Stripped Thumb Strap Screws

[Randy Hudson]

The two shorter screws on one of my Englsih thumb strap have stripped. Any advice on best approach?

 

Randy Hudson

[Frank Edgley]

If you contact Colin Dipper, he will most likely have, or make a replacement for you, if it is the thumbscrew and not the threaded insert which is stripped. If it is the insert, he may suggest retapping with a slightly larger size and replacing the thumbscrew with another with the new thread.

[Paul Groff]

Randy,

 

I agree with Frank. But if it is the little woodscrews (on either side of the very long and narrow woodscrew, all 3 of these fastening the right-angled part of the thumbstrap) and not the thumbscrew, the answer will depend on what they are screwing into. If the ends of your instrument are wooden, you (or your repairperson) can plug the holes by glueing in wood, then with a fine drill or awl make new pilot holes to accept the screws more tightly. If the ends are metal, there is probably a wooden block(s) to anchor the screws, and this can be repaired as above or replaced. If you are not sure you can do this, better to take or send it to an experienced repairer. It's not hard but you want to be careful (especially with the ends if wooden).

 

Paul

[Randy Hudson]

Thanks for your quick replys - sorry I did not provide more info. The two screws in question are the two shorter ones holding the thumb strap to the WOOD top of the instrument. My previous experience is that these simply screw into the wood, while the longer one goes through the inner post (it seems fine). I haven't actually taken the instrument apart yet - hoping to do so only once for the fix.

 

I assume the wood holes simply need to filled with something, and new holes drilled. Or possibley the holes need only to be "coated" with something to decrease their size a bit. I would be quite capable of doing this - I'm just asking what the "filler" should be. Would something as simple as epoxy, or perhaps woodworkers glue mixed with very fine wood dust be a simple solution? Or how about using longer screws and a small block of wood behind, like a metal top? - or a combination of the two for assurance?

 

By the way - I am a "newbie" only because I recently re-registerd for the site. I actually have been playing about six years and done simple repairs numerous times. Can a guy get reclassified as "experienced"? I don't really care, but I would think the "newbie" classification affects people's responses.

[Pete Dickey]

I recently replaced the short screws on an Lachenal English when fitting a new thumbstrap. It struck me that it may be better to replace the screws with small brass bolts, washers being placed on the underside to distribute the loading more evenly. This seems to work well.

 

Pete

[Paul Groff]

Randy,

 

I'm sorry if my reply seemed to imply you were not knowledgeable; I only meant to allow for that possibility. *I* am pretty new to this group and so have not entered into discussion with many of you. Re: epoxy, in my opinion this should be avoided. If the little screws are just barely stripped you may not need to plug the holes; you might get way with using a plane shaving (e. g., of mahogany or walnut) glued into the stripped screwhole with some liquid hide glue or aliphatic resin glue (if a sliver projects up or down from the surface of the ends this can be trimmed after the glue dries), to give the threads something to grab. BUT...

 

Peter,

 

I really like the idea of bolts (machine screws) and plan to try it myself next time. What about omitting the washer and insetting little hex nuts into slightly undersize round holes that go just partway through the underside of the wooden ends; that way you could tighten or loosen the machine screw from the outside without needing to hold the nut from the underside.

 

Paul

[Pete Dickey]

What about omitting the washer and insetting little hex nuts into slightly undersize round holes that go just partway through the underside of the wooden ends; that way you could tighten or loosen the machine screw from the outside without needing to hold the nut from the underside.

Paul

 

Insetting the hexagon bolts into the wood might, I feel, weaken the structure a bit too much and could promote splitting along the grain of the wood particularly in Rosewood. Far preferable I think would be to solder a hexnut onto a washer and glue the assembly onto the wood. This should give enough grip so you can tighten/loosen the bolt (machine screw) and should help with pulling forces on the wood. However perhaps Dave Elliott or other like-minded folk have a different view.

 

Pete

[Randy Hudson]

Thanks for the tips. I also like the bolt idea very much. In fact, it seems so logical that I wonder if there is some reason they were not done that way from the start - other than the extra hardware involved. I suppose just to be able to work the screws without taking anything apart, as Paul's suggestion would allow.

 

Paul - I actually hadn't felt your response inferred anything about my newbieness. It just strikes me that it may be useful to be able to "upgrade" - anyone know if this can be done?

[Pete Dickey]

I also took the view that the use of brass bolts was preferable to steel since sweat from the hands would cause corrosion of the steel with consequent expansion which could also split the wood. I used 8BA bolts with recessed heads which I obtained from a model shop.

 

Pete

[Paul Groff]

Peter & Randy,

 

Interesting ideas. I have to admit I usually have just done a standard repair for stripped woodscrew holes, with a little more care since the wooden fretworked ends are a somewhat fragile piece you don't want to damage. But I am very interested to try the machine screw approach. I take Peter's point -- I might have come to the same conclusion when actually surveying the piece prior to any woodworking (always very important). I think the solution described in his most recent post might be the best of all. Again, we'd have to have a good look and a "think" (and think again) as always before cutting or glueing original wood. Thanks for the discussion.

 

Paul

[Dave Prebble]

Hi All,

 

Plenty of sound suggestions there.

Just a couple of points.

The small size screws have very little to grip to and are hard to find new.

This is quite a common problem and really should be 'nipped in the bud'. Once these small screws have become loose or failed, there is opportunity for the thumbstraps to move about and cause flexing of the thumbstrap bracket, the wooden ends and the long screw that runs through the post to the action board.

This leads to the long screw failing* or wearing the hole and pulling through the bracket and in either case very often damages and weakens the wood around the bracket area.

