Bending tubes?

[Luke]

I would like to see/hear everyone's technique on bending steel tubing.
I'm sure there are different applications for different pieces.
(i.e. seat stays,chain stays,top tubes,seat tubes)

I haven't tried to bend this thin-wall tube, only heavier stuff on other projects.
(Stuff that isn't prone to dimpling or creasing)
Heat or no heat??
(Dad always said that I would go straight to hell for bending cold metal.)LOL

I've seen some fork jigs,etc.etc. Bending one piece would be a challenge, but to bend an opposite matching pieces would take some planning and skill. yes?

Perhaps there is a thread already...or not.

Thanks in advance...
Luke

[fortyfour]

If I was going to give only one point of advice for bending thin walled tubing, no matter what bender, whether homemade or mass produced, the tube must be full supported around its circumference at the point of tangency. This makes or rather wrinkles any good, bad or homemade tube bender's ability to bend thin walled tubing.

One comment would be to understand what is going on with the tube as you bend it. Simply put, when you deform or bend something, material needs to go somewhere. If the tube is to stay round in it's entirety the length of the bend, you are effectively moving material around. The material on the inside of the bend is thickening while the material to the outside of the bend is thinning. This is a good reason why fully supporting the tube at it's point of tangency is paramount.

Bending matched pairs of any bend takes practice and understanding how the material "reacts" to your applied force. There is a definite "feel" and this only comes with practice with the material. It also takes practice when compensating for spring back. Working from a full scale drawing really helps. In terms of methodology, having a way to accurately keep the tubes in phase is helpful as well as a series of stops that allows you to "know" where a bend should start / stop. Being able to measure/read the angle of the bend is another helpful aid.

I cannot comment on heating tubes to bend them as I have only ever bent them cold.

Never underestimate the amount of force you're going to need to bend thin walled tubes. The base you mount your bender to must be robust and have the ability to resist rotation. If you build your own, this is another good reason to over build it. Mechanical advantage in the form of a long lever arm is what I like to refer to as my "persuader". Tubes don't want to be bent as they will resist you throughout the process. They need gentle persuasion.

Hope that helps.

[Luke]

Good advice...thanks 44!

[fortyfour]

No problem. You can call me Kris - Have to amend my signature. Expect to have a bucket full of mistakes. I do. I learn something each time I bend a tube.

[jon_norstog]

Guys,

I've tried a few different bending tricks. Most of what I bend is chainstay and seatsstay material, straight-gauge aircraft tubing. I had pretty good luck bending 5/8" tubing for seatstays (4-8 degrees) using a conduit bender from Ace. for larger tubing and larger angles, I would heat-bend. I use 2 pieces of the next-size-up x .058" tubing to hold the work piece and as a handle, mark it with a mica stick and, very carefully, heat the tube inside the area marked for the bend. It takes a while to get the hang of it. The downsides are two: it's almost impossible to bend two stays identically and the temper is drawn from the heated area.

I bought a Hossfelt-type bender about 10 years agon and mounted its pedestal to my shop floor. It will cold-bend most of the stays I spec but sometimes leaves ripples on the inside of the bend. It helps to lube the dies when you are bending.

I use a 7/8" chainstay on a lot of my bikes. If I am going for a short rear center, that means a radical bend in the chainstays. I broke down and had 100 stays bent on a mandrel-type bender by Tube Bending Specialties in SoCal. It was cheaper than having them made in Taiwan and they used milspec tubing. I can use these stays for a number of different bikes, doing the second bend on my Hossfelt.

I looked around and decided to get some small-tube benders. I plan to order the Baileigh RDB-25 set. It has a bench mount and interchangeable dies. Shold be just the thing for racks.

For forks I made up a bending frame with two grooved wooden dies, 10" radius. I bend my forks after I have brazed in the legs. Works so far.

jn

[Luke]

Thanks for the additional input, Jon.
-Luke