How much would be differenct between these two types of tolerating ?

[LCform]

Hi All

for a cylinder that is supposed to be inserted into another container(cylindrical) how much is it different if I put for its external diameter : 78 h7 (-0.03 ,0 ) or if I dimension it : 78 (-0.4 , -0.02) ?

 

[drawoh]

LCform,

Take a look at the ANSI limits and fits in your Machinery's Handbook. These are based on ISO tolerances. They classify and explain a huge series of fits.

--
JHG

 

[CheckerHater]

You forgot to tell us what tolerances you have on your "other cylinder"

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[Belanger]

Unless I'm missing something, here is the difference...
Using your first method, the limits of size would be 77.97 - 78.00
Using your second method, the limits of size would be 77.60 - 77.98

Seems like a pretty significant difference.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[LCform]

CORRECTION :

I apologize , the second tolerance was 78 (-0.04 , -0.02), I know the ANSI limits and fits like h7 and so , but sometimes the tolerances are chosen like arbitrary ? that I don't find it in the handbooks , that's why I asked

 

[CheckerHater]

Your tolerance is only half of the problem.

If your part is surrounded by nothing but thin air, it doesn't matter.

You have to think in terms of "fit".

So, once again, what is the tolerance on the mating part and what kind of relationship between the two you want to achieve?

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[SwinnyGG]

Checker has it right- the tolerances for an ISO fit aren't 'arbitrary'- they are based on a fit type and a size window. Pick your fit type, specify the code. Leave it to your machinist to look up the tolerance in the chart (i.e. your dimension should read <diameter symbol> 78 h7, NOT <diameter symbol> 78 h7 +0.00 -0.03)