How to unscrew the remnants of a broken screw on a knife

[Rusanv]

Hello everybody. My name is Anatoliy. I'm from Kazakhstan. newbie on the forum. I need help. I bought a used Police knife, two screws are missing (cut off) on the clamp, I ask for advice on how best to remove them?


I believe - the sheared screws on the thread lock.

I would be very grateful for your advice.

[Evil D]

That will probably need drilled out and maybe even retapped. On such a small screw that's not going to be easy. I would see if there's a machinist in your area that might be able to do it, maybe even a jeweler? You'll need a tiny drill to drill into the piece of screw.

[ChrisinHove]

Yikes.

If the knife still functions, I would leave it alone.

[awa54]

A drill press and a very small screw extractor... At least in the US, there are available extractor kits that go down under 1.5mm, so it ought to be possible, but even with the right tools a tiny screw like that will be difficult to extract.

Most jewellers are going to have only hand held flex-shaft type rotary tools, so a machinist is likely the better option.

Welcome to the forum and Good luck!

[Rusanv]

Thank you all for the warm welcome in this forum and for your recommendations. Yes, it will be a difficult task for me. First, I will carefully prepare, then I will try or look for specialists.

[spoonrobot]

Can you get left-handed twist drills?

McMaster-Carr does not ship internationally (you would need to use a freight forwarder) so I am sharing the link to give you an idea of what sizes are available: https://www.mcmaster.com/left-hand-drill-bits/

The best thing to do is drill a hole completely through the screw with a left-hand 1.5mm bit, sometimes the screw will come out during this process but sometimes not. If not, move to a 2.0mm bit, this has always worked for me. In theory a 2.2mm bit would remove the screw completely while also removing some but not all of the threads in the hole. Re-tapping would be required. I have the bits and tap to do this but have not had the need, yet.

The problem is that you will need a very good drill press or mini-mill. The small bits break very easy if used in a hand-drill or a press/mill that has any runout.

Extractor style bits work better for screws with damaged heads, I'd had success with larger fasteners but not with anything 3mm or less. The extractor just doesn't seem to have purchase to transmit enough force. They are relatively cheap: https://www.amazon.com/Damaged-Screw-Re ... 07HGSPQDV/

Good luck, this is not a trivial problem but success should be assured with the right tools.

[z1r]

Milling/Drilling the remnants out is how I would do it. But I have seen a good welder tig what amounts to small "T" handle onto the remnant and then unscrew it.

[Rusanv]

Milling/Drilling the remnants out is how I would do it. But I have seen a good welder tig what amounts to small "T" handle onto the remnant and then unscrew it.

Good day. Interesting idea. Thank you

[Rusanv]

Can you get left-handed twist drills?

McMaster-Carr does not ship internationally (you would need to use a freight forwarder) so I am sharing the link to give you an idea of what sizes are available: https://www.mcmaster.com/left-hand-drill-bits/

The best thing to do is drill a hole completely through the screw with a left-hand 1.5mm bit, sometimes the screw will come out during this process but sometimes not. If not, move to a 2.0mm bit, this has always worked for me. In theory a 2.2mm bit would remove the screw completely while also removing some but not all of the threads in the hole. Re-tapping would be required. I have the bits and tap to do this but have not had the need, yet.

The problem is that you will need a very good drill press or mini-mill. The small bits break very easy if used in a hand-drill or a press/mill that has any runout.

Extractor style bits work better for screws with damaged heads, I'd had success with larger fasteners but not with anything 3mm or less. The extractor just doesn't seem to have purchase to transmit enough force. They are relatively cheap: https://www.amazon.com/Damaged-Screw-Re ... 07HGSPQDV/

Good luck, this is not a trivial problem but success should be assured with the right tools.

Good day. Yes, I ordered small diameter left hand drills. Thank you very much for such a detailed method. It remains to find a drilling machine. I think it won't work with a hand drill.