Tolerancing Dispute 1

[MaddMaxx]

Can someone help me resolve an issue. When I use limits tolerancing, where it shows both an upper and lower dimension that a part can be made to, I'm used to showing the upper dimension above the lower. I'm now told that is incorrect and it should be reversed, showing the lower on top.

Is there an actual standard for this or is it just a matter of preference?

Thanks in advance

 

[GDTGUY]

ASME Y14.5M-1994, paragraph 2.2 (a) states the following for limit dimensions:

"(a) Limit Dimensioning. The high limit (maximum value) is placed above the low limit (minimum value). When expressed in a single line, the low limit precedes the high limit and a dash separates the two values.”


Hope this helps.

GDTGUY

 

[MaddMaxx]

Thank you very much. That's what I thought but was not sure.

 

[TheTick]

I know it's against the standard, but I tend to deviate from that. I go with "maximum material condition" (in the same vein as GDT). If it's a hole, I put the small value first, so it can be enlarged if needed. If it's a "positive" feature like stock length, I put the high value first, as it would be reached first when removing material.

If the ladies don't find you handsome, they should at least find you handy.

 

[Mandrake22]

Prior to reading GTDGUY's post I did it the same way as TheTick and I even used the same logic. I didn't know there was a standard.(too lazy to look I guess, even though I have a shortcut to the ANSI standard on my desktop!) It seemed easiest to just remember "MMC". This method also seems to require somewhat less mental gymnastics when trying to figure the fit of a shaft in a bore for example. I know it sometimes makes for extra effort with Solidworks to force the software to display the limit dimension as I want it to. I passed a decree on Wednesday that everyone was to follow the ANSI standard from now on! Looks like I will have to flip a coin now.

 

[ctopher]

We always follow the standards. Too bad not everyone does...I wish they did, I wouldn't get so many calls from vendors who do not understand the dwgs.

 

[11echo]

This is like when you mirror welding symbols, everybody knows what you mean, BUT it's a big pointing finger that the author doesn't fully know what they are doing! This may sting a bit to those of you that "do their own thing", BUT it's plain POOR PRACTICE! ...And if you work for me, you are called on it. ...Mark Layport (Design/Drafting Supervisor)

 

[CWIC]

I'm sure just a typo, but isn't that ANSI Y14.5 GDTGUY?

 

[looslib]

NO. The 1994 spec is officially listed as ASME, not ANSI.

http://members.asme.org/catalog/ItemView.cfm?ItemNumber=N00594

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli
CAD/CAM System Analyst
Ingersoll-Rand

 

[CWIC]

Thanks for the heads up! I guess my old ANSI copy is obsolete.

 

[dave048]

Perhaps the misunderstanding about which dim to put on top persists because the standard has changed. The older standard (I don't remember the version# but it was some time ago) used to specify that for ID dims the smaller number goes on top and the larger on bottom. Now, the larger number is always on top.

 

[CadAndy]

I have to say it depends on your boss.

My Boss has to have everything the old
way. As he says the people in the shop
can bearly understand english and he
doesn't want to change anything.

Its hard because you get trained under
the new ANSI standards and some of the
Engineering Managers don't like it so
they don't use it. They continue to
use the old way to make things simple
for the people in the shop and themselves.

 

[procadman2]

Just to add 2 more cents...

Many high end software programs do not allow deviation from the ANSI/ASME standard of large dim on top.

Personally I do not like using "limits" Most machinists/programmers will shoot for the median dim. The true tolerance also is not always obvious. This requires someone to recalculate this figure allowing more room for error.

I prefer the "even plus/minus standard". The median is obvious as is the tolerance.

(This is just an opinion of 30+ years of engineering and machining.)

procadman2
Proe Design & Admin
NASA Contractor

"You can't build a reputation on something you haven't done."
H Ford

 

[automationbabe]

This is going a little off subject...while I believe ease of machining and programming is a plus that I consider, there are times where you just can't avoid the ther dimensioning stlyes.

One company I worked for wante the +/- tolerancing so much in manufacturing that all our dimensions were that way. The only way to maintain our design intent and tolerancing for some parts resulted in 5 digit numbers. Manufacturing had a cow...but it was what they asked for.

Sticking with topic...GDTGUY is correct in his statement per the standards.