To my mind the ideal is to make a brass plate (for argument say 1" square but make to fit in) with a hole drilled in it to allow it to clear the post and to then secure this plate to the inside of the wooden end. Instead of screws, use small bolts through the thumbstraps either threaded into the plate or bolted through it.

This will acheive the same result as Pete's method but will spread the load considerably - especially important if there are already signs of the wood splitting in this region.

 

Regards

Dave

 

* If this long screw fails your only hope is to get one from of the repairers.

I am told they have not even been manufactured (In the UK at least) for many decades.

If any one out there does know of a source of No 1 or 2 gauge woodscrews in lengths between 3/4" to 1 1/2" , I should love to know.

Dave

[d.elliott]

I usually repair thumb and finger slide attachment (small) screw problems by plugging and using the same or equivalent wood screws. In sever cases I have actualy cut out and fitted new wood tapered inlays, Tapered from the underside so that the scews are not biting onto an end grain.

 

However over the years I have had three or four instances of where the problem had been overcome by using countersunk headed BA, I guess around 8BA setscrews with nuts on the inside of the fretting. Given the tendency to overtighten them, one person had 'double nutted' or lock nutted the screws at the best tension, another had resorted to something like a Loctite 'Nut-lok' fluid to stop the nut un-winding.

 

I also saw that the nuts cut into the much softer wood, and as the inner contour of the wood is not parallel to the thumbstrap plate the bolts are usually twisted over. Eventually this will create a bigger problem.

 

One final problem that I have noticed. The nuts, unless poitioned with a 'flat' tangential to the adjacent pillar had a tendency to provent re-assembly by fouling the pillar. One pillar had been whittled to make clearance.

 

So chaps, fine idea, and definitely the way to go when designing a new instrument, but don't jump at this idea as an instant remedy or super enhancement, it might be more trouble than its worth.

 

Bye the Bye, I have a Wheatsone made Edeophone, (Amboyna burr ended 63key!!!, oops, sorry drooling again) which is about to be returned to its illustious owner. This actually has setcrews/ nuts under the thumbstraps, both thumbstraps had worked loose and these nuts had been Nut-lok retained.

 

Dave

[goran rahm]

Most said at this stage probably...just...

1) The choice of method(s) in all concertina repair in my view is firstly depending on IF there is a need/wish to preserve 'original' status of the instrument or not....i.e. whether there is some ambition of 'conservation' (or not...)

2) Some features in the original construction/design are NOT successful and the fixation of the thumbstraps is one of these. I would rather say it is pretty stupid from a technical viewpoint and anything done to improve it is motivated since there are great risks for much worse damage particularly with wooden ends if the arrangement is not working as it should....so:

 

add 1) IF you wish to fill out/strengthen the holes and put new wood-screws in I use a mush from twocomponent epoxiglue mixed with (if possible) the species of wood in the part to be mended. Very useful for ebony, mahoganny and so on... repairwork for instance since you want the same colour of the wooden parts too.

 

add 2) If the holes are too bad to get the small size screws in I always prefer using machine screws(bolts) with *as large a washer as possible* and a nut.

 

3) The long screws (or rather their sites...when damaged...) have caused a lot more trouble. With wooden ends you might reinforce the end from insided and skip the fixation to the post (not taking the post away since on push it protects the wooden end from cracking) and using wrist straps to reduce the risk for damage on pull.

I have thought of inserting a nut in the action board and using a long machine screw here also but you likely will have to make them yourself anyway..quite a bit of work. So I repair the actionboard hole with wood or the epoxi-mush and use the original screw again.

 

Goran Rahm

[Randy Hudson]

The epoxy mush was a clean, simple, and effective solution to my particular problem. I was surprised to find that on inspection, all four of the non-post screws were loose - so I used the mush on both screws on either side. Seems to have worked very well.

 

I performed this evening for the first time in a while with no fear that I might lose a thumb strap at any moment. Thanks to all.

 

Randy

[Chris Timson]

Paul - I actually hadn't felt your response inferred anything about my newbieness.  It just strikes me that it may be useful to be able to "upgrade" - anyone know if this can be done?

A fascinating discussion, particularly for people like me with seemingly more thumbs than usual. The only point I feel at all qualified on is this one. To get upgraded simply carry on as you are doing. Ranking is based on number of posts made. Once you get to 10 posts you become a "member", so not long to go.

 

I think I'll raise this in the suggestions forum, "newbie" is a term I also find at best clumsy and at worst condescending.

 

Chris

[Frank Edgley]

"The two shorter screws on one of my Englsih thumb strap have stripped. Any advice on best approach?"

 

Randy Hudson

 

Response: Sorry, I seem to have misread your original question. I guess being so immersed in anglos, and not reading your question carefully, I jumped to the wrong conclusion as to what you were asking.

[JimLucas]

For the purpose of filling those holes I have used what in America is known as "Plastic Wood" (that's a brand name). It's basically a wood-fibers-in-plastic-matrix product, where the plastic sets once exposed to the air. Easier than the suggestion to make something similar on your own. Some individuals have told me that it's too weak and doesn't work, but in that location I have found the strength to be more than adequate. At least it has held for more than 15 years in a couple of cases where I tried it, and it looks to hold for much longer still, though it would be little trouble even if it had to be redone annually.

 

I agree that bolts would be even better, at least if they don't have heads that stick up and poke into your thumb.

 

And Randy has already solved his own problem. Good work.

[d.elliott]

Plastic wood is something you buy, use half a milligramme from a 250 gramme pack, and in three or five years time you throw away the well spoiled balance.

 

An alternative, similar to Goran's idea, is to mix sawdust of the appropriate wood into PVA glue (White glue) to form a paste. Wet the surface of the hole/ damaged area with glue only, then quickly pack / trowel the hole with the glue & wood paste. Finally allow to harden, and away you go. Strong and effective, no waste.

 

Dave