Dimensioning formed sheet metal

[smcadman]

I do not know if there is an ansi standard for this, but whenever dimensioning sheet metal formed to a closed 45 degrees (135), do you dimension it from one end of the flange to the theoretical apex, or from one end to the quadrant of the outside radius.
For example:
The below example is with .075 material thickness, and a flange dimension of 1.5 (outside radius being 2 x m.t.)

/ /
/ /
/ /
/ /_________
/___________

!---1.5 O.D.---!
Above is dimensioned to
"theoretical apex"

/ /
/ /
/ /
/ (_________
(___________

!---1.288 O.D.--!
Above dimensioned to quadrant of radius

We work with drawings from vendors who use both methods, but the problem is those on the shop floor have to use math to figure out what the theoretical apex is on drawings. If dimensioned like the second figure, they can just use calipers to check there parts without resorting to a calculator.
Are there any dimensioning conventions (besides company standards) that dictate what is the proper form of dimensioning this. This example is with 45 degrees, but we also get 55 degrees, etc.

(Hopefully the diagrams do not get too jumbled up to understand)

Flores

 

[drawoh]

smcadman,

My inclination would be to dimension to the theoretical apex. Your dimension to the quadrant of the radius is affected by the the bending point and by the radius itself.

You cannot do a direct measurement of the part with vernier calipers, but you can make a simple fixture, even out of cardboard, as long as your tolerances are not that tight. Even the drawing will work if it is at 1:1 scale, and your bend is close to a convenient edge.

Consider using an ANSI GD&T profile tolerance to specify the maximum run-out.

JHG