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rethreading a hole on a bicycle

G

Guillaume

Guest
Hi !

I'm in montreal, and I got a bike screw stuck in my bike frame, I've mostly drilled it out, tried screw extractors and such, to no avail. The hole I drilled in is off center, and I started eating the threads on one side. Its on the bottom of the back triangle, so its an annoying setup. I can't seem to find any machine shop willing to do such a small job. I can offer like 20$ or whatever you think is fair payment for it. Lemme know your contact info I'll get in touch !

G
 
Hi Guillame. Most of the guys on this forum are in/around Calgary & surrounding area. Shipping your frame anywhere would probably cost $50 one way, so kind of puts a $ damper on things for you right away. As a suggestion (assuming you are running out of options) is using something like a Dremel with a carbide burr & basically grind out the screw remnant. If the threads are messed up to the point you cannot re-dress them with the appropriate tap, you might be able to tap a larger size & Loktite in an insert like a Helicoil. But that involves another special tap & may not be great on thin walled tubing. I would suggest of you haven't already, visit a bike shop. They may have seen something like this before & have some tricks of their own. At least they will have a better opinion. If the screw is low load like to mount an accessory, that's different than high load for part of the driveline etc.
 
Is it a steel frame? Is it the attachment point for the derailleur, disc brake, bike rack or a chain tensioner for a single speed wheel?

Depending on where the screw is stuck you may have different options.
 
Hi !

Its just the luggage rack mounting point on a steel bike. The screw is known to be M5, so I've ordered a set of cheap metric tap from aliexpress so I have M5 and M6, tool stores in Montreal rarely ever carrying anything metric. I'll look around for sub-1/8" carbide burrs or files and hopefully I'll get an even hole so I don't get a stuck screw and a stuck tap.

I just needed to repaint by bike for the winter, and now I'm getting deeper and deeper in metal working :D.

Thanks so much !

G
 
I find half the battle of screw extractors is getting a proper hole & bite to begin with. Center popping & drilling the end of a broken fastener is a bit more challenging if it sheared at an angle or rough finish. The Dremel grinding burr might hopefully allow a new center. Try to peck drill with the burr vs. holding constant pressure like drilling, they typically don't like that much & can zing off. You might be able to then advance the new conical center with a good drill. Fasteners aren't typically fully hardened by they can be tough.

A lot of lugs like that are braze-ons (or I guess weld-ons if the frame is lighter alloy). So once you get stud out you don't have much choice but to properly drill & tap to larger size if threads are too far gone. Helicoil involves yet another tap.
 

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If you drill it out and it is not perfectly centered many bike racks can still be reattached as most have some play in them. You just need to use a bolt with a nut.

If it is not an option I would grind off the old rack lug and braze on a new one.

Framebuildersupply.com is a good source for parts. You could also check for a local bike builder who would give/sell you one.

Most bike shops do not carry these parts.
 
PeterT said:
Hi Guillame. Most of the guys on this forum are in/around Calgary & surrounding area. Shipping your frame anywhere would probably cost $50 one way, so kind of puts a $ damper on things for you right away. As a suggestion (assuming you are running out of options) is using something like a Dremel with a carbide burr & basically grind out the screw remnant. If the threads are messed up to the point you cannot re-dress them with the appropriate tap, you might be able to tap a larger size & Loktite in an insert like a Helicoil. But that involves another special tap & may not be great on thin walled tubing. I would suggest of you haven't already, visit a bike shop. They may have seen something like this before & have some tricks of their own. At least they will have a better opinion. If the screw is low load like to mount an accessory, that's different than high load for part of the driveline etc.
Click to expand...
That was a good answer :D
 
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