual is written for those that understand their techno babble, which is why I had to have a techie friend explain it to me.

John Stevenson
02-07-2010, 03:01 PM
45 years as a Tool and Die Maker working on dies, fixtures, gages and tooling and stayed away from my 0.0001 indicator. I don't think I used it once.
Used a " Last Word" 0.001 indicator all my life and told all my apprentices to put away those 0.0001 indicators. You can read within 0.0001 on a 0.001 indicator and it will not drive you nuts. Indicators are only good for comparing. You need to set gage blocks on a planer gage ore use a Cadillac Gage to set a dim. There is a formula to calculate the actual movement of the indicator based on the diameter, length and angle of the point. It is useless since in most cases the ball on the point will be worn flat.
Micrometers - ditto.

Yup don't bother with tenth's, use thou's then if you need more accuracy move to Canada where it's temperature controlled all year to -45 and work in Microns.

.

oldtiffie
02-07-2010, 03:52 PM
45 years as a Tool and Die Maker working on dies, fixtures, gages and tooling and stayed away from my 0.0001 indicator. I don't think I used it once.
Used a " Last Word" 0.001 indicator all my life and told all my apprentices to put away those 0.0001 indicators. You can read within 0.0001 on a 0.001 indicator and it will not drive you nuts. Indicators are only good for comparing. You need to set gage blocks on a planer gage ore use a Cadillac Gage to set a dim. There is a formula to calculate the actual movement of the indicator based on the diameter, length and angle of the point. It is useless since in most cases the ball on the point will be worn flat.
Micrometers - ditto.

I am with you on that juergenwt.

My everyday indicator is a 0.01mm (~0.0004") one and so "halving" it for "2 tenths" or "quartering" for "1 tenth" is quite easy.

My calculators all read to multiple points after the decimal point but I mentally reduce it to the accuracy I need - 0, 1, 2, 3, or 4.

That applies whether I am working in metric or inch. Its just a mental adjustment to put myself into either inch or mm mode. I can do it quickly and easily - both ways - both before I start and during a job.

DRO's are or can be a PITA as relying on the DRO for position of say the mill table "X" reading relative to the apron is fine but there are a couple of "traps":

1.
the direction of "coming onto" a job with the cutter can be neglected and if it is got wrong the screw back-lash and end-play has not been "taken up" and if the "X" clamps are not applied, or not applied tightly enough, the cutting load may move the table (hence the need for zero back-lash and end play in bi-directional CNC operation) and then a real problem will exist.

2.
Slack, clearance or wear in an "X" slide will be at 90* to"X" - ie in the "Y" direction but will not be detected by the "Y" DRO. Table movement in "Y" due to cutting load or clamping in "X" will not show up on the "Y" DRO.

3.
Removing lead-screw back-lash and end-play does not compensate or reduce the effects of dove-tail wear as unless you have a perfect dove-tail - which is all too often not the case. The gibs are set for "best fit" which is nothing more than a compromise between "too tight" and "too loose".

So, in short, DRO's very accurately show the relative movement between the fixed and sliding parts on the parts on which the DRO is mounted,but they may not necessarily show the total or correct relationship between the tool and the job.

If I really am fussy about a relationship between a job and a cutter I will use a dial indicator as that will - more often than not - reduce or cancel out any "table" or "slide" errors that a DRO will not or may not be able to detect.

There are a lot of "phantom" sizes with DRO's that are not easily recognised.

If I am getting into "two tenths" territory, I always ask myself how that happened and if it is really necessary and go "back over" the job to see if it is really needed. It isn't needed more often than not. If it is needed I "tighten up" my procedures and deal with it. If it isn't needed, I don't use it.

As always - with me at least - the final cuts and the final sizes are checked with a micrometer.

As previously, my 0.01mm (~ 0.0004") micrometer does the job very well and while it has the accuracy of an "inch" "tenths" micrometer it has none of the "tenths vernier" clutter.

So, no matter how accurate the DRO is or how many decimal points it reads to, it is the relative positions between the cutter and the job that counts.

Without getting back to the old inch vs metric argument, "half a thou" will show up on a DRO as XXX.XXX5" (4 decimal places) but as 0.01mm is ~ 0.0004" it will show up on the DRO as XXX.X1mm (2 decimal places). Try it on your digital caliper.

CAD, or AutoCAD at least, can set the number of decimal points as could my HP41 series calculators. My HP48GX calculator probably has the same feature but its a PITA to set so I leave it at its default setting and just mentally "clip" it to the number of numerals after the decimal point that I need.

DRO's are a very useful tool but they do not solve all of the problems.

