I would like to get some 20' x 1/2" rebar and bend it in an arc to form a greenhouse. I once tried to bend a 10ft length like that, and it bent sharply in the middle, which looked stupid.

Are there any special methods, tricks or relatively simple tools that will help with this?

You could make a jig but that would require welding or a jig table or some real creative thinking with wood. Jig + Heat would look the best.

Or you could use an oxy/acet torch and heat it then bend... since it's 1/2" you could probably get by with MAP Gas torch from home depot... or maybe even propane since it's not much cooler and 1/2" round rebar is not the strongest

Get a conduit bender and slowly work the bend down the length of the work piece.

Susan, make sure you remember to breathe while bending and twisting the rebar.

Like Todd said. A small MAPP torch might be JUST enough for 1/2" rebar but it would take a long time to heat up and in fact might not work very well at all. So acetylene is your best option. Pretty much the only efficient option unless you have access to a portable gas/coal blacksmith forge.

The way I'd do it: clamp one end in a big, heavy, securely mounted vice. Mark the rebar with chalk or file a notch in the middle. Heat the spot until red hot at least, preferably bright yellow, then bend around something round and made of steel. If you need a sharp bend, heat only a localized spot. For a gentler curve heat a longer length.

That said, if you need more than one element you'll probably need a jig to ensure a consistent bend. You COULD do it by eye & hand but it takes practice and some skill to do it right.

I humbly suggest you forget the torch.

A shape like that would normally be formed on a metal rolls. Your local welding shop or metal railing fabricator probably has one. Rebar may not run through the rollers smoothly, but mild steel round stock is cheap and chances are they already have some handy.

The DIY option is to use a stake and some string to scribe a 6' radius half-circle in the dirt. Pound in some stakes along the arc and then wrap your rebar around them. Let it spring back and guess how much smaller your next circle needs to be.

Stay on the INSIDE of the circle while you're bending and keep other people away. !

Buy the tubing for a greenhouse or a canvas garage unit. Will be easier then bending rebar.

I missed the part where you said you wanted an arc not two large bends. Yeah, gonna be near impossible with MAP/Propane, and even oxy/acet w/out a jig will be near impossible to get the exact shape you want.

Get some 1" Square tubing .120" wall and have someone bend that for you. It should be about $1 to $1.5/ft. And if you have a big metal supplier near they may be able to bend it there for you. Then the fun is getting it home bent

If you were local I'd bend it for you... but I think shipping would kill that deal

I've done this - for cement work. No heat needed.

What you need is a bending jig. The one we made was built out of a zillion scrap 2x4's, forming a fanned out arc in the shape we wanted to get it was like laying bricks - we used 18" lengths of 2x4 air-nailed to longer sections of 2x4's that ends of the wood were spaced at about 4" intervals.

Put your hand flat on your desk, splay out your fingers - see how there's sort of an arc formed by your finger? Bend a piece of wire over your fingers - that's the basic idea. Our arc had a section of iron pipe at one end - we stuck the rebar in there and then we simply pulled the rebar over the form - it was hard - until we got the curve we wanted. this was for a project to build a curved concrete wall for a landscaping project.

There are also tools that can be rented to do this, but they are expensive. You set the radius you want and it's got these rollers that pinch the bar and roll it through. You can do small bends and large curves.

For a cheaper and easier solution you might want to consider Conduit.

Sweet, I new someone would have a good idea how to do it with wood

When we jig we use 3/8" plate table, weld on bar stock and make the jig that way. And for small # of bends or doing it in the field oxy/acet works nice

Thanks, Marty! Could your method be used on conduit also?

Conduit normally requires support on both sides as it is being bent otherwise it tends to go oval shape. If you bend it to sharply it will flatten out in one spot. Will work fine with rebar.

If i was making this i would use conduit instead of rebar. Use half or three quarter and the correct bender. If you want a long arc use the bender to make a series of short bends that blend into a long arc. Might take a couple of practice pieces before you like the way it looks. Or you can make a few sharper bends and make the sides and the roof lines flat, easier to bend. And there are all kinds of connectors for joining conduit together. Take a trip though your local electric supply, might give you a few ideas.

Don't know if this is what you want but it might be something to think about.

http://www.shedandshelter.com/syntheticcovering/syntheticcovering.htm

There are several plans made with short section of conduit and the tools required would be a hammer, drill, and a saw.

On a construction project where we have a considerable amount of rebar to bend in a common pattern we would find an expendable slab or flat piece of dry ground, calculate out a segment bend and use a dedicated rebar bender to put a few degrees of bend every few inches, don't use an electrical conduit bender because rebar is a lot stiffer than conduit.

We would draw out the arc we want and do a segment bend, a set number of degrees every so many inches. When we get close we would check it against the arc we drew and add or remove bend as needed. This works for less than perhaps a dozen pieces.

More than that and I would haul the rebar to a welding shop that has a roller bender. A roller bender is, in essence, a set of three rollers that you feed steel into to form a smooth bend. Most commercial welding and steel fabrication shops will have one. Half-inch, #4, rebar isn't really big by construction standards and rolling a consistent bend into it is pretty quick and easy. They might charge you a few dollars a stick. Transportation might be you biggest issue.

I have bent just one or two pieces in a one-off job by stuffing one end into the ground up against a slab or something solid, grabbing the other end, and forcing it into roughly the right shape by leaning into it. If it works your set. The problem is that your bends are unlikely to be consistent. Partly this is just the way of such log-cabin approximations but it also has a lot to do with the rebar. Rebar is usually minimally processed scrap metal and is very inconsistent. One part of a stick can be pretty hard and another, just a few inches away, very soft. Trying to bend the piece in one forced move usually means the soft spots bend and the hard spots stay straight.

Lacking an appropriate bender we have used a sledge hammer pounding the bar suspended between two pieces of heavy steel, the bumper of a heavy truck, or driving the truck onto the bar spanning a concrete curb. Anything to get a few degrees of bend. And then repeating this every few inches according to your segment bend calculations.

it can also be done by making a simple jig - 3 vertical posts in a triangle put the rebar across two of the posts on the INSIDE of the triangle, and take a jack and press from the 3rd post to the part of the rod between the other two posts (bending it out slightly, release, slide bar, jack, etc - it's the exact same principal of the "3 roller" benders that someone mentioned

Another slightly brutal method is to lay it across a couple of boards with a gap between them and beat it with a sledge or stand on it between the boards.
It is not quite as controlled as a bending jig but will get the job done.

Another way is with a hickey.
A hickey is like a big crowbar with a hook and a shoe on the end to grab the steel and bend it using the bar as a lever. The sho is usually separate and a steel pipe is the handle.
They are usually used for bending electrical conduit. You can rent them from tool rental places if you have to.

Here's another crude method that works.Dig out the Arc you are trying to establish,into the ground,then lay the rebar over the trench,& while someone is holding each end(with Leather gloves)Step on the rebar towards the middle,& kind of jump on it,until you acheive your wanted shape,also while standing on it in the center,have the other 2,at each end,push towards you,to acheive the arc,& should you pass your objective,it can always be pulled out,by laying the arc on the ground flat,& pulling from each end,kinda' like a Giant wishbone,until you reach your desired Arc.This method works,& is cheaper than a case of Ranier Ale! Good Luck

I don't think that the jig method would work with conduit as it tends to fold flat. a regular conduit bender might be better, but it won't make as nice an arc - it would be lumpy.