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position tolerance

position tolerance

position tolerance

(OP)
can a feature's position tolerance having itself as a datum?
i like to control the hole location real tight ref to main axis and end plane, but it could be loose relative to flange orientation.
if the part axis A, end surface B, the hole in concern C, the position tol of the hole "POS dia .002 S A B C".
or i must generate the line connecting two flange holes as D, then specify "POS dia .002 S A B D"?
thanks.

RE: position tolerance

dho,

That makes no sense. If a feature is tagged as datum A, its location to datum A is perfect, by definition. Also, please do not say "axis". You cannot apply a datum to an axis.

You can specify datum A as the end face, and datum&bnsp;B as your critical diameter. On that diameter, a positional tolerance will have no meaning, but perpendicularity to A is perfectly reasonable. I would not call up a diameter as a primary datum unless it was long enough to accurately define an axis. By specifying a face and diameter in that order, you specify a face for perpendicularity, and a locating feature.

--
JHG

RE: position tolerance

Question to dho: Exactly which of the holes shown on the picture is your hole C? Which features are datum features A and B?

Question to drawoh: Can we really specify the end face and the critical diameter (whatever it is in this case) as datums A and B respectively, or rather as datum features A and B?

RE: position tolerance

(OP)

RE: position tolerance

Are we really sure it is functioning like shown, or maybe the face parallel with the shown datum feature B should be the primary datum feature?
Then A should be secondary and everything else should be positioned / profiled to B primary and A secondary.
No need for clocking. And the simultaneous requirement will take care of the clocking.
If the part is measured on the CMM and the clocking is needed, then the inspector is free to pick any of the flange holes, but will make the inspection more stringent than the designer wants/allow, in other words will reject some good parts due to an artificial alignment imposed by the CMM and not by the function.

RE: position tolerance

(OP)
A as primary, so, the .312 hole intersects the main bore.
if B as primary, only keep the location from B right on.

RE: position tolerance

Could you tell us how this part you are trying so hard to define interacts with its mating parts? How fit in the assembly?
What would be the physical reality of this assembly?

RE: position tolerance

(OP)
just envision a ball valve.
even a loose fit assembly, i think it still needs proper GEO tol callout.
as CMM measurement wise, the machine can setup A first, B second and finally line up C.
thanks.

RE: position tolerance

dho,
I guess you did not answer my question, did you?
"Could you tell us how this part you are trying so hard to define interacts with its mating parts? How fit in the assembly?
What would be the physical reality of this assembly?
"


even a loose fit assembly, i think it still needs proper GEO tol callout.

I agree!!

RE: position tolerance

(OP)
i answered. if you envision a ball valve.
thanks,

RE: position tolerance

Okay.

The follow up question: do you need help or you are trying to make sure everybody on this form will have some imagination of the product you are designing?

RE: position tolerance

(OP)
i just have a different opinion as you have.
here i was asking (for help) to properly specify a position tolerance. whatever this part is used in a ball valve, or anything, precise or coarse, does NOT matter.

RE: position tolerance

I agree. But what DOES matter is how the product FUNCTIONS.

RE: position tolerance

(OP)
that will be the design issue. a good product or bad.
it has NOTHING to do with correct way of GEO tol.
thanks.

RE: position tolerance

If you think the product function has nothing to do with proper geometric tolerance of location, then you need more help than you realize.

It is very difficult to suggest the best solutions without knowing the part well enough. You have called out obviously incorrect or inferior constraints, but in order to suggest something better, more information is required, as asked.

RE: position tolerance

Wowww! I learn something new:

"the design issue. a good product or bad.
it has NOTHING to do with correct way of GEO tol."

The design has nothing to do with the correct way of GEO tol.

The question is: then WHO has ? (to do with the correct way of Geo tol). Manufacturing? Purchasing? Quality?

RE: position tolerance

THANK YOU JNieman !!

RE: position tolerance

(OP)
you have to read the whole threads. not jump into conclusion.
does anyone here know how to proper GEO the .312 holes which intersect the c.l. of 1.147 bore and XX distance away from B?
have a good day.

RE: position tolerance

dho,
What standard are you using to define the print?

RE: position tolerance

(OP)
ASME Y14.5.
i still would like to ask. would anyone specify the GEO tol for this part properly. so, it has a tight control on the .312 hole intersecting the main bore at 90 degrees and away from the end surface XX distance, but could be off some relative to flange orientation?

RE: position tolerance

See 7-41 from 2009. Use same concept, but add flange/holes location to the same DRF.

RE: position tolerance

(OP)
so, my 3/31/16, 19:46 thread, geo tol in red "circle" would be acceptable.
thanks.

RE: position tolerance

Drop D as tertiary from upper segment.
Drop the second segment
Add 2x pos. req. for the flange holes to A primary and B secondary.
Add profile req. for the flange shape/size to A primary and B secondary.

RE: position tolerance

dho,

When we ask about part function, what we mean is how does this part interface with the rest of it's related components. I see a flange with holes in it. This highly suggests that the flange bolts against something. If this is true then the flange face would probably serve as a better---and more functional--primary datum feature.

I just can't help but bring back up your notion that proper GD&T has nothing to do with function. It has everything to do with function, that's why we're asking questions before just throwing out random suggestions. This part can be properly toleranced in a variety of different ways but the one that communicates function is the one to use.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

RE: position tolerance

(OP)
i know NOT much in geo tol. but i think geo tol is a tool to explain the designer's requirement in a universal way so everyone interpret it the same.
so, in this thread, the question is how to geo tol the part so the .312 hole is intersect the main bore in 90 degrees (most important), and at a specified distance from front end surface A, (second important). and lastly, line up with the flange. (it is well asked in my initial posting.)
just as ASME Y14.5 (2009) fig 7.41, it tells the proper way to geo tol, a redial hole WITHOUT discussion how this part is designed if proper for its function.
i know NOT much geo tol, i say it again. so, i am looking for help/guidance.
thanks to everyone who answered my call.

RE: position tolerance

dho,

This is futile. You acknowledge that you don't know GD&T yet you argue that it isn't necessary to know part function in order to properly implement it.

Good luck getting anyone else to help. You've argued your way out of any real help thus far.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

RE: position tolerance

(OP)
i would allow different opinions. i would categorize this as discussion. if it is some sort argument, what is wrong to argue about a tech issue?
the end of this thread.

RE: position tolerance

The problem is that you're arguing about something that you admittedly know nothing about.
Now you can end the thread.

John Acosta, GDTP Senior Level
Manufacturing Engineering Tech

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