rounded off screw head

[Scilly Suffolk]

I picked up a Record front derailleur for next to nothing because one of the adjuster screws is rounded off.

There is no room to get a pair of pliers on it: any suggestions?

Thanks in advance.

 

[Red Light]

I picked up a Record front derailleur for next to nothing because one of the adjuster screws is rounded off.

There is no room to get a pair of pliers on it: any suggestions?

Thanks in advance.

Cut a screwdriver slot across the head using a Dremel or some such. Or get a screw extractor - these work well on cross head screws that have been rounded off.

 

[Gary E]

Can you get at the other end of the screw? If so use a pair of needle nosed pliers to wind it out enough to get at the head.
Failing that drill it out and replace it. If you have one, use a cobalt drill and take care to drill through the centre of the screw so that you don't damage the threads in the body.
Those screw extractors are good for larger bolts but not a lot of use on small ones like this unfortunately.

 

[RecordAceFromNew]

Soak screw thread in penetrating oil / WD40 overnight. Cut slot on top of screw carefully using a fine bladed file or saw. Ensure screw is not under compression (e.g. if off bike and L limit screw push against spring, jam something in, to stop screw fulfilling its function) before using a correctly sized screwdriver for the slot to ease it out.

If there is not enough room on top of screw to cut a slot, and if there really is no room even for needle nosed pliers you might have to try dismantling part of mech. Front mechs aren't too valuable, fortunately, even Record.

 

[Scilly Suffolk]

Thanks all.

I'll try cutting another slot across the head, it's too thin to drill out. I've dismantled it as far as possible but that doesn't improve access.

How do the screw extractors work? Do they drill into the screw and then you reverse the drill to pull it out?

 

[Gary E]

No, you have to drill a hole first and then turn them into the hole anti-clockwise. When they bite they turn the screw. As I said, not too bad on larger screws but not a lot of use on small ones.

 

[Scilly Suffolk]

It's only 2/2.5mm across so it would be beyond my skill to drill into it.

 

[Red Light]

How do the screw extractors work? Do they drill into the screw and then you reverse the drill to pull it out?

There are various types but the ones I suggested work by drilling a cone in the head of the screw. You then reverse the bit so the other end with the spiral grooves you can see in the photo goes into the cone. When you turn it those spirals cut into and grab the screw head and twist the screw out. Others you drill a hole into the screw (usually when the head has broken off) and then again the bit is a bit like a tap that cuts itself a thread but, because its tapered, pretty quickly jams itself and starts twisting the screw instead. Both are always worth having in the garage because when a screw breaks off its a couple of minutes job to sort it and move on.