True position of floating part
True position of floating part
(OP)
Hi,
I have a dilema that I have not been able to resolve and am looking for some thoughts. I am dimensioning a design that hase a captured component that is allowed to float (retained movement) to help alignment during assembly of the next part. My customer is looking for a true position call out with variable data verification. I can't figure out how to dimension it. A standard true position will not show repeatability as the part moves by design within a range. If I dimension the extreme travel points with a true position it is relying on set up variations in cluding pressure (it is a plastic assembly). Any thoughts?
I have a dilema that I have not been able to resolve and am looking for some thoughts. I am dimensioning a design that hase a captured component that is allowed to float (retained movement) to help alignment during assembly of the next part. My customer is looking for a true position call out with variable data verification. I can't figure out how to dimension it. A standard true position will not show repeatability as the part moves by design within a range. If I dimension the extreme travel points with a true position it is relying on set up variations in cluding pressure (it is a plastic assembly). Any thoughts?





RE: True position of floating part
If the feature is round, then there is a diametrical tolerance zone allowance.
If the feature is not round, then I would suggest positional at MMC with the term "BOUNDARY" below the feature control frame. Now, it is the virtual condition boundary including orientation prevails over the centre of the feature. Unfortunately, this is best confirmed with a checking fixture.
Lastly, I hope that the Customer does not want capability studies on positional tolerances. It should not be performed since the results are a bit "bogus".
Hope this helps.
Dave D.
www.qmsi.ca
RE: True position of floating part
David
RE: True position of floating part
RE: True position of floating part
I presented a paper to an ASQ group during a dinner meeting and this subject came up. I have about 3 pages on this subject and would love to post them in a pdf file so one can read it with acrobat reader but I don't know how to do it here.
All the ones that I have seen are bogus and as long as you state that each hole or feature has a Ppk of 1.67, the Customer will love you.
Good luck on that one.
Dave D.
www.qmsi.ca
RE: True position of floating part
Have you tried to apply the formula in the standard for floating fasteners? If I understand your problem, that should provide a solution.
Thanks
Ringman
RE: True position of floating part
And yes 1.67 is my favorite number.
RE: True position of floating part
Hope this helps.
PS - the Ppk must be ABOVE 1.67 on samples and above 1.33 in the production run in automotive today.
Dave D.
www.qmsi.ca
RE: True position of floating part
Do I correctly understand that Positional tolerancing per ASME Y14.5 is being applied to the part drawing, but you dont know the formula for dimensioning? Houston we have a proble.
You need to get a copy of the stadard and study it.
ringman