Stubborn Thumbstrap Screws

[Dr. Gold]

Hello everyone,

 

I recently acquired a Lachenal 48 key English (basic learners model, from early 1900's - mahogany sides) and am doing a bit of repair work.

 

The thumbstraps need to be replaced, but I am having extreme difficulty removing the two small screws on the left and right (on both sides of the concertina). I'm having the same problem with the finger rests as well, although the screws are a bit larger and I have managed to get one or two of them to budge. Anyone have any tips on how to get those screws out of there? Any input helps...

 

Thanks in advance,

 

Derek

[Geoff Wooff]

Derek,

have you managed to remove the two long screws that retain the action box cover in place and then it is the two short screws which hold the thumb straps and finger rests that are causing problems?

 

This problem is often due to rust and if so then a very delicate application of 'penetrating oil' could help... applying a tiny drop on the end of a needle directly to the rusted screw threads and then waiting for the liquid to do its work, an hour or two.

 

If you can then turn the screws and apply a little upward lift to the thumb strap plate to help the screws Wind themselves out of the holes it should be possible to remove them without damage to the screws or the wood, hopefully.

 

A very well fitting screwdriver is also important.

Edited February 16, 2014 by Geoff Wooff

[DDF]

It might sound a bit drastic but one way which I have used a lot on antique furniture is as follows.Find a nail slightly with a stem slightly narrower than the screw head,grind or file the point off.Hold the head end with pliers or mole grips then heat the cut end with a blow torch until red hot .quickly place the hot cut end against the screw head for a few seconds to allow the heat to transfer to the screw.Do this a couple of times and the scerw will usually lose it grip.The rust will usually enlarged the hole so you may need a slightly larger gauge screw or glue wooden plug in the hole and pilot drill a new hole. A soldering iron would probably be more convienient but they do not seem to tranfer enough heat rapidly enough.

Not sure if this is an appropriate solution for your needs but it might be of use to some one.Regards David.

[Dr. Gold]

Geoff,

 

Thank you for your response. Yes, I have been able to remove the two long "action" screws with no problem, presumably since they have already been removed a time or two to access the reed pan and action, etc. I assume that the short screws have never been removed, since there was never a need, thus they are rusted and stuck. I definitely appreciate the tip about the penetrating oil and will give it a try. If that doesn't work, then I will have to try David's idea.

[Geoff Wooff]

I like David's idea too and perhaps if handled carefully, as he suggests, it could be THE way to go.

 

Good luck with it ,

Geoff.

[d.elliott]

Please do not use penetrating oil, they will get into the wood and spoil it.

 

Just drill the screws out, the old holes will be rust contaminated and pretty ruined anyway.

 

Dave

[OLDNICKILBY]

Try using a left handed drill slowly. This has in my experience been quite efficacious. You can get one from a decent Engineers Merchant. The heat generated works wonders on the rust. It is always a veritable bugger of a task, but keep trying as experience cannot be bought but must be paid for.I agree whole heartedly with Dave, Penetrating Oil will spoil the ends

[Geoff Wooff]

Obviously my suggestion of a tiny drop of penetrating oïl directly onto the rusted threads, under the thumb strap plate/ finger plate is going to prove an easier method for most DIY concertina fixers than drilling out the screws which is difficult and dangerous for the uninitiated.

 

Anyone who has ever tried to drill out a rusted screw will know how easily this can end in disaster. A tiny oïl stain under a thumb strap is hardly to be noticed.

[Wolf Molkentin]

Anyone who has ever tried to drill out a rusted screw will know how easily this can end in disaster. A tiny oïl stain under a thumb strap is hardly to be noticed.

 

That's what I have been thinking as well. The warning not to spoil the ends with the use of oil had to be issued, but if carefully applied it might be worth a try however, depending on the skills of the repective owner.

[apprenticeOF]

My concern with oil and wood is not cosmetic, but softening of the wood. That could result in difficulties with the screws, possibly even larger ones, not holding. The oil will suck into the end grain of the holes and won't evaporate., leaving soft fibres. And if you need to glue in plugs - you are "done", they won't stick.

 

Petroleum oils and wood are a bad mix in my opinion.

