Straightness Tolerance concave vs convex?
Straightness Tolerance concave vs convex?
(OP)
I have a metal door, just a flat piece with formed edges for rigidity. The prototype had an issue with concave bowing. Concave bowing is not acceptable, but x-amount of convex bowing is ok...I'm not quite sure how to call this out on the drawing. I immediately think of a straightness tolerance, but that would allow both concave and convex bowing within the limitations. Is there a way to use straightness to allow bowing one way and not the other? Or can anyone suggest an alternative way of clarifying this on a drawing?
Thanks!
Thanks!





RE: Straightness Tolerance concave vs convex?
RE: Straightness Tolerance concave vs convex?
Having said that, my advice would be to associate an additional text note with the chosen form feature control frame explaining design intent as clear as possible.
RE: Straightness Tolerance concave vs convex?
As far as I can tell, OP was about “bowing”, not about reversals.
Not only bowing can be controlled by unilateral profile, but you can also apply “new” 2009 concept of “non-uniform” profile and simply draw the shape you are trying to control.
RE: Straightness Tolerance concave vs convex?
1. I was not thinking about reversals.
2. Even in your graphic (assuming I am reading it correctly), concavity will be possible. The surface will indeed have to lie above the true profile, but it still can contain concave areas inside this tolerance zone. But I agree that this option could be used - it at least assures that the surface won't fall below the true profile, so won't be concave in a classic way.
RE: Straightness Tolerance concave vs convex?
This is exactly what they call "reversal"
From my experience with sheet metal having your material bulging in one direction (even with some bumps) is an achievement by itself.
I am glad you agree that using "non-uniform" at least gives good idea of what one is trying to achieve.
RE: Straightness Tolerance concave vs convex?
RE: Straightness Tolerance concave vs convex?
So my question about applying the Y14.5-2009 ‘non-uniform’ unilateral profile callout is can I attach a note to or under the FCF to say “CONCAVE REVERSALS NOT PERMITTED” (or similar… suggestions?)?
PS: I hope my question compliments this thread and not creating a thread drift. If so I will start a new thread but it seems like its very in line with the OP.
lightweight, cheap, strong... pick 2
RE: Straightness Tolerance concave vs convex?
I think adding a note like that may not suffice.
There was a discussion about controlled radius not so long ago where some interesting comments about flats and reversals were raised, although the thread wasn't too long.
http://eng-tips.com/viewthread.cfm?qid=347084
The bottom line is, the note has to be very precise as to what the CONCAVE REVERSALS really mean to you.
RE: Straightness Tolerance concave vs convex?
lightweight, cheap, strong... pick 2
RE: Straightness Tolerance concave vs convex?
RE: Straightness Tolerance concave vs convex?
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