Tolerance Chains & Tolerance Stack-up
Tolerance Chains & Tolerance Stack-up
(OP)
Does anyone know where I can find information on Tolerance Chains, Tolerance Stack-up, etc. I've searched the web and found very little.
I'd love to find a website link but any information whatsoever is greatley appreciated.
Thank You very much and Merry Christmas!
I'd love to find a website link but any information whatsoever is greatley appreciated.
Thank You very much and Merry Christmas!





RE: Tolerance Chains & Tolerance Stack-up
RE: Tolerance Chains & Tolerance Stack-up
Unless you know Russian, I do not know any book and website related to the topic.
Viktor
http://viktorastakhov.tripod.com
RE: Tolerance Chains & Tolerance Stack-up
RE: Tolerance Chains & Tolerance Stack-up
RE: Tolerance Chains & Tolerance Stack-up
I have found, though, that many engineers and designers can not do this simple arithmatic. Someone who can do 3rd grade math is portraid as the department guru.
All tolerance analysis needs is time, a trusty calculator, and a focus on what the final (functional) design requirements are.
As zzy stated above, there are computer programs that do tolerance stack-up, but for the most part this technology in relation to CAD is in its infancy and rather cumbersome to use. You are better of doing it long hand.
If you have a specific example that can be described here, I'd be happy to walk you through one.
--Scott
RE: Tolerance Chains & Tolerance Stack-up
I appreciate your input.
I would love to send you a copy of the assembly I am required to do a tolerance Analysis on but I am not permitted to do so -- my company has confidentiality concerns.
However, I can attempt to explain my situation a little. I am a designer for a German owned company located here in the states. We are nearing the completion of a major electro-mechanical project; however, a lot of Assembly interface problems have cropped up. As a result, we are now required to do Tolerance studies on all our Assemblies. I have only worked here a couple of years and I was not part of the original development team. I am told that some sorts of Tolerance studies were done in the past but not in a method that would satisfy the German owners. Our German friends seem to be more adept at these Tolerance Stack-ups than we are.
We have very small and intricate parts that make up some of these assemblies. Some of the assemblies have parts with multiple interface points and some of the parts rotate as well I would like to find any info on how to do these Stack-ups correctly. Do you know if there are any standards, and/or rules governing these Tolerance Stack-ups? If I had something to use as reference or some examples to go by then maybe I could see exacly how to do these; anything would be helpful and welcome.
Thanks again.
RE: Tolerance Chains & Tolerance Stack-up
Cheers
RE: Tolerance Chains & Tolerance Stack-up
Even for a simple calculations one should know about tolerance fields, basic dimensions, nominal size, MMC, unilateral and bilateral tolerances etc. Moreover, one should be well aware about a number of statistical distributions occurred in manufacturing. On the top of that, it is desirable to know the assembly and working temperatures of the unit, properties of materials of parts included into calculations.
When one wants to do it for real, he/she should complete the analysis by the optimization of tolerances accounting for many real-life factors. The result is truly amazing and rewarding for those who know what this analysis and optimization is all about.
Viktor
http://viktorastakhov.tripod.com
RE: Tolerance Chains & Tolerance Stack-up
RE: Tolerance Chains & Tolerance Stack-up
http://www.uts.com/products/ssdoc.html
Looks like a nice toy.
Viktor
http://viktorastakhov.tripod.com
RE: Tolerance Chains & Tolerance Stack-up
Nasty questions you need to ask to do it properly: is each tolerance normally distributed? are any tolernaces cross-coupled during the manufacturing process? what is/are my measure/s that define a good assembly?
A good example of tolerance control is the BMW X5s engine/gearbox/transfer case/diff assembly.
The driveshaft needs to be in line with the output gear of the transfer case, and the pinion nose of the diff. The diff is bolted to the sump which is bolted to the block which is bolted to the bellhousing which is bolted to the transmission which is bolted to the transfer case. How do you maintain angular and positional alignment across all those interfaces? I wouldn't mind betting the maximum permissible angular error is a couple of degrees, and maybe 2 mm in positional error as well.
