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GDT - to control surface flat to concave (not convex)
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Posted by: coburnelli53

02/01/2007, 17:05:09

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I wish to know how to control a surface with GDT if possible. I need to assembly two parts together with a center fastener only - The second part is a polyvee belt tensioner, mounting to a larger flat stationary surface. The mounting surface of the tensioner needs to be flat, or up to .020" concave - convex will cause unacceptable contact area, and lead to failure from rocking due to variable belt loads and unloading.

What type of GDT (form control) would be used, and how would it be applied. Typically the toleraance is applied across the entire subject surface.

Would I need to use 'zones' that specify the outer portions of the surface separately from the center?

The 'footprint' of the tensioner surface is a diameter.








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Re: GDT - to control surface flat to concave (not convex)
Re: GDT - to control surface flat to concave (not convex) -- coburnelli53 Post Reply Top of thread Forum
Posted by: traingdt

02/01/2007, 19:20:29

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There are probably a couple ways to accomplish that. The easiest way is to simply use the flatness symbol to whatever amount you can allow, and then add a note below the feature control frame saying "concave only".
Some might recommend profile of a surface with a datum reference to that surface, because unlike flatness, it can be designated as unilateral. But that won't be any different in your case, because it still leaves open the question of concave vs. convex!
I suppose you could try to do something with zones (cross-hatched areas) but if the function of the part doesn't point to that idea, then I would avoid it.







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