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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This is a reply to @Meriwether’s post about Oakes.
just an FYI, last time I checked, Oakes Mfg, when I was working there. Jason wasn’t making the dies anymore. Unless anyone was motivated and wanted to put in a big order to make it worth Jason’s time.
just an FYI, last time I checked, Oakes Mfg, when I was working there. Jason wasn’t making the dies anymore. Unless anyone was motivated and wanted to put in a big order to make it worth Jason’s time.
My first post on the forum and thought I’ll share something useful.
Had been wondering how to put a slight bend on my chainstays. I considered of the Vevor tube bender but realised I wasn’t bending ‘tubes’ but tapered and squished road chainstays.
So I devised a simple bender cut from 2x4 pine and a saddle block that worked a treat, so I thought I’ll share it here.
Best to refer to the photo, but I slightly rounded the edge of the bender so that it did not put a kink on the tube. And used the leverage from the longer end of the chainstay to bend it by hand.
The first attempt was with a hollow chainstay, but it resulted in a small kink after bending just slightly. To prevent that, I then filled the chainstay with water and froze it. After that, it just bent smoothly without any deformation.
I used a few rubber bands and cling wrap to seal the tubes. Worked well as it let the expanding ice pop out on both ends, relieving the stress on the tubes.
Difficulty in controlling the radius of the bend would be the drawback of this method, but it was as tight as I needed it to be.
The chainstays were tapered chromoly steel with a 0.7mm constant thickness
I’ll try to post more photos, but at the moment, I’m allowed to post only one photo as a new user
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Hi, I’m wondering if you’re located in Toronto, and are building frames.
Hi there. I am in Toronto and I do build frames. How can I help?
I’d like to have a call with you to discuss.I’m at 647-449-9115.
Thanks,
I’m looking for a builder for an improved prototype of a road bike I’ve designed that requires a few bent tubes.