# Bend Metal Without Expensive Tools

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UPDATE:
Check out this super two-person trike my partner and I are offering on Kickstarter! I'll be bending the metal using a jig just like the one in this 'ible.

I'm a big fan of Atomic Zombie's builds. Except I like curved lines once in a while. I don't have access to a pipe bender, but I really wanted to introduce some curves to our latest project. Here's how you too can bend metal without any fancy equipment.

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## Step 1: Determine the Yield Strength of the Metal

I buy steel tube in 20 feet sections. I surreptitiously push on the section to determine if I can bend it. I can feel the tubing start to give, and by sighting along the tube I can see how much the tube has bent. I predicted that I needed about 3 feet of leverage to bend the thin wall square tube I found. In other words, I needed to ensure that I always had at least an extra 3 feet of tubing to use as a lever to push on when trying to bend it.

I'd guess that the thicker walled, 1-1/2 inch tubing that Atomic Zombie likes to use would need about 5 or 6 feet of leverage.

## Step 2: Cut a Jig

I wanted to make a few curves of various diameters, so I created a jig with a variable curve. I cut a 2x6 and saved the cut-off to use as a brace for the clamps.

## Step 3: Cold Bend It!

I know you young kids have never used a French Curve, but if you had, you'd know that you can approximate most curves using some other curve. To use this jig, start at one end of your tube and choose which part of the jig might give you the nearest approximation and clamp everything down. Bend the first bit, move the clamps, and bend the next bit.

## Step 4: Matching the Work to a Template

As you can see,even in primitive conditions expert results are possible!

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## 42 Discussions

i am planning to bend two pieces of mild steel tubing about 1 1/2 inch diameter. would I definitely need an actec-oxy industrial torch or could I get by with just a propane torch? considering mild steel tubing not so much like a heavier gauge piece of mild steel.

this is for a hitch for my bicycle trailer. have a nice weekend, everyone, steve

You most likely don't need to heat the metal at all. The most weight you probably want on a bike trailer is 100# or 45kg so even metal conduit will handle the load. Borrow someone's pipe bender (check your local tool library). There's no need to over think or over engineer the hitch.

Structural engineer here.

What you're talking about in Step One is NOT "determining the yield strength of the metal." Rather, you are determining the STIFFNESS of the tube section.

"Yield strength" is a property of the steel, the stress at which the steel will begin to deform plasticly - that is, it won't spring back into shape when you remove the force. It's a material property unrelated to the geometry of the steel piece you're looking at.

What you're doing in this step is seeing how much deflection results from a given force - in this case from your arm. When you remove the force, the steel tube resumes its original shape because you're still in the elastic region. However, when you bend the tube to form the curve you're talking about in the rest of the article, you've gone into the plastic region where the steel won't spring back straight. There's no way you will come close to that level of force using your arm unless the tube is very thin or very small diameter.

The determining factors for the deflection you're inducing in your "test" are 1) the diameter of the tube and 2) the thickness of the tube. If you know those for a given piece of steel tube, you can calculate pretty accurately what the deflection's going to be without ever touching it,

And if you know the specification of the steel, you can also determine the yield point by calculation.

Thank you for offering your expertise! You've described exactly what I'm doing: pushing on the tube past the point of elasticity and just to the start of plastic deformation. A 20 foot stick of cold-rolled steel up to about .090 wall thickness will deform permanently with just careless handling!

So what I'm doing, without using calculations, is feeling for the moment that steel begins to give way. One just has to be sensitive to the "shoulder" of the stress/strain curve.

The geometry makes a difference because a piece of 1" x 2" tube is much much harder to bend in the 2" direction. I can barely do it with a stick of .065 wall.

Amazing tool use for bending steel bar. I found it useful to be use in construction business. Visit KB Rod Benders (kbrodbenders.com).

This tube is very thin; I recall it's probably .060 or .090, so that'd be 16 to 13 gauge. It's just mild steel, HREW or so. I've bent Chromoly with a jig, but it wasn't pretty. Probably would have made an entertaining video too, in its own way.

Thanks, will have to re-think my strategy. I get nervous when I think of traveling 35-40 mph and having a weld break. The bike path here in RI has a nice canal running parallel. Might go with mild steel and forget the Cromoly stuff.

The real advantage of Chromoly is that a .035 wall tube is as strong as a .060 wall mild steel tube (insert caveats here) while being 40% lighter. I tried and tried to make good welds on .035 tube, but I always blow through. So, at my current skill level, I've got to stick with .060 or heavier. At this gauge there's no reason to spend the extra dollars for Cr-Mo for a bike build.

*If* however, you are cleverly building lugs and then brazing Cr-Mo into the joints, that's another story altogether.

Our current build, this tandem trike, uses a pair of 2" dia .065 wall DOM bottom tubes and it is so stiff we could mount a Harley or BMW motorcycle engine in it. It's ridiculously strong.

Good luck with your project! Are you posting pics of it?

Hey Captain Robert, I am a blacksmith by hobby but a friend whose dad was an ironworker used to bend square and round tubing with heat. jto avoid collapsing the sides he filled it with sand first. Thanks for the instructable I have used this technique with wood but had not though to use it with metal.

I wish I'd seen this a few months ago. I ended up cutting and welding to get the curves I wanted.

Have you used a cheater bar inserted in the tube? Curious in case a guy (me) had shorter stock without the extra 3'...

3 replies

Yes, (I build Lotus super 7 race cars) and when I have complex bends that can not work with my JD2 expensive pipe bender, I pack the (metal) tube TIGHT with DRY (has to be DRY!!!) sand, then weld shut the ends, the build a wood form (as noted herein) using some metal sheet to help the wooden jig last longer since I head the tube red-hot with the rosebud torch (lots of gas) then it bends perfectly. The thin wall tube will just kink without the sand, but the sand is also a heat sink so it's a slow process, but sometimes, that's the only way.