Any ideas on how to fix this control cavity screw hole?

Discussion in 'Luthier's Corner' started by jk67SG, Aug 7, 2020.

  1. jk67SG

    jk67SG Member

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    Self explanatory... hole drilled too close to edge of cavity wall. My initial thoughts were to route out with forstner bit and glue piece of dowel in new hole, drill hole to receive screw in dowel (tearout of adjacent wood is a concern). Or, cut and drill new cavity cover, drill new hole closer to center of cover recess about 1/4" from original hole. Or cut a keystone shaped recess centered around original screw and cut a matching keystone shaped plug to fit recess, glue in place, drill hole for screw. Use original cover. SG Control Cavity Screw Tearout Closeup - IMG_2171.JPG SG Control Cavity Screw Tearout - IMG_2172.JPG
     
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  2. donepearce

    donepearce Well-Known Member

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    as it isn't cosmetically important, you could glue anther piece of wood alongside to thicken the wall at that point. You wouls need to cut away some of the shield to do it, but that is also unimportant.
     
  3. Von Trapp

    Von Trapp Well-Known Member

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    Admittedly I'm more of a toothpick guy but I think if you want a clean new hole then the forstner bit seems like the way to go. I'd clamp a piece of wood outside the screwhole, drill into both the guitar and that with slightly more than a semi circle in the guitar part, remove the wood piece, glue the dowel in and then chisel away the part of the dowel that extends into the cavity. Then drill a new hole for the screw. Obviously one would need a new cover then. Never done it so this is just the theory I'd work with...

    The easiest way by far is of course the one suggested above so it really depends on your preferences.
     
  4. jk67SG

    jk67SG Member

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    the toothpick trick isn't going to work here, because one wall of the hole is not solid, but basically wood fibers. Obviously the hole was