Bending plate steel without a big brake

I built up a gas tank skid plate yesterday for the Commando project and needed to make some long 90 degree bends. My dad's sheet metal brake was too wimpy to bend 1/8 inch so I put a rosebud on the torch and tried to heat and bend it with the torch and some angle iron. However there was no way to keep a long section hot enough to bend and the first bend came out pathetic. So I came up with what I call "bending on the dotted line". I marked the line I wanted to bend then clamped a piece of angle iron near the line then busted out the plasma cutter. Instead of cutting the whole length of the plate I alternated a pattern of cut for an inch skip an inch cut a inch , skip an inch. When I was done it was easy to bend it. Then I welded up the cuts and sanded them off. Maybe some of you already new this trick but it worked great for me.

 

[STAG]

Yup I learned that a bunch of people do it on their CNC plasma table too when making complicated multi-plane parts from one piece of material.

 

[Karnage Fab]

how long was the plate?
ive got a big sheet metal brake that has bent a 32" long piece of 1/8 with three guys on the break, came out clean too.
i bent up this bumper from 1/8"

 

[DaveB]

how long was the plate?
ive got a big sheet metal brake that has bent a 32" long piece of 1/8 with three guys on the break, came out clean too.
i bent up this bumper from 1/8"

Looks good, The pieces I was working with were as wide as 34 inches but the bends were around 24 inches.

 

[STAG]

Oooh that does look good! Great work Karnage.

 

[iamsparticus]

i have used a simliar technique to bend 3/16 plate for plate bumpers and the like. One piece i bent was 5 feet long! So first a clapped down the plate on the welding table with the the edge of the tabel just behinde where the plate needs to bend. Then i use a straight edge and draw my line. Using a angle grinder i cut along the line about 2/3 the way through the plate, you can use a angle iron for a guide but i didnt. Then make two cuts all the way through evenly spaced toward the middle. slap a angle finder on the piece to be bent then slowly put pressure on it till it bends to the desired angle. once at eh desired angle put a few tacks to stiffen it up and then weld up the gap and grind it smooth. You need to be careful that you grind only iin one direction when smoothing or it will not look uniform

 

[Spork]

Interesting thread, I've been debating what to do for a bumper and have access to a large press just need to figure out the long lines and how to keep them aligned.

So question how thick do you actually need for a bumper? I see lots of threads where people use 1/4" and 3/16" plate but that seems like overkill when my stock bumper is plastic with some metal backing. The frame rails on most vehicles aren't anywhere close to 3/16" so instead of tweaking a bumper in an accident you're bending frame.

 

[STAG]

Depends on how you're gonna beat it up, if you think you're only going to tap it everynow and then I'd go with 1/8", if you're gonna not be gentle with it I'd do 3/16", if you're going to really show it who is boss I could see 1/4". And I wouldn't worry about the frame, your bumper tie-ins should be designed to spread out the load well enough to be a non issue. Also, any winch mount plates I'd do in a minimum of 3/8 for rigs under 3.5k lbs, 1/2" for rigs 3.5k+.

However that's all only what I'd be comfortable with, those numbers have no calculation

 

[iamsparticus]

we have built all our plate bumpers out of 3/16's if you structure the bumper right and reforce any open areas it will take all the abuse you can dish out