Cheers
Greg Locock
RE: Tolerance Chains & Tolerance Stack-up
Viktor
http://viktorastakhov.tripod.com
RE: Tolerance Chains & Tolerance Stack-up
RE: Tolerance Chains & Tolerance Stack-up
VSA, currently from EDS.
Valisys, which was developed at the same time as VSA, but is separate.
Technomatix comes to mind as the supplier.)
3DCS from Dimensional Control Systems
CE-TOL from Sigmetrix (via ADCATS) (Pro/Engineer only)
The trouble with 'hand' calcs is that without a lot of practice and some accurate feedback, the analyst can convince himself of most anything. This is especially true when dealing with datum reference frames. Just as few people can write a computer program that runs right the first time, few people really understand the results that will be allowed for all but the most trivial dimensioning schemes. What they -think- will happen is what is analyzed, but not what is -allowed- to happen by the drawing requirements.
VSA was not a trivial program to use, but the interface has likely improved. It was more lifelike than CE-TOL (formerly TI-TOL) seemed to be, though arguments can be made on either side for particular facets of dimensional and tolerance. investigation. If I had only one? VSA.
RE: Tolerance Chains & Tolerance Stack-up
As for tolerance chains, assuming you are referring to chain dimensioning with bilateral tolerancing, the problem is completely eliminated with the use of positional tolerancing per Y14.5M.
As others have indicated, a full tolerance analysis, even with a computer program, can be quite involved and expensive.
Bruce
RE: Tolerance Chains & Tolerance Stack-up
VSA from EDS was used. They sent their own people in. I recommend it highly.
Merry Christmas & Happy New Year.
fastech
csft, inc.
Bill P.
CSFT, Inc.
RE: Tolerance Chains & Tolerance Stack-up
If there is only one assembly which needs to be evaluated, a good spreadsheet and a thorough knowledge of what you calculate are sufficient.
The second part - the knowledge - is the most important. It is always necessary, also when working with any commercial software.
Merry Christmas !
gearguru
RE: Tolerance Chains & Tolerance Stack-up
chains should be responsible enough to provide
what appears to be a simple problem at least
to the tolerance ranges. As to stack up of
tolerances, I would assume that you would be
interested only on how is affects the sprockets
and not what is happening on the free chain.
The chain manufacturer must also know the tolerances
that allowed on the the sprocket for this to
work. I would work with them as they have more
knowledge about their product than others.
RE: Tolerance Chains & Tolerance Stack-up
I aplogize for not being more specific. In my original question ("where I can find information on Tolerance Chains, Tolerance Stack-up, etc.."), when I refered to Tolerance Chains, I meant "Dimensional Chains" -- not "Chains" in the literal sense. Sorry for the confusion.
Thanks for your input,
Steedj
RE: Tolerance Chains & Tolerance Stack-up
Thank you so much!
All of you have provided me with both helpful-information and interesting-insight into Tolerance Stack-ups. I know much more now than I did prior to posting my question.
Thank You very much and Merry Christmas!
RE: Tolerance Chains & Tolerance Stack-up
Viktor,
You mentioned optimisation (appropriate only for large run manufacture), how would you realistically go about this? From my own knowledge its is only possible to do this if an accurate mathematical model of the system is available, or a large number of costly experiments are run. Then of course you would have to decide what you wish to optimise, this would not be not be straightforward if you are simply trying to ensure your assembly fits together.
Thanks in advance
Damien
RE: Tolerance Chains & Tolerance Stack-up
As known, any solution of the reverse problem is not unique. The word “optimization” means the solution which meets the assigned criterion of optimization. It could be the minimum cost criterion, the best fit criterion, the same class of tolerance of each component, etc.
Viktor
http://viktorastakhov.tripod.com
RE: Tolerance Chains & Tolerance Stack-up
RE: Tolerance Chains & Tolerance Stack-up
tolerance stack up and much of it depends on
what is critical and how the parts go together.
I always use bilateral tolerances and sometimes
it is a rough call to determine which datums
are necessary to dimension from. Only the
designer can make these decisions or consult
with a good detailer and shop man.