Rotary draw bending
of tubes has little cross section distortion at the bend, and I thought that it would give the appearance I wanted in the subframe and rear luggage racks. Here's a nice diagram I found that shows several tube bending methods.
I decided to make my own bender so that I would then have the capability to make a bender for any size tube or bend radius I might find I need. A minimal design would need a bending die with an integrated clamp die, a pressure die, and a frame.
I found a large block of mild steel at the scrap yard I thought I could use to make a double 1/2" & 3/4" bending die for a 1 1/2" radius. I cut the block down to a square and drilled a hole in the center so I could bolt it to the left over stock I had used to make my lower shock bearing mount. Here's the piece in the lathe almost ready to be turned down.
Once I got the OD turned down I cut grooves of 1/2" and 3/4". I didn't have any full radius cutting tools so I just ground a few left and right hand turning tools to have the proper radius. I had five tools in all to do the grooves, a common center one and left and right radius ones.
Here's the final cutting of the 3/4" groove. After the block was bolted to the mount I drilled a center hole in the bolt so I could support the right side with the center seen in this photo.
Here's the finished bending die with my mount and center drilled bolt.
To simplify the design I decided to weld the clamp die and a handle directly to the bending die. I cut a clamping strap from a thick wall rectangle tube and welded it to the bending die.
I found some 1" square stock to use for the pressure dies. To mill the slots I bought a 1/2" and a 3/4" ball end mill
. Here's the milling of the 3/4" die.
Here's a view of the 1/2" die with a section of tube and the cutter.
I had some rectangle stock left over from my swingarm fixture that used for the frame. I cut these slots to allow adjustment of the pressure die position.
Here are all the finished parts ready for assembly.
And the bender in action. I used some c-clamps to clamp it to this sturdy frame. I put some grease on the pressure die to lubricate it. It doesn't take much to bend 1/2" thin wall tube. 3/4" takes considerably more effort.
After doing some test bends I decided to re-work the bending die, clamp and handle. The final version has the handle between the bending die and the frame, the 3/4" grove as the inner groove, and the handle welded to the other side of the clamp die.
Here's a close-up of some bends I could make.