use of an angle notcher/bender to make rectangular frame?

In short, do a test bend.

I would lay out a short piece of stock, carefully marking an inch on either side of the notch. Bend it on the notch mark, and then measure the one inch layout marks to each edge. I would recommend using a scribe for the best possible accuracy on at least the test bend.

That's the best way, but you can try to estimate the bend allowance as the difference between the length from the start of the bend to a straight corner and the length of the curved arc down the center (neutral axis) of the metal. Notice the bend allowance is LESS than the straight length of two mitered pieces.

Another way is to make a saw cut into the second leg to thin the bend line. This reduces the uncertainty of the bend allowance and makes it easy to form a sharper outside corner, but the inside weld is harder to clean up.

Jim Wilkins

You will be fairly close if you figure that the inside edge of the angle is the neutral axis. So if you want the outside to be 12" when using

1/8" stock, your notches should be 12" - 2x1/8" or 11-3/4" apart. That will get you close, do some test bends to see how much you need to adjust things.

You always have a problem with the bend work> If I have an angle notcher and bender, what is the exact procedure to

Since the metal will stretch in the bend, not compress, work by the inside dimensions only. You'll need to subtract 1/8" from one leg where the ends meet to account for the thickness of the angle, this will also give you a little wiggle room at the weld joint. Personally, I prefer to cope angle iron at 90 degree angles .

Shawn

IIRC, the machinery's handbook has a table of average bend allowances for a given material thickness. If it doesn't, a sheet metal reference book probably would. I usually do my sheet metal layouts in Autodesk Inventor, which does this automatically.

My rule of thumb is to take the thickness of the leg (1/8" in this case) and multiply it by 5. Subtract this from the overall length. Then on each end account for 1 leg thickness and 1 leg thickness on each bend. In other words for a 12X18" frame the lengths would be

11 3/4" 17 7/8" 11 7/8" 17 3/4"

The open corner takes up two of the thickness of the legs (for welding). Then each bent corner takes up 1 thickness. This will get you pretty close however it does make a difference how the bend is made so for extreme precision you'll need to do a test piece.