Monday, November 17, 2008

Ohhhhhh Boy! . . . Chain-Stays!

Today's lesson: It's well worth the money to just buy the pre-bent chain-stays. However I am richer for the experience.

My first idea was to bend 3/4", 4130 into chain-stays. Not having experience I decided to ease into things by bending the tubing on something with a big radius. So I'll use the mandrel from the Superbee . . . and my favorite . . . Rachet straps!

I got some pretty good bends, but the radius was still too big. I replaced the wood mandrel with a 2x10Lbs. plates (Not Pictures, but the result is . . . see below)


OK . . . so back to the metal supply store for more 3/4" (19mm), 4130. ($8).

I went to the bike shop, then flatened the entire length to 16mm x 21mm? If I flatten it some, I can gain 6mm of clearance. It was a painfull act. I paded the vise with 2 layers of inner tube rubber, then squeezed the tube (Cold Set) till it was 16mm width, then moved the tube about 3" and did it again, and again till the whole length was 16mm. Everybody at the shop was surprised how well it went.

The next step is to fill and pack the tube with sand before bending. The sand will support the inside of the tube to keep it from buckling, like the last tube did, when I put a tighter radius on it.

Flattening the tube will also make it easier to keep the bends coplanar. Well that was the idea because I'm only going to put 1 bend on each stay instead of 2.

And they are done. Tommorow it will be time to clean them up, and tack them on to ensure the tire clears, the chainrings clear, and the cranks clear. All the measurement I took suggest they will all clear, but some how when its "In Reality", things change some.
Bending 3/4" 4130 straight guage is no walk in the park. To put 2 bends in each chain-stay you will need 4 foot of tubing in order to get enough leverage and do it right. Unless you have a tubing bender of course.

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