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Inside Bend Radius Call Outs

Inside Bend Radius Call Outs

Inside Bend Radius Call Outs

Quick question for you all, on sheet-metal drawings where forming will occur if the inside bend radius is equal to the material thickness is a dimension or note required to specify this or is it implied? Thanks!

"Engineering is the art of modelling materials we do not wholly understand, into shapes we cannot precisely analyse so as to withstand forces we cannot properly assess, in such a way that the public has no reason to suspect the extent of our ignorance." - Dr. E. H. Brown

RE: Inside Bend Radius Call Outs

If not specified it is implied that you will accept any crap the vendor gives you.

Is that what you want?

RE: Inside Bend Radius Call Outs

haha, great point Mint.

However, is there a standard that out there that lists this as being required? I'd like to leverage the standard if I could to support this requirement where I'm at.

RE: Inside Bend Radius Call Outs


I doubt you will find such a standard. If you do, or if you write your own, I wouldn't be surprised if it occasionally gets missed by manufacturers.

Even if you establish that the nominal radius is equal to the nominal material thickness, you still probably need to provide a tolerance for the radius. This could certainly be done in the hypothetical standard, but it does add another layer of complexity.

Why not just add a drawing note with an appropriate tolerance such as "UNSPECIFIED INTERNAL BEND RADII SHALL BE R0.75+/-0.25"? This shouldn't be any more difficult than referencing a standard, and will probably be much more obvious to other drawing users. Additionally, it allows you to tailor the tolerance to the needs of each individual part.


RE: Inside Bend Radius Call Outs

There is no standard; there are minimum bend radii, which the supplier is not required to use. These vary with material, temper/heat treat condition, and thickness. I mention thickness because, for certain ranges, the minimums are specified as a ratio to the thickness. This saves having very complicated charts.

The main consideration is the supplier will have only a limited number of bending tools and can make only a few radii. So it is best to give as wide a range as possible or to call the supplier before releasing the drawing.

RE: Inside Bend Radius Call Outs

The bender needs to know what radius tool to use. Tell him.

RE: Inside Bend Radius Call Outs

Unless it will severely affect your part's function, leave it to the fabricator. Different materials show different resistance to bending with different results. See enclosed chart.

Don't tell manufacturer what tool to use (just like with tap drills).

If given no choice, provide radius with wide-open tolerance.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

RE: Inside Bend Radius Call Outs


You work out your bend radius based on your engineering principles. You apply the dimension to your drawing, with (generous) tolerances. Your fabricator follows your instructions. Your inspector can see what radii you want, and verify that they were done that way.


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