What Do All Those Zeros Really Mean?

Bill C. said:
That is a shame they would do that to your finished drawings. Those machinist were blaming you for all errors. I had a few prints sent back the project designer for clarification. I have messed up some short run production parts because I misinterpreted a print.
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It's all good, they didn't know that I did the drawings. But I notice it when the questions came up and the NCR's started coming to my mailbox! I deal with several shops all over, including this one in China. The people over there are very helpful in dealing with problems like these. There are a couple of people over there that are very fluent in English, they are the one's I talk to through email.

I have a digital readout I mounted on my Sheldon lathe last year. Drives me nuts, it goes out to six places! I can't even count that far, much less get the movements to zero out to six places!
 
Cactus Farmer said:
I'm having some internal unease with some folks use of the 4th and 5th digit when talking about machining parts. Most folks can't measure to the 0.0000 with precision, and surely not to the 5th place. By including this place holder you are implying that you can actually measure that accurately . Most can't. I have a comparator and it measures to the 1/10,000 and I can infer to the one hundred thousandth. But I would be very cautious about writing it as such. Do they not understand that to 0.000 is pretty close to perfect. I have pin gauges in minus sizes and a few in the plus range. With a mike you are hard pressed to "see" a difference. The comparator will allow me to "see" it but only with the shop warmed up to a "standard" 70 plus or minus degrees. And then only it has had time to make the machine reach the same temp. The base of the comparator is BIG cast iron and warms very slowly. Is there a need for a lesson of accuracy? Most folks know "ain't" is not proper but "irregardless" is not too. Both are double negatives......Flammable and inflammable? Is one capable of burning and the other not? No, both will toast your behind if handled carelessly.
It just irks me no end for the language to be used poorly. I want to be accurate in my making of things but I want to convey what I did as concisely as possible with a common understanding as to
what I mean with a written explanation.
It seems like the most measurements that bug me are bore diameters of barrels. And sizes of the bullets that are fired through them.
To restate the idea, 0.10 implies accurate to 1/100 of an inch. 0.100 is accurate to 1/1000 of said inch , and 0.10000 is accurate to 1/10,000 if that inch. As I stated above, my comparator has a 2 1/2 inch thimble to to move the stage but it is still 0.025 per revolution just like a standard micrometer. That spreads the 1/1000 marks to about 1/2 inch apart. There are small marks between the 1/1000 marks that corespond to 1/10,000 if an inch. If I need a quick check on a tap for size and TPI it is not a big deal to measure the needed dimention. If "class of fit" for that same tap is required I need to wait for the shop to stablize temperature wise before attempting a measurement. Temperature makes things move!
So, adding zeros after the first three places is you impling have measured something with this degree of precision.
Most jobs require 0.001 accuracy or so. Putting that extra digit after the one thousants place is not adding precision if you can't measure it with sureity. If I need a tight fit on ,say, a bearing fit, -0.002 will surfice.
0.125 is an eight of an inch. Now measure 0.124 or 0.126 with that steel rule and tell me the difference. You are better than me if you can see that little change. The same applys to micrometers. 0.0011 and 0.0012 look a whole lot alike in your warm hand.
What I am trying to convey is adding a 4th digit may look cool as everything, your work will not be any better that your measurements.
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Danger: You have brought up some thing an early math teacher I had long ago would
carry on about . Do not report result more accurate than you sources.
 
I would see guys using files, emery paper and not realising a file gives you a bunch of diameters so one might be right, if you want accuracy on a lathe put a tool post grinder on it, that changes the game
 
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