I'm looking to put a 90 degree bend in a 18" to 20" wide piece of 16 - 18 ga sheet metal. I've read a little bit online about using angle iron and 2x4's. Does anyone have experience doing this without a sheet metal break?

Someone at the last meeting said that George Dixon's book had something on this, but I have not found it.

Thanks in advance!
Jim

That is a pretty good design and clear presentation. I'd looked at a number of things on the internet,but had not run across that particular one. Thanks!

Thanks for all the tips in the forum and sent to be personally. I've completed the project that prompted this question and wanted to share the results.

Project description:
I'm building a 'super sucker' side-draft chimney based on the design on anvilfire. (Okay, I finally got tired of too much smoke in the shop at times!).

How I bent the metal:
The key tips that helped me are: (1)simply using two pieces of angle iron clamped together and making multiple passes with a hammer to bend the metal. (from Dan Tull) (2) fullering a crease along the line before bending (a George Dixon technique shared by John Myers). The first tip really simplified my tooling and helped quite a bit. The second tip made the process much easier and precise.

Here's a picture of hammering the crease. I'm using basically a rounded fuller for leaf veining to make the crease (you need to avoid using something sharp, like a chisel. Otherwise you risk creating a fracture).



Next you clamp the sheet metal down between two hefty pieces of angle iron:


Ensure the crease is down and aligned with the edge of the angle iron:


Then you apply slight down pressure on the free end of the metal, and lightly hammer across the sheet where you want to bend it:


Keep making passes until you reach 90 deg.:



I made a couple of extra passes to clean up the bend and give it a more professional look:



Here's the super sucker just about finished. If you made it to the Sept 09 meeting you would see it complete and painted on the 'show and tell' table: