Allowences And Tolerances

[Swerdk]

Looking at machinist handbook and trying to understand how to read a number that they say is in thousandths

See pic

Example : -0.2 is what? A lateral tolerance of 2 thousanths of an inch? I thought it has to say -.002 to be two thousandths Pick any number from the pic and let me

 

[coffmajt]

Just below the classes of fits the chart says "All values in thousands of an inch", so I would take .25 to mean one quarter of one thousandth of an inch -- The numbers seem consistent with fits I am familiar with == Jack

 

[JimDawson]

Just below the classes of fits the chart says "All values in thousands of an inch", so I would take .25 to mean one quarter of one thousandth of an inch -- The numbers seem consistent with fits I am familiar with == Jack

:+1:

 

[dave2176]

Just below the classes of fits the chart says "All values in thousands of an inch", so I would take .25 to mean one quarter of one thousandth of an inch -- The numbers seem consistent with fits I am familiar with == Jack

Agreed. So when you see -0.2 it is -0.0002 or minus two tenths rather than saying minus two ten thousandths. 0.020 is expressed as twenty thousandths rather than two hundredths even though the later is mathmatically correct as well. Hundredths is used when describing 0.00002 as two hundredths rather than two one hundred thousandths. Don't know who came up with it but I like it. Mmmm, I wonder how you would say 0.000002.
Dave

 

[Tony Wells]

0.000,002,(0<--implied) would be called 20 millionths.

 

[Swerdk]

Why .0002 and not .002 if the book states its in thousandths


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[Swerdk]

Ugh!!!


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[Tony Wells]

Well, if it says 2 (whole number) it would be 0.002 (2/1000), but they slide a decimal point in there to make it 2/10000

 

[Swerdk]

I get what you guys are saying but you do realize logically this makes no sense


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[Tony Wells]

I'll grant that the method of expressing the dimensions in the fit chart is a little awkward. It does not follow normal machining "lingo", but the information is clearly expressed and accurate. I've been at this a while, and to me it makes perfect sense. However, if I needed to use this type of information on a regular basis, or had employees who used it, I would probably "translate" this chart into something more people are accustomed to seeing.