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Old 07-17-19, 11:21 PM
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Originally Posted by scarlson View Post
They are really hard to make. I wanted the derailleur to be all stainless to avoid necessitating any hydrophobic rust protection (oil or grease), which would attract dust. The stainless square tubing I could find in a decently robust wall thickness said it would fit my 3/8" square inside. However, when I bought it, I found that it has a visible welded seam running down the inside. This meant a lot of file work to remove the weld, which was also harder than the base metal. This was drudgery. Eventually I also filed down the pushrod a bit.

I have to think that René Herse must have used a square broach to make this hole the proper size and uniformly square so he could use milled square stock. I could too, and it would make cleaning up the inside of the tube really quick and easy. But square broaches are expensive. I think I'd be paying between $50 and $100 for a used one, making it the most expensive cutting tool I own, although it's a monotasker. Doesn't feel good.
Why not use round tubing instead of square?
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