Repairing Woodscrew Threads
By John Phillips
I was very interested to read Ron Schmuck's description of how he got the stubs of broken-off woodscrews out of his organ works. I guess everyone who has pulled a few player actions apart has experienced the sickening feeling of a rusted-in woodscrew breaking off in situ. If they look like giving trouble, I always apply a hot soldering iron to woodscrew heads before doing anything. This helps to break the bond between the rust and the wood. (I'm probably trying to teach a lot of grandmothers to suck eggs here.)
I have used a bit of stainless steel tube, once or twice, in the manner Ron describes, to get broken stumps out. I tried cutting crude teeth into the bottom end of the tube - I'm not sure it was a lot of help, as things still got pretty hot. Brass tube, which is usually quite thin, sounds like a good idea, as long as it will stand up to the mechanical stresses.
There is a problem with plugging the holes with dowells afterwards and that is that the screws will be going into end-grain timber. This means the thread in the wood will be weaker, but what's the alternative? I guess that using hardwood instead of softwood will at least partially compensate.
I have found a similar problem evry time I've taken the valve plates out of an Aeolian action. Each plate is held down by four little screws (from memory they would be about 6 gauge and 3/16 inch long). Every time I've found some of the threads in the wood are stripped and the screw is just sitting in the hole. Here is a method of repairing the threads in the wood without major surgery.
Prepare a small quantity of epoxy glue and mix into it a roughly volume of softwood sawdust.
Dip the woodscrew into grease (I use Vaseline) and wipe most of it off leaving just a thin film.
Half fill the screwhole with the epoxy-sawdust paste.
Screw in the woodscrew until it is not quite as far down as it would be in its working position.
Don't touch it until the eopxy is well and truly set - maybe wait for a couple of days.
Unscrew the woodscrew. The epoxy should have set in a female thread shape around it and the grease should stop the exopy sticking to the screw.
Don't overtighten the screw when reassembling the valve!
The idea of the sawdust is to try to give the epoxy some of the resilience of wood. I don't know how well it works because I've never done any comparison tests between undamaged threads in wood and repaired threads.
I'll just bet that Craig B. has got some comments on this; flex your fingers Craig and give us the benefit of your experience. I'd love to know of a better way. I've sent notes on the above idea to, I think, both the AMICA Bulletin and to the British PPG Bulletin. They sank without trace in both magazines.
John Phillips
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(Message sent Mon 16 Sep 1996, 03:32:03 GMT, from time zone GMT+1000.) |
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