agenkin

Apologies if this is not the right place for this question, I am not a frame builder and this is about building a rack.

I'm thinking of making custom front and rear racks out of 4130 tubing (8,9, or 10mm OD). I have a TIG welder, but have never welded thin tubing before. I would like to hear from somebody experienced:

1. Are there any tricks to TIG-welding thin chromoly tubing, and
2. What's the best way to bend cromoly tubing into shapes, considering I don't have any jigs. I have a woodworking shop, so I can easily make templates or forms out of wood. Is it better to heat the tubing and then bend, or is it better to bend it cold?

Many thanks in advance!

CliffordK

I bet you could build a reasonable small tubing bender using a lathe.

Cut some discs with a channel down the middle the size of your tubing, and then figure out how to simply bend your tubing around the radius.

unterhausen

4130 should be bent cold. I think 8mm is plenty big for most racks. Ebay is a good source for tubing benders

CliffordK

Also check Harbor Freight. Make sure you snag a 20% off coupon from online.

unterhausen

I don't think any of the HF tubing benders are worth buying, do you have one that you like? You can buy Ridgid, Parker, and sometimes Swagelok benders on ebay. I would stay away from the single tubing size Imperial Eastman benders, don't like the bends they make.

There are a lot of pictures of people making racks on flickr. I always use a bender, but you can also bend around pulleys for larger radius bends.

fietsbob

Mandrel benders, have a plug down the center of the tube, to keep it round as it's bent, ..

shoe benders just support the inside of the bend, you see that imprint , muffler shops, that bend in house use that type..



I have an old Bruce Gordon rack set , he brazed them, later, he paid someone to TIG weld , in a production quantity..

It is not a trick, if it's a skill...







.....

unterhausen

the better tubing benders in the sizes used for bending rack materials don't squash the tube in the bend. It depends on the bend radius and the tubing thickness. Smaller radius bends and thinner tubing with respect to the tubing diameter are more likely to squash. But people bend seat tubes and stays in benders without using anything special to keep it from squashing.

I don't think anyone makes a mandrel bender in sizes like that.

fietsbob

a set of rollers machined to preserve the shape for 10mm/3/8" tubing is always possible...