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Re: Need a GD&T question
Re: Need a GD&T question -- cmm227	Post Reply	Top of thread	Forum

Posted by: gm2612 ® 01/22/2006, 09:13:53 Author Profile eMail author Edit

Hey, even, you can ask your teacher, how to use GD&T for product performance optimization

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Re: Need a GD&T question
Re: Need a GD&T question -- cmm227	Post Reply	Top of thread	Forum

Posted by: tooleng ® 11/08/2005, 14:39:27 Author Profile eMail author Edit

Get your teacher to explain true position and how it effects tolerence stack. Usually if you ask three different people they will explain three different ways. Should be a good one to start. There are many questions that are more involved , but this one I find most interesting how people will explain w/out using a textbook.

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Re: Need a GD&T question
Re: Re: Need a GD&T question -- tooleng	Post Reply	Top of thread	Forum

Posted by: randykimball ® 01/22/2006, 10:20:01 Author Profile eMail author Edit

Ask how it applies to an actual manufacturing problem, the reason to study this kind of thing is to be able to apply it later. Here is an example: If we have a given transmission for, say a helicopter, and the top of the transmission gets a cover. This cover is 18" by 24". The transmission has 36 each of 5/16-24 bolt holes around the top rim surface in an uneven pattern to prevent misassembly. There are 4 each .250" dowels in odd places to assure alignment. In the center of the cover there is a bearing counter bore with a fit for a 40MM OD x 12MM thick bearing to fit flush with the top of the cover. This bearing must align with a shaft already installed into the transmission to a fit as to not add more than .001 to the existing TIR. Now tolerance the hole pattern so that if we send a cover to a repair shop working on an air ambulance the cover will fit their existing transmission correctly, lives will count on the fit... perhaps your own. I made this one up, but it is a clear example of what really needs to happen frequently, and is similar to a real case. The bolt holes are not allowed to be sized in the field because that would remove process coating which protects the magnesium case from electrolytic corrosion. All the dowell holes must fit close enough to effect the proper TIR of the bearing counter bore. ...... Now you know why a helicopter transmission cost $$$$$$$. The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them. Modified by randykimball at Sun, Jan 22, 2006, 10:35:00

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Re: Need a GD&T question
Re: Re: Need a GD&T question -- randykimball	Post Reply	Top of thread	Forum

Posted by: traingdt ® 01/23/2006, 12:03:00 Author Profile eMail author Edit

Here's another tricky question for GD&T folks. (Although it gets into statistics, so maybe it's better for stats or quality people): How can we do a capability study (i.e., statistically monitor a distribution pattern) for a geometric tolerance that has the MMC modifier? The MMC idea says that there may be bonus tolerance. So it's difficult to track a tolerance that itself may be variable! (The MMC idea implies that it's not a critical tolerance, so in the real world this issue should not arise often. But if you wanted to do it, I would say that we should actually track how the part matches up to the virtual condition, because that is the one thing that is constant.)

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