Internal mandrel bending is always the best if you have the option!
Next challenge. 22.2mm Chainstay with 0.7mm wall thickness. Tried to use this die i found in the workshop. but result is super bad…
See the construction in the video-
Radius of the bending die is: 82,5mm
That would work if you filled the stay with bending alloy, such as Cerrobend. There are other brands too, the one I’ve actually used was Belmont.
It’s a finicky process, would slow you down terribly if you’re trying to make money at it, but the results are terrific. The alloy is re-usable, essentially forever. Not cheap but not horribly expensive (I don’t remember, but I was poor when I bought it.) You don’t need to fill the whole stay, just some distance past the bend. An old coffee urn will suffice for “equipment” purchases; the stuff melts way below H2O boiling point.
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Nice idea! But yeah I tried to make money with my bikes… so I need a repeatable solution..
That’s a really thin tube to bend at that radius. Your bender has to be dialed in to hold everything tight. I suspect the tube slipped out of the holder causing the kink. Also the roller on the follow block should be tight up against it. You need a larger radius die or perhaps some internal support as suggested. Have you tried a thicker wall tube?
Hadn’t tried a thicker tube. because my goal is to built a performance bike. Internal support with sand maybe?
I have had reasonable success with filling tubes with sand. (in my case 9.5mm OD, 0.9mm t, 4130)
I thread both ends and screw bolts in to stop the sand moving around. Doesn’t add much time to the process, and stops the tube collapsing.
The tube doesn’t stay 100% round, there is still some deformation - but it’s acceptable (to me) - and repeatable. Without this the tubes were collapsing.
I’m not sure how you’d bung the ends of your thinner wall, larger diameter tubes to keep the sand in place though.
But yeah I tried to make money with my bikes… so I need a repeatable solution..
because my goal is to built a performance bike.
The answer is to buy a mandrel bender.
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