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What are the actual tolerances for a "Min" or "Max" dimension callout?

Finegrain

Diamond
Joined
Sep 6, 2007
Location
Seattle, Washington
I am working on this part, which has the following tolerance callouts:

Min Max tolerances.png

The blanket 1-decimal tolerance is +/-0.25mm and the 2-decimal tolerance is +/-.08mm. So, is the 22.6MAX supposed to be 22.6 +0/-.25, and the 12.53MIN supposed to 12.53 +.08/-0? Or could the space between the ears be, for example, 12.7mm? It's not really a problem for making this particular part, I can hold everything within the .25mm and .08mm, I'm just curious.

Thanks, and regards.

Mike
 

sfriedberg

Diamond
Joined
Oct 14, 2010
Location
Oregon, USA
There are three plausible interpretations, and there's probably a clause in some ASME/ISO spec somewhere that says which one is correct. When in doubt, ask the customer.
1) 22.6 +0 -anything consistent with other dimensions
2) 22.6 +0 -0.25 This is half the title block tolerance range
3) 22.6 +0 -0.50 This is the title block tolerance range, just stated at the high end of the range
My inclination would be to use the 3rd interpretation. But when in doubt, ask the customer.
 

BoxcarPete

Stainless
Joined
Nov 30, 2018
Location
Michigan, USA
There's theoretically no limit applied to those dimensions other than the fact that they have to be kept consistent with the others. In this case, it effectively turns your 5.04s into unilateral tolerances because 12.53 + 5.04 + 5.04 = 22.61 which means if you made everything perfectly to nominal you'd actually be over length.

On this drawing it ends up being constrained reasonably but misuse if MIN/MAX is a big pet peeve of my brother who is the go-to GD&T guy at his company. Once he asked an engineer who put 9.00mm MAX on a drawing if he drilled a 6mm hole would it be OK? No? Then put a frakkin tolerance on it!
 

guythatbrews

Cast Iron
Joined
Dec 14, 2017
Location
MO, USA
as long as the (2) 5.04 dims are in tolerance, there is no min on the 22.6 and there is no max on the 12.53
This says it all. If you make the part this way it will be to the print. Min means minimum max means maximum. No further thinkin' required.

Well don't really says it all. What a dumb way to dimension this. I guess maybe the designer thought he was making things easier for manufacture but he really wasn't.

I often see min/max dimensions misused. It is frustrating to have to go to the customer and explain the case.
 

Larry Dickman

Titanium
Joined
Jan 30, 2014
Location
Temecula, Ca
What a dumb way to dimension this. I guess maybe the designer thought he was making things easier for manufacture but he really wasn't.
I see this a lot on castings. I don't know if this is a casting or not, but lets say it is and the 22.6 ears are 22.4 out of the box. Then they wouldn't require machining
 

guythatbrews

Cast Iron
Joined
Dec 14, 2017
Location
MO, USA
I see this a lot on castings. I don't know if this is a casting or not, but lets say it is and the 22.6 ears are 22.4 out of the box. Then they wouldn't require machining
I suppose you have a point. But not likely with the +-.08 tolerance on the 5.04 dimension and the way things stack up it's too close for a casting. Maybe it would work for a die casting. Outside of my experience.
 

sfriedberg

Diamond
Joined
Oct 14, 2010
Location
Oregon, USA
If we take 5.04 to the low end of the title block tolerances and respect 12.53MIN as its low end, we get 4.96 + 12.53 + 4.96 = 22.45. We can "put back" 0.15 distributed across the three widths and still respect 22.6MAX as its high end. It might all go in one of the 5.04 nominal tabs, be evenly distributed, whatever. But one or both of the 5.04 nominals will have to be made under the nominal dimension to satisfy all the constraints.
If this drawing had been converted from dimensions with asymmetric tolerances (engineer friendly) to one with different nominal dimensions with symmetric tolerances (shop floor friendly), exactly one of the (converted) 12.53 or 22.6 should carry a REF notation, meaning that's just a convenient sum and that governing dimensions are the other ones.
 








 
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