Technique to round corner sheet metal

[Whiskeymike]

Can you guys describe techniques for rounding a sheet metal hem around another piece of sheet? Specifically the corners? I’ve searched a great deal, but I’m not getting the right keywords.

I’m trying to wrap the edge of a piece of sheet metal to protect the handler’s hands. For instance, I have a rectangle piece of sheet metal 18”x12” of 16-18ga steel with rounded corners. I’m hoping to take a 3/4” wide piece of sheet, form a hem of it folded in half and wrap that hem around the rectangle.

If it was not a hem, I would use a Shrinker/stretcher and wrap it around the corner. But doing it as a hem has me stumped.

 

[ez-duzit]

There are standard techniques used for hemming sheet metal. Scroll down to "double hem".
http://sheetmetal.me/tooling-terminology/sheet-metal-hems/

 

[matt_i]

I can think of two possibilities. One is to make your doubled piece and form it around the other part (I'd try hammer-forming it around a pipe for lack of other tools). Probably have to tack weld the hem to hold it together as its bent to keep the two thicknesses from wanting to separate due to the different bend radii, then tig weld & metal-finish the transition. Sort of like an inverted shallow baking-pan, correct?

The other would be to do it HVAC style and layout the rounded corners as a sort of "sunburst" with individual fingers that have to be bent over. Integrate the hem into both the flat and the fingers, those would also have to be welded and metal-finished at the end. Its probably less overall welding but the rounded corners won't be as smooth due to the segmenting.

 

[joe49]

Tuck shrink. If you used heat just bending the corner would create the tucks.

 

[dr_clyde]

The straight line hems are easy, just bend as far as you can with acute dies and then change to flattening dies with a spacer piece of metal in the middle.

The corner kind of depends on the radius. I would start with a straight hemmed piece, cut reliefs through the sides and pull it into the radius, then weld the cuts and blend. If the radius is super tight, that may not work well, and you'd have to make it out of multiple pieces as a weldment.

 

[whateg01]

Tuck shrink. If you used heat just bending the corner would create the tucks.

That's what I've done for that situation!

Dave

 

[matt_i]

How thick are we talking here?

 

[steel 35]

There are standard techniques used for hemming sheet metal. Scroll down to "double hem".
http://sheetmetal.me/tooling-terminology/sheet-metal-hems/

Did I read the tonnage on that correctly seams my Swag clone finger brake may just do that
(Brake that is)

 

[Whiskeymike]

It’s basically 16-18 ga. I may make the hem piece from 20-22ga. The project is making a storage box from an old Jerry can. Plan to cut a large door, attach it with a piano hinge, a couple latches on the other side. Because I’m cutting the door out of the can, I can’t make the hem in the door material. So I have to make it separate and then weld it in.

I’ll try the methods mentioned - heat, relief cuts, and a hammer. Thanks for the advice guys.