Step 1: Getting Started - Assessing the Need
Tube bending springs are available at most hardware and/or building supply stores and are used internally or externally to maintain the round shape of the tube near the bend. If springs can't be had for some reason or another the center element of the bender should have a grove in it to provide a uniform pressure on a greater area of the tube wall.
If you plan to bend wire, no springs or groves are necessary. Keep in mind that a bender will be made for a certain diameter and will need to be changed each time you want to bend a different size wire or tube. This is NOT a pipe bender. If you need one of those, this will not likely meet your needs.
Step 2: Collecting the Parts
1) a base - I used a scrap piece of 2x8 about a foot and bit long
2) a rotating part - I used a scrap of plywood about two feet long (3/8" thick)
3) a stationary part - I used 3/4" plywood for this
4) fasteners - I used drywall/wood screws (screwdriver required)
5) spacers - round plastic/wood/metal tubes of appropriate dimension*
6) a saw - for cutting the wood (preferable a jig, scroll or coping saw)
7) bending springs - these are optional
* Appropriate dimension is approximately any dimension. If you are looking for the absolute minimum (i.e. tightest turn) I suggest picking something as close as possible to the size of the tube or wire without being smaller.
Step 3: Let's Put This Thing Together
Step 2: Cut the rotating piece in two following the side of the circle that is on the "IN" side. The short end will then need to be trimmed down to allow the rotating piece to move from 90 degrees straight up to 90 degrees straight down.
Step 3: Screw, nail or glue the short piece to the base. Using a single screw, the bending spacer and possibly a washer between the rotating piece and the base attach at the center of the circle. Tight enough to prevent a lot of movement but not so tight you can't turn the piece.
Step 4: Cut and mount the stationary pieces using the bending spring or the tubing as a guide. It should be tight enough to prevent movement but not too tight to prevent removal of the tube.
Step5: Pull a piece of tubing out across the bender. Using a couple of short screws that won't penetrate the bottom of the rotating section and a couple of spacers (optional) line everything up for straight. The two screws and spacers should provide an even parallel surface for bending the tube.
-- A special note here: If you want to bend more than 90 degrees don't setup the jig straight. Turn the rotating section up and then setup. This will give you up to 120 with the pieces I have configured. I'd say 180 but the stationary piece would need to be modified to accept the tube on the bend around. If you bend something to 120 degrees it's probably fairly easy to finish the job by hand.
Step 6: Mark out a ruler if you need.
Step 4: Start Bending
When I started the project I had in mind that I needed to make it bend in both directions but soon realized it's much easier to flip the material in order to bend the opposite way. Besides I would have needed to do something much different because a circle has only one pivot point.
If I were building this to bend wire I would forget the spacers and just use deck screws or something like that. I hope you have as much success with this as I did should you decide to make one for yourself.
-- One last note: The spring was easy to remove for angles less than 90 but the 90 degree turns wanted to hold on to the spring. I bet it would be even more difficult to remove if the bend exceeded 90 so keep that in mind if you are planning to go to 120 degrees. In that case a grooved bending element might be more practical. Try making one out of hardwood dowel and carving the groove with a 1/4" drill bit or Dremel tool.