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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
 

PeterT

Ultra Member
Premium Member
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.
 

IC...

New Member
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.
 

RobinHood

Ultra Member

John Conroy

member
Premium Member
I would take it to a bicycle repair shop. An experienced bicycle technician will have experience with that sort of problem.
 
G

Guillaume

Guest
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
 

PeterT

Ultra Member
Premium Member
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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IC...

New Member
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.
 

CalgaryPT

Ultra Member
Vendor
Premium Member
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.
That was a good answer :D
 
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