Friday, December 19, 2008

Scrappie: My new tube bender

Yes, he has the same name as the sheep disease. And he's not much prettier to look at, but darn does he make nice bends in tubing (well, seatstays, anyway. I wouldn't want to try to bend anything a whole lot more substantial on him).

Materials were:
- 12" piece of 1" square tubing (scrap bin)
- Various bits of 3/4"x1/8" mild steel
- 2 3" pieces of 1" angle iron
- Seatstay scraps (for cradle pivots)
- Old piece of 3/4" plywood
- 3 wood screws

The lefthand (far) cradle is fixed to the spine of the fixture, but you can move the righthand cradle in or out depending on how far apart you want to support the ends of the tube. I'm honestly not sure if this matters much for the actual bending, but it was easy to make it adjustable, so I did.

The mandrel/form was made with a borrowed jigsaw. It's an 8" radius, and I beveled the edges of the 2 pieces of plywood, then filed out the middle to mimic the shape of a 16mm seatstay. I imagine I'll make a bunch more of these with different grooving and radius, just because they're easy to make and I have plenty of scrap plywood.

The hook (that looks like a little chair) attached to the spine is to hold the fixture in place in the mill vise. Otherwise it's too front-heavy to stay upright, which is annoying. I could probably come up with a more elegant design to solve this problem, but this project wasn't about elegance - it was about getting some tubes bent, and at that, it is a definite success.


Anonymous said...

Nice work!

What in the mechanism makes sure you always get consistent results? (read, curvature).

Walt said...

Anon -

Great question. Right now, I snug the fixture down (without using the handle on the vise) and line everything up where I want it, then simply count the number of turns I tighten the vise down.

I'm thinking of putting a modified depth gauge of some kind on there to make things easier, but the counting turns system seems to work pretty well in the meantime.

It's entirely possible that I'll make a nicer/cleaner version of this (with a few changes) at some point down the road. This was really a proof of concept type of project more than anything.