There is still a fair bit of effort and intelligence required of the operator/machinist as DRO's are not fool-proof.

MuellerNick
02-07-2010, 04:13 PM
My everyday indicator is a 0.01mm (~0.0004") one and so "halving" it for "2 tenths" or "quartering" for "1 tenth" is quite easy.

Dial indicators generally do have a backlash of 0.5 to one graduation. Also, the overall error is within that range.


Nick

Scishopguy
02-07-2010, 04:17 PM
Besides that, the more zeros that they stick in the dimensions on that print gives you more chances to miscount them and screw up the part.:( Sometimes I think that the bean counter mentality extends into other areas of our life. You know, that mindset that thinks that if something to three places is accurite then something called out to four places HAS to be much more accurite. I think it is a fundimental inability to deal with the real world.

This goes along with the misguided idea that all jobs must be held to the absolute highest accuracy possible. Sounds nice but reality usually comes in the form of time constraints and bites them in the butt.

Just my $0.02

oldtiffie
02-07-2010, 04:47 PM
My everyday indicator is a 0.01mm (~0.0004") one and so "halving" it for "2 tenths" or "quartering" for "1 tenth" is quite easy.


Dial indicators generally do have a backlash of 0.5 to one graduation. Also, the overall error is within that range.


Nick

Thanks for the "heads up" Nick as I over-looked including that.

I always "take up the slack" on an indicator and try to have it indicating in the same direction.

MuellerNick
02-07-2010, 04:54 PM
I always "take up the slack" on an indicator and try to have it indicating in the same direction.

Then it's OK.
I suppose you know how good the repeatability of your tool and setup is.

You know, some people are telling tales about accuracy of $whatever. And if you ask, they do have a 9.99 dial indicator from ... YouKnowHere.


Nick

loose nut
02-07-2010, 05:25 PM
Looks like we are going to have to go back to using "buttons" and setting up the job on a surface plate but then we would use our "fake Blake" indicators to dial in the buttons and screw up the job.:( :o :confused: :eek:

darryl
02-07-2010, 05:43 PM
Hey, I have a great idea- if you need to work to tenths, get a dial indicator that will read to tenths! (drum roll) Seriously, I'd rather have a dial indicator than a dro. Maybe if they made an electronic scale that emulated a dial indicator, that could work. I hate ambiguous numbers jumping around- same with the electronic voltmeters- I'd rather see a needle pointing at a scale than a set of numbers that won't stabilize.

But on the subject of too much accuracy, I need some washers for the screws holding the back on my washing machine. I think I'll machine some so they aren't so sloppy :)

John Stevenson
02-07-2010, 06:08 PM
But on the subject of too much accuracy, I need some washers for the screws holding the back on my washing machine. I think I'll machine some so they aren't so sloppy :)

Good idea then you can make then bigger than the damn screw head.

Just took delivery of some buttonhead cap screws, standard says head is 2D.

Not these, 1.8D

.

oldtiffie
02-07-2010, 08:36 PM
I have no objections at all to DRO's - they are excellent if used correctly.

I have full sets for my HF-45 and Sieg SX3 mills - I just haven't had the need to install them yet.

DRO's do "trap" people into the errors as I mentioned earlier.

They also tend to have people work (or attempt) to work to a couple of tenths when a couple of thou - or more - is more than adequate.

Drilling clearance holes on a PCD is a good case in point as the positioning and finished size of the holes are not all that important. In many cases it would be easier and faster to mark it out on the marking table (NOT the "surface plate"), centre-punch it and drill it on a pedestal drill. If I was going to drill it with a DRO, I'd drill the centre or spotting drill with the same drill on the mill with the DRO and as all subsequent drills would follow the centre/spotting drill, I'd finish drill it on the pedestal drill. But I'd also consider just using a rotary table and centre the RT under mill quill, use the DRO to off-set the pitch circle radius and then index using the RT to drill the holes. I could index it just by using the hand-wheel and the index marks on the RT table. My 8" RT is a quick index as well so its just a matter of latching and unlatching as any sub-multiple of 12. All of them are pretty accurate.

There is no real reason why various methods of setting and indexing can't be used together - no need to use the DRO's all the time.

DRO's and CAD are just made for each other. Just get the co-ordinates for "X" and "Y" ("Z" too if you want to) in CAD and record them and use them with your DRO (a sort of "manual CNC").The base or reference or "zero" can be set to the same feature on the job and in CAD and then extract/record it and then apply it on the DRO's for the job and you are there.

DRO's will NOT make anyone a good or better machinist on their own any more than a "high quality" mill or lathe will - but they will certainly help- you along the way if you use a bit of common sense - the corollary of which is just as as true though - use them unwisely and they will really "bite" you and/or the job - as well as your ego and self-esteem.

