CLOCKS | INFORMATION HOROLOGY!

Horological hints & tips | July 2003

Removing screws

When repairing very old, neglected or abused clock movements, you sometimes come across damaged or seized screws that cannot be removed by ordinary methods.

Here are some of the remedies I have used in the past, with varying degrees of success. Always start with the least damaging and most reversible, and work your way through to the final last resort method given at the end.

Firstly a check should be made to ensure the screw is not a left-handed thread! These are not common in clocks but reasonably common in watches.

Ensure the screwdriver blade is of the correct size and a positive fit in the slot of the screw-head to enable as much purchase as possible.

Soak rusty screws and relative components overnight in a commercially available penetrating oil or paraffin. A seized screw can be heated with the tip of a soldering iron or a fine flame from a small soldering blowtorch.

If the screw-head is badly mauled or half-broken away leaving no purchase for the blade, a new slot can be filed at 90 degrees to the old one using a screw head-slotting file.

If the damaged screw head is countersunk, or the head of the screw has sheared off leaving just the broken screw seized in a component, the screw should be carefully centre punched, and drilled out to just under the size of the thread. A tapered square steel drift, similar to the tang on a file is then tapped in to try and obtain purchase and turn the screw.

If this fails, a piercing saw blade should be inserted into the drilled hole and two cuts made at 90 degrees to each other into the remaining wall of the screw. It should then be possible to punch out the remnants of the screw hopefully without doing too much damage to the thread in the plate.

If after removing the screw by the above method the threads in the plate have been damaged, the threads would have to be drilled out and re-tapped for an oversize screw, or the hole bushed and re-tapped.

Ian Beilby, UK

Current issue | Sample copy | Subscriptions | Hints & tips