MetalGeek : Code, Metal and Cleverness

Most people seem to think that you need expensive machinery or heat to bend metal. It isn't generally true. Basic bending can be done with nothing more than ordinary shop tools, a bit of elbow grease, and some ingenuity.

Somewhere around 1978, I took a theater materials class and learned how to weld. As part of a sample prop I'd decided to build, I needed to make some 3" rings out of 3/8" steel rod. The only way I could figure out how to bend them was to weld the rod onto a piece of pipe, clamp it in a vise, and twist it around the pipe. Before I did this, my teacher walked by and told me I'd need to heat up the rod with a torch in order to bend it. "Oh yeah?" I replied, as I wrapped the rod around the pipe three times. I suppose I've felt a certain smugness about my metal mangling abilities ever since.

When I first started working in professional theater shops, the only way I saw metal tubing bent into shapes was by cutting partway through the tubing at intervals, bending it, and then welding the kerfs closed. It's a simple method that's easy for a hack like me to understand, but it's tediously slow and usually produces a weak and ugly product. And welding the kerfs closed causes a lot of warpage, so you never know exactly what you'll end up with.

Paying a vendor to do roll bending is one alternative, but it slows down the creative process, and it's not useful for artsy shapes or ellipses. Machines (unless they are very expensive) usually only bend one radius at a time. You end up having to weld a bunch of pieces together, so it's not much better that the kerf and weld method.

After years of frustration with this, I finally saw someone bend tubing with a homemade jig. It seemed magical at the time, but it took me a few more years of intermittent fiddling to understand the process well enough to be able to produce consistent results. In the years since then, I've learned a lot more through trial and error. And spilling some blood. I hope that the following ramble will help you understand the process and its pitfalls a little quicker than I did.

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A Word of Warning

I mentioned blood. Metalwork is dangerous. You will hurt yourself. How bad is up to you.

Bending metal requires some strength, but mostly it requires that you figure out a way use the metal you want bend as a lever to bend itself against a form that may be destroyed in the process. When that happens, you need to be prepared for the outcome. Flesh is weaker than metal, and concrete is harder than your ass or your elbow. If you do much of this, all these things will become acquainted with each other eventually.

Consider yourself warned.

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Tools and Jigs

What sort of equipment you'll need for bending depends on the size of the tubing you want to bend. For anything 1" and up, you'll definitely want a sturdy, well braced table bolted to the floor. You can get by for a while with a plywood top, but it will eventually get destroyed. My table has a 1/4" steel top, which allows for permanent holes for jigs and stops that won't tear out without serious abuse. This will work well for any bending up to about 2". For anything heavier than that you'd probably better call a professional anyway.

I've mostly always used 1/2" steel pins and bolts to locate the jigs. 5/8" would be better for heavy bending, but it isn't usually necessary. Bent pins are easy to fix or replace. A few large C-clamps will help keep the jig from slipping and tearing out the holes.

Spend some time thinking about where you're going to bolt down the table. Ideally, you'll want at least a 20' radius (from the jig) of clear space on two sides of the table, and a good 10' on the outfeed side. The best way I've found to anchor the table is 1/2" threaded rod and anchoring cement. Normal anchors, even big ones, always seem to fail after a while.

You'll also need a heavy duty stop to hold the tubing against the jig and a bunch of holes in your table for bolting it down. The stop and the jig must both be extremely square to the table or the tubing will twist. My favorite stop is made from a very heavy piece of 1-1/2" tubing with a bit of pipe welded on the end. The holes are offset so that I can swivel it to get a tighter fit against the tube.



One other tool that's invaluable is a sturdy router with a large trammel. Routed jigs will bend smoother and with less kinking or twisting than a jig cut with a jigsaw. If you can't get your hands on a router, just make sure that the cut is as smooth and square as you can make it.

Your trammel can be anything you want, but basically what you need is to attach a stiff bar with holes in it to your router. It can even be as simple as a strip of plywood. Most routers have plastic plates on the bottom that can be removed. Just use those screw holes to mount the trammel. I've made trammels up to 35 feet long, but I have to admit that was pushing the envelope.

The jig material that I use the most is 3/4" medium density fiberboard, or MDF. 1" or 1-1/4" is even better, but I don't have a convenient source for it. 3/4" plywood will suffice, but you might have some trouble with kinking, as it's not quite as consistent as MDF.

3/4" MDF will make a perfect jig for 1" square tubing. For 1-1/4" or 1-1/2" square, you'll want to prop up the jig with some shims so that the jig is more or less centered on the tubing. With round tubing, centering the jig is even more important. If the tube is too heavy, or the jig too soft, round tube may destroy your jig. One way around this is to bend a thin strip of steel to protect the edge of the jig.


This is 1-1/4" MDF and 1" tube

For bending big tubing or pipe (like 2" tube or 1-1/2" pipe), you'll want to use a steel jig. The easiest way to do this is to bend two pieces of 1" tubing with a wooden jig and then weld and brace them together. This is actually better than a bent 1 x 2 because it's more consistent and the seam between the two pieces of 1 x 1 is the contact point where the 2" round hits the jig. And since the jig is 2" thick, it's the perfect size for a different sort of end stop. Just take some 1/4" x 1" strap, make a U around a piece of 2" round, and weld it to one end of the jig.


Some jigs

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Small Bends

Homemade hand-bending may not be the best technique for really short radii. For example, 1" x 1" - 18 gauge steel tubing can be bent to a minimum diameter of about 30" before it starts to kink. This isn't an exact number because of the differences in temper and metal quality. And there are a couple of ways to cheat that number even lower. The easiest is to bend several times using successively smaller jigs. How far you can take this is something you'll have to find out for yourself. The other way, which only works for square tubing, involves pushing in the inside wall of the tubing. Here's a 5" radius jig I made for 1" tube that works like a conduit bender.



