Straightness tolerance on a piece of sheetmetal 1

[BraunP]

Hello everyone,

I am still leaning GT&D. Can you look at my print for the straightness tolerance. I need this piece to be straight. As of right now I have the tolerance set on both sides of the piece, but I have a feeling I cant put a tolerance on a datum. Help please. Thank you for your help.

 

[3DDave]

Money can be best saved if the standard is useable by people who can pick it up, read it through in a short time, and understand what it meant. The 2009 version, and the 1994 to a lesser extent, fails that criterion. Part of that failure is rooted in a reluctance to exactly mention the spec in question. Why GD&T instead of Y14.5? How can one be an expert at Geometric Dimensioning and have the basis document have no definition for the term? The practice is sloppy and I think it shows in the 2009 spec.

tl;dr Why not use the correct terminology instead of using something unrelated?

 

[MikeHalloran]

Punching that big central hole is always going to distort that part.

So add hand labor to hammer it flat, or
buy it laser-cut, or
buy it waterjet cut and
add hand labor to wash off the grit, or
planish the part (see the pattern on old relay frames), or
add flanges or corrugations.

As a general rule, if you want a sheet metal part to be straight, you have to hit it with a press brake at least once.




Mike Halloran
Pembroke Pines, FL, USA

 

[Gilmiril]

BraunP, I agree with the others that recommend using flatness rather than straightness.

Conceptually, straightness and flatness are the same principle except that the former applies in 1 dimension (linear) and the latter applies in 2 dimensions (planar) rather than just 1 dimension (linear). Also note that flatness applies in the direction of the view on which it's applied, so in your original drawing, it applies to individual line elements in the vertical direction only (and thus does not control straightness in the horizontal direction). Flatness would control the entire surface, which is what it sounds like you really do need.

 

[SDETERS]

With the rollover from the stamping process does this have to meet the flatness, if you apply flatness to the part? Maybe you want your part flat in only a certain locations. Due to the fact from the stamping process you will have burrs and rollover.

 

[BraunP]

The entire part needs to be flat. not just on a particular area. Its in one area (where the hole is) that you can see the bend.