bending flat bar
Meant to post this a few days ago- anyway, I bent some flat bar for a project, using my home made bender. The brake bar and die are really made for bending sheet, but I've been able to bend 3/16 flat bar up to 2 inches wide in it. I'd like to be able to get tighter bends, which means the support points on the bottom need to be closer together, and in turn that means more force would be needed. What I now have in mind is to have a rectangular hole cut in some 1/2 inch plate, the hole being little more than the width of a hydraulic jack base in width, and only long enough to accommodate the jack, a bit of a base for the jack, and the die parts for the bending. The hole might be 5 or 6 inches wide, and probably twice that in height. It's very simple- the bottom die rides up and down on the jack post, guided by the sides of the rectangular hole, and the upper die is the actual upper edge of the hole- carved to a proper wedge shape.
The piece to be bent is placed between this edge and the bottom die, and the jack is pumped.
Currently, the bottom die accessory I made for the sheet bender has support points an inch and a half apart, and the piece to be bent is just laid across them and pressed into the gap until the right angle is obtained. This makes for a fairly rounded bend and I want it to be tighter.
I have never needed to bend any bar wider than two inches, but by making the opening in the steel plate wide enough for the base of the jack to fit inside of, the capacity would become about 4 inches or so. I cannot forsee needing to bend 1/4 inch thick flat bar that wide, but if I could bend 2 inch wide x 1/4 thick, I'd be happy.
Questions are - how much of a jack do I need, what's the best way to make the bottom die, and would I or should I make a replaceable top brake bar? Also, how wide of steel should be left surrounding the hole in the plate- assuming 1/2 inch thickness? Does it need to be that thick, or would 3/8 be more than enough?
Currently, the sheet bender is using a 6 ton jack, and I have no problem bending 3/16 by 2 inch flat bar to an estimated radius of about 1/2 inch. It's built the same way- in this case it's 1/4 inch plate with a rectangular hole cut out of the center for the jack and bender parts to fit in. It is stabilized by pieces of angle iron bolted all around the opening. I would do the same with the smaller, thicker one.
I would like to rely on the jack post to stabilize the bottom die, also using the sides of the opening to keep the bottom die aligned with the top. There's no rocket science here.
If I need a tight bend I heat the material at the bend to red, trap the heat with water so the width of the red is about the thickness of the metal, and bend using a hammer to bump the bend square and compact. I get nearly a sharp inside angle bending 1/2 x 4 flatbar.
Takes a LOT of heat quickly applied. Heat from both sides. I made a "comb" heating tip. A tip with a row of #24 nozzles every 1/4". Light it and you get a 4" wide flame.
Some good basic info > HERE
Tonnage req'd for vee air bending > CHART HERE
If you want really tight bends you need a coining die (top vee stamps job into bottom vee ) not air bending, + heat the job & work fast
Don't waste your time with a bottle jack, its too slow , use a fly press.
I use two pieces of round stock welded to a plate for my bottom die. The bottom die acts like it gets smaller the farther you bend. I get very crisp bends done cold.
There's some good ideas, thanks. It would appear that a 10 ton jack is plenty adequate for what I would be doing.
Heating at the bend is more than I wanted to do, but thanks for the reminder of that. That's what I've done for the toughest bending jobs so far, without using a machine of any type- just the vise.
As far as a fly press, I use a crude version of that- a heavy hammer and a piece of heavy rail Usually I use that to un-bend when I've over-bent. I did at one point have my own version of a fly punch- a swinging hammer operated by a foot pedal, smacking a spring-loaded punch. Suddenly, this has given me an idea- why not have a gauge on the bender to have a reference point. Make a few tests, then follow the gauge to make repeat bends to the same degree every time- got to keep that one in mind-
I also like the two round bar idea- seems it would have the potential to leave the least markings on the piece being bent. Could also be made adjustable by turning a cam on each end of both pieces, and mounting them in a cradle of some sort- hmm. Could be a good way to get a bend tighter than 90, which would normally not be possible with the typical 90 degree V, and accommodate various thicknesses of material at the same time.
Originally Posted by darryl
The max angle depends on the top tool. Ive used a 12° top tool which would give a bend of 165°, almost back over on its self to form a hemmed edge
A variation on the 2 bar vee - http://www.youtube.com/watch?v=FIQvW...eature=related
Mark free bending - http://www.youtube.com/watch?v=jlR3I...eature=related
Fly press - http://www.youtube.com/watch?v=yo2FcOTzQ9M
Last edited by jugs; 05-27-2011 at 10:25 AM.
I put flat bar in the vise and beat it over with a hammer for a bend. Closer to the vise you hit the bar with the hammer the tighter the bend.
The fly press- that's not what I had envisioned it would be. I thought it would be more like a spinning flywheel which would catch a push rod type of thing to do the punching or pressing.
The mark free bending sure is interesting, as is rounding over a corner. One thing this has given me is the idea to make the upper part a separate piece, so I can choose the type of bend I would make. I think I'll drop the idea of making a rectangular hole in a piece of sheet, and instead I'll build it up from angle and make the upper part removable and adjustable to accommodate whatever bending accessories I might make for it.
Heck, I started out wanting a fairly simple and compact bender- now I have all these ideas- thanks a lot Jugs Just kidding- I'd like to be making it more versatile anyway.
Okay, not an exact answer to some of your questions, but if you want a nice tight radius bend for the size of metal you mentioned here's how...
Originally Posted by darryl
On the 2 inch side of the strap, use a bandsaw to notch halfway (1/8") into the material on what will be the inside radius. Then bend by hand and weld shut. If you really want it to look nice, take a few passes across the weld with a grinder. The final radius will be a little more than the thickness of the metal.
If one wants a square edge on the outside then cut halfway thru on the outside of the bend (the kerf of the blade will be enough for this) and weld. You'll need to grind the edge square but that won't take much time.
This method works great especially if one is making something that needs to be very accurate!
I worked at this one place long ago where we made a large V block which sat on the table of a manually operated arbor press (forgot the tonnage). We added a male V adaptor to the ram side which had a slight radius at the point. The male and female V's were aligned and the base locked into position. After aligning the male edge of the V to a line scribed on the bar we'd simply use the force of the arbor press to bend the bar. I distinctly remember an occasion when I bent 1/4 CRS X 2" wide this way. (No heat was used)