This does cause some distortion, but the tube retains most of its strength and it's a pretty darn fast technique. The ridge inside the jig is only 1/8" square wire, but the tube wall collapses about 3/8".

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Manual Power

If you're capable of lifting 100 pounds, you shouldn't have much trouble bending tubing up to about 1-1/2" by yourself. For 2", a friend is usually necessary. Spend some time thinking about how you're going to land when something breaks. Something will break. You will end up on your ass.

The forces involved in this may not be entirely obvious at first. In addtion to the weight of the metal and the force that you're exerting, don't forget about potential energy. The metal being bent is a potentially dangerous spring that really wants to smack you in the head. If your jig gives way, metal and jig parts can come flying off the table with surprising speed.

Cheater bars can help you make difficult bends. But they also increase the danger. Landing on your ass with both a 50 pound piece of 2" pipe and a 2-1/2" cheater bar heading for your face is not where you want to be.

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Some Tips

Bend with the seam toward the jig. The weld seam is a little harder than the rest of the tube, so there will be less chance of twisting or kinking if it's on the inside of the bend. And it's usually less visible there.

If your floor is too slick, you may not be able to push hard enough. A very light misting with some nasty spray adhesive will help.

Use the tools that are available. Difficult bending can aided by the proper application of a forklift. Jigs can be mounted vertically on shop pillars so you can use your body weight. It looks silly bouncing up and down, but it's effective.

It's always better to slightly overbend than underbend. It's easier to pop it back out a little than to bend it just a little farther. A stub of 2" tube welded to your table 2" off the floor gives you a convenient notch to unbend your mistakes.

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Bending Data

Metal always springs back from the jig. Here are a few charts that show results I've gotten. Some of the data may not make sense, and some of it may be wrong. Metal hardness can vary, even from the same mill. Aluminum is more unpredictable than steel.

Hopefully, these numbers will give you an idea of where to start. If you have a better idea, just let me know.

Happy bending!

* All material is steel unless noted otherwise.
* Frequently, bending using progressively smaller jigs will produce slightly larger radii than if you just use the smallest jig first. It's just one of the weird things about how metal reacts to force.

1/2" - 20 ga. round tube
desired outside radius	jig radius
144"	54"
120"	50"
32.5"	25.5"
30"	24"
27"	22"
21.75"	18"
21.5"	17"
19.5"	16"
12"	10"
1" - 18 ga. square tube (Central Steel)
desired outside radius	jig radius
192"	108"
144"	85"
114"	75"
96"	65"
80"	60"
72"	55"
65"	50"
58"	45"
53"	41"
49"	38.5"
45"	37"
42"	35"
39"	33"
37"	31"
35"	29"
33"	27.5"
31.5"	26"
30"	25"
29"	23.5"
28"	22.5"
26.5"	21.75"
25.5"	21"
1" - 18 ga. square tube (MetalMatic)
desired outside radius	jig radius
67"	50"
49"	38.5"
34"	28"
29"	25"
24.5"	21"
1" - 14 ga. square tube (Ryerson)
desired outside radius	jig radius
456"	144"
300"	120"
258"	114"
240"	108"
228"	105"
216"	102"
126"	72"
108"	66"
90"	60"
72"	50"
42"	34"
39"	29"
31"	25"
17.5"	15"
11"	9.75"
1" - 14 ga. square tube (Discount)
desired outside radius	jig radius
168"	96"
158"	90"
104"	66"
63"	47"
60"	45"
57"	42"
34"	26.5"
22.5"	19"
18.75"	16"
1-1/4" - 14 ga. round tube
desired outside radius	jig radius
33'	12'-6"
20'	10'
16'-6"	9'
15'	8'-6"
14'	8'
13'-6"	8'
12'-6"	7'-6"
12'	7'-6"
11'	7'
10'	6'-6"
9'	6'
8'	5'-6"
7'	5'
6'	54"
5'	52"
63"	50"
54"	44"
47"	38-1/2"
44"	36"
42"	35"
37-1/2"	32"
33-1/2"	28"
30"	26"
25"	21"
1-1/2 - 18 ga. square tube
desired outside radius	jig radius
180"	120"
168"	114"
141"	102"
108"	84"
84"	72" first, then 66"
1-1/2 - schedule 40 alum. pipe
desired outside radius	jig radius
204"	96"
108"	68"
132"	75"
67"	48"
48"	36"
2" - 12 ga. round tube (Ryerson)
desired outside radius	jig radius
228"	144"
168"	120"
156"	108"
144"	96"
84"	75"
44"	36"
28"	25"
2" - 12 ga. round tube (Discount)
desired outside radius	jig radius
173"	108"
115"	96"
96"	75"
84"	68"
75"	50"
70"	50"
54"	46"
36.5"	29"
31.5"	25"

These tables are admittedly incomplete. I will update them when and if I've got more data and more time. If you come up with a reliable list of your own, feel free to send it to me.

I keep forgetting the formula, so here it is for posterity.

In PHP, it looks like this:
$foci = round (sqrt (pow ($major_axis, 2) - pow ($minor_axis, 2)) ,4);

And here's a form to prove it:

Major axis      
Minor axis      

Place nails 1.7321 units apart, string is 2 units long.


For a nice explanation of elliptical math and nomenclature, see
http://en.wikipedia.org/wiki/Ellipse