Ken_Shea
02-07-2010, 09:26 PM
Who would of thought from the OP :D

IMO:
1) DRO's are the best thing anyone can put on a mill and will hands down be the most used tool used on it.

2) DRO's do not trap you into anything, it's sole job is to relate table and/or head position, it's job is not to correct for worn out equipment or instruct me on proper machining technique.

3) Chasing precise reading's is my fault and not some inherent habit from using them. Notice, in a earlier post, I said chasing, not machining in those same precise readings.

4) In spite of that wasted time chasing, will still save gobs more time then one would ever spend chasing in over all use.

5) DRO's are not a replacement for a dial indicator any more then a Dial indicator is a replacement for a DRO.

6) Don't any of you try and sell me on the idea that you never wasted time mis-reading a dial, lost count, pushed the wrong button on a calculator to get your dial rotation figures, even this wasted time chasing is moot.

Besides, I'm pretty fast at chasing anymore ;)

danlb
02-07-2010, 09:35 PM
While I agree that the extra digits are not always wanted, I don't find them that much of a hassle. If I have only 3 significant digits, then I only know that I'm within .001 of my desired point. With 4 digits. I can decide if I want to go over or under my desired dimension.

The DRO does not make me a better machinist. BUT..... It cuts down on the number of times that I get near the end of a cut and find myself wondering if I missed counting a turn. So it makes it a bit more enjoyable.

Dan

gnm109
02-07-2010, 11:20 PM
Go to the section 4.2 about setting parameters, setup data code 1.

That will make it .0002, I tried it and switched back after about a half hour of chasing my tail.

The Mit manual is written for those that understand their techno babble, which is why I had to have a techie friend explain it to me.


Thanks, I'll check it but after reading this thread, I probably will just leave it alone. Thousandths of an inch are plenty good for my stuff.

darryl
02-08-2010, 12:04 AM
How do you know if you've hit say 4.0005- could be 4.0027 for all you know, or 3.9968. I just found not long ago that my digital caliper is out by enough that it makes reading or working to tenths a wasted effort.

It might be that for most of us, it's seldom important to get the overall length of a part exactly right within a thou or less, but it would be more important to be able to fit a bushing properly, or create the right geometry to ensure a press fit for a stud for example. Most often that's going to mean working to something closer than a thou, and probably of even more importance- knowing how to interpret an inside and outside reading with any particular caliper or measuring instrument. You might carefully machine a shaft to 1.0005, only to find that the bore that it's supposed to fit in (that you also machined carefully to size, say 1.0000, is actually 1.0017.

Are you working to tenths as read on your gauge when you're fitting something? Or do you put the gauge away and rely on a different method of ensuring that half-thou interference fit, or that half-thou running clearance for the cam on your model engine-

I work to tenths quite often, but usually only where it matters. Most of my work would not win any beauty contest- lots of your guys work would. When I do machine something to a close tolerance where it isn't needed, I consider that practice, and I try to gauge (sic) how much faster I can do that now than I could before. If it's time consuming, and it isn't needed, I don't do it. If it's not time consuming, and it's a matter of twisting that handcrank to be right on the mark, or being happy just to see that it's close- why not hit the mark.

By the way, in the last hour I've managed to turn out two of those precision washers for my washing machine cover- :) Hey, John- you in a hurry for those washers for your bolts?

oldtiffie
02-08-2010, 01:48 AM
A little thought provoker.

Put an accurately ground cylinder the same size as your end mill in the collet in the collet adaptor in your mill spindle and projecting say 2". Now use a good test dial indicator (TDI) to measure the total indicated run-out (TIR).

I will assume a perfect end mill for the moment.

If the TIR at the top and bottom of your test cylinder is zero you are doing very well as all the cutter will cut equally on all teeth and the (side) face it cuts will be parallel to the mill spindle axis (which is presumed to be correctly and accurately trammed).

If the TIR at the top and bottom is say 0.001" (not unusual) this is not so bad. This too will cut a face that is parallel to the mill spindle axis but only one or two at most of the teeth will be cutting and at least one tooth may be rubbing (not cutting) and so wearing unevenly.

If the TIR at the top is say zero and is 0.001" at the bottom (2" away) - (not unusual either) - all of the teeth at the top will be cutting evenly but as the faces of the cutter are now describing a cone instead of a cylinder and only one or two of the bottom teeth will be cutting with one rubbing as before. In that case the "taper" or"out of square" will be 0.0005" per 2" for each face cut. The "taper" will be "cut in more" (than the top of the cut will) at the bottom of the cut.

