Bending tubing to a specific radius

[quicksandfarmer]

I've been thinking about building a hoop greenhouse. I've been reading on the web about bending 1-3/8" fence top rail into hoops, there are several places that sell simple bending jigs that are not expensive. For example, here: Greenhouse Hoop Benders

The problem with the jigs is that they're set to predetermined sizes, which may not match the size I can get covering material in. So I've been thinking about making my own jigs. (This is the Build-it-yourself forum after all!). The question is, how do I size the jig to end up with a specific radius? It seems to me like the jig has to be smaller than the desired radius because I'll bend the stock to fit the jig and then it will spring back when I release it. Also, it seems like the shape of the jig is not a section of a circle but is instead a section of a parabola. Is that correct?

I've also looked at the Harbor Freight tubing roller (Tubing Roller). I can see how once I got it dialed in I could make exact bends repeatedly. But it's more money and it looks like it would be more work for what I'm doing.

Thoughts?

Thanks.

 

[davesl708]

A conduit bender would give you the most accurate radius. It will take a little practice to get it the way you want it. A jig made from 2x and plywood will work as well. You can adjust the radius on the jig to get the desired radius then bend the rest.

 

[jhasafety1]

I have built several greenhouses for people, I just order a carport that are common everywhere and don't have the tin installed. They work great and fairly inexpensive.

 

[Mysfyt]

Forming metal is somewhat of a black art. Tubing of the same dimensions but from different manufacturing 'runs' will bend to different radii. The composition of the metal, the rate at which it cooled, even how it was handled before it reached your hands are all factors.
I'll boil it down for you. Buy extra and experiment with a couple of bends to dial it in. I'm assuming you're going with a thin wall tubing that you can bend by hand like in the green house video. If a semi circle takes care of your needs, a simple jig that is slightly undersize which you will determine by doing a practice bend and adjusting from there will suffice. If it is parabolic, same idea but you will have to clamp it at certain points to retain the shape.
Roll up your sleeves and have some fun with the challenge. No need to overthink this.

 

[PILOON]

At one time the better half wanted plant hangers to attach to the porch railings.
I used an old brake disk, welded ears and a loop to hook 1/2' rods.
Clamped the disk in my vice, inserted the rods and pulled to form a 1/2 circle.
For a hook I welded a section of chain link that was cut open to accept the wire pot hangers.

 

[Mendonsy]

It might be worth checking around your area to see if there is a metal shop with a roll bender. Once the bend radius is set they could run off the whole batch of material for you in a very short time.

 

[hr3]

I made one years ago to do the same thing. We have a Greenlee 880 at work but it couldn't do the big radius I needed. So I duplicated it in a bigger scale with plywood and 2by 4's and a piece of 4by4. Worked great.. Made a 30' wide greenhouse.

 

[bigtiller]

Make a template with 2x4's and plywood. Set it on some sawhorses so it is east to use. Bend some electrical conduit until it matches the template profile.

 

[quicksandfarmer]

Roll up your sleeves and have some fun with the challenge. No need to overthink this.

That was the answer I wanted to hear! I suspected it might just come down to trial and error but there's a lot of collective wisdom here so I figure I'd tap it. Thanks to everyone who responded.

 

[Stimw]

I made this house a few years ago using 3/4" PVC which bent easily and I fastened the ends to keep the shape.
I bought the good plastic to cover it.
Here in Florida if you do not go the extra step for climate control the house can be 35* in the morning and 150* by mid day!
If you goolge you will find plans and examples.