 

Drilling them out is the best, if tricky option. Even if you muck it up, the option remains to go with a larger drill, a new thumstrap plate, and a plug/pilot hole.

 

I'm in Dave's camp on this one.

 

Doug

[Greg Jowaisas]

I'm in DDF's camp, although the blow torch and red hot nail seem a bit extreme to me. I've used a soldering iron to good effect on frozen thumb strap screws and end bolts. It takes some patience and repeated applications of heat, in some cases 4-5 times of heating and then allowing cooling. (You need to break up the rusty adhesion with repeated expansions and contractions.) I use a fairly hot electric soldering iron with a small tip. Some conservative experimentation with a count (20-30 seconds seems to work for me) will get the frozen bolt hot but leaves the surrounding area intact.

 

If that fails I'd prefer to use a Dremel to carefully grind off the head of the screw, remove the thumb strap/plate and then use a small needle nose vise grip to back out the shank of the screw.

 

Last resort for me would be taking the end over to the drill press and drilling the screw out.

 

Greg

[d.elliott]

Assuming the screw is rusted in, and you manage to withdraw the rusted screw stub (by whatever means fair or foul) the screw hole and it's rust contaminated (if not locally spoiled) wood will still need drilling out and plugging so why waste so much time and effort in the first place? but still a few more thoughts.

 

I do agree to the left handed drill approach (see Nick above) but on more substantial screws, a technique I use myself, but on these very fine wood screws which are already in poor condition, there is a more than fair chance that the fine drill will break adding another hardened dimension to the fun and games.

 

Greg's approach of removing the screw head & then the thumb strap to reveal the screw shank to grip onto is always my first step. This works a dream if the initial problem proves to be a knackered screw head, however, in my experience in damp and rainy Yorkshire, this is not usually a success on a corroded screw. Where the screw is corroded I usually find that the shank is not substantial enough to withstand the torque to break the corrosion bond.

 

Whatever happens and however the screw is removed. We need to remember that on the way to the result we cannot loose sight that the forces used must never put a potentially delicate (and aged) fretting at risk, the fretting needs direct support against pressing, drilling, screw driving and turning forces - from which ever side of the finger board they are applied. We also need to remember the endgame: the resultant anchorage for the thumb straps has to be substantial enough for a good and confident screw grip when re-assembling. This without going oversize on screws which will only have equally oversize heads that will show above the thumb-strap leather work and cut at the thumbs.

 

Oh happy days! can anyone remember life before concertina domination?

 

Dave

[DDF]

Another technique which has not been mentioned but can be very useful, if you have got to the stage where the head has been removed.Measure the gauge of one of the screws already removed and find a piece of( preferably )steel thin walled tube with an inside diameter slightly lager than the screws gauge.File or Dremel some teeth/serations in the end.Use this at a fairly slow speed in a drill to drill a hole around the remains of the screw shank.Withdraw regularly to clear the frass.This hole will follow the screw and leave a nice clean hole for pluging.If you have a lathe this kind of drill can be made very acurately and hardened.In a moment of desperation brass tube as used in radio ariels works well but needs a little more care to prevent overheating and blunting.David.

[Don Taylor]

http://www.ericsonyachts.org/infoexchange/showthread.php?9668-Unscrew-ums

 

Scroll down a bit to see a description and some pictures of 'unscrew-ums'.

 

These were developed mostly for the boating world where rusted in screws are common (death to anyone using a common metal fastener!). I have not tried them, but if there is a suitable size for you they might do the trick with minimal damage.

 

I think that the inventor is a one man company, www.tltools.com, and you might have to buy directly from him.

 

Don.

[Greg Jowaisas]

I like David's (DDF) suggestion of tightly sleeving a sharpened tube over the broken shank and boring it out. I'll give it a try next screw emergency.

 

Greg

Edited February 23, 2014 by Greg Jowaisas

[Don Taylor]

I like David's (DDF) suggestion of tightly sleeving a sharpened tube over the broken shank and boring it out. I'll give it a try next screw emergency.

 

Greg

Un-screwums are a commercialized version of this idea. They have saw teeth at the bottom to help cut through the wood, and a slit down the side so that a tightly fitting one will open up just enough to fit around the screw and grip it so that you can pull the screw out when you are done.