Now if two opposite sides of the job are cut the taper will be doubled into a shallow "dove-tail" and the difference between the top and bottom of the opposing faces will be 0.001"/2" length of cut. On opposing external faces the bottom will be less that at the top. For opposing internal faces the bottom will be "wider" than at the top faces. For compounded internal and external faces the error due to the taper will be additive and doubled.

So all the "accuracy" of the DRO is thrown into serious doubt as the micrometer does not agree with the DRO.

In that last example, I have presumed that the end mill itself is not tapered (the larger or smaller sizes can be at either at the top or bottom of the cutter edges) and that the cutter will duplicate the test piece. It may not if the collet is not in precisely the same location in the adaptor as it was when the test piece was indicated.

Now how many do - or can - measure the TIR on the sharp edges of the cutter and get an accuracy comparable to that on the test cylinder?

And how will a DRO detect or compensate for these errors which are at least 0.001" and therefore 5 x the 0.0002" accuracy of a DRO but will not be indicated by the DRO?

Being a "machinist" is not all about feed rates, speed, "hogging" or using a DRO. Anyone can do that. A good machinist "knows" his machines as well as their limitation and capabilities and as well as how to use or counter them to get the job right as specified.

A good job on a machine is not always how good the machine is but it is all about how good the machinist is.

A good DRO is a real help but it must be used as a tool and not as a crutch.

There is no excuse for mis-reading a tool. There is no use in griping and moaning about "numbers of decimal points" on a DRO or a job or a drawing.

The moment you take the job on you are assuring some-one - yourself included - that you are up to the job.

And if you can't do it?

oldtiffie
02-08-2010, 02:13 AM
How do you know if you've hit say 4.0005- could be 4.0027 for all you know, or 3.9968. I just found not long ago that my digital caliper is out by enough that it makes reading or working to tenths a wasted effort.

It might be that for most of us, it's seldom important to get the overall length of a part exactly right within a thou or less, but it would be more important to be able to fit a bushing properly, or create the right geometry to ensure a press fit for a stud for example. Most often that's going to mean working to something closer than a thou, and probably of even more importance- knowing how to interpret an inside and outside reading with any particular caliper or measuring instrument. You might carefully machine a shaft to 1.0005, only to find that the bore that it's supposed to fit in (that you also machined carefully to size, say 1.0000, is actually 1.0017.

Are you working to tenths as read on your gauge when you're fitting something? Or do you put the gauge away and rely on a different method of ensuring that half-thou interference fit, or that half-thou running clearance for the cam on your model engine-

I work to tenths quite often, but usually only where it matters. Most of my work would not win any beauty contest- lots of your guys work would. When I do machine something to a close tolerance where it isn't needed, I consider that practice, and I try to gauge (sic) how much faster I can do that now than I could before. If it's time consuming, and it isn't needed, I don't do it. If it's not time consuming, and it's a matter of twisting that handcrank to be right on the mark, or being happy just to see that it's close- why not hit the mark.

By the way, in the last hour I've managed to turn out two of those precision washers for my washing machine cover- :) Hey, John- you in a hurry for those washers for your bolts?

Darryl.

You are asking or expecting somewhere between a lot and the impossible of your digital caliper.

Check the specifications here of a pretty good pair of digital calipers as regards accuracy and repeatability:
http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/Digital_caliper4.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/Digital_caliper5.jpg

http://i200.photobucket.com/albums/aa294/oldtiffie/measuring/Digital_caliper2-1.jpg

Circlip
02-08-2010, 07:02 AM
Shame on you John, quoting BS when it should have been ISO.

Always found it rather sad to have to obtain certification to state that you'd made the bits from the material requested to the drawing supplied thus proving that if it didn't fit properly it was down to the dipstick that designed it in the first place.:rolleyes:

Regards Ian

Hmmm, wonder what category accelerators and brakes fall into???

JMS6449
02-08-2010, 07:16 AM
The difference between the professional and home machinist - professional works to the needed accuracy (typically .001) while the home machinist grasps for tenths, but has no idea which .0001.

When working in .0001 or microns, it's by grinding, temperature control and gauges, not with a calpier to .0001

Oldtiffie hit the nail on the head with his (2) posts.

Ken_Shea
02-08-2010, 08:07 AM
The difference between the professional and home machinist - professional works to the needed accuracy (typically .001) while the home machinist grasps for tenths, but has no idea which .0001.

haha, that's kinda funny but also just BS, I think we've all had our experiences with the so called, self called "professional" what ever". There are HSM right on this forum that would put to shame many a "professional", and often it would not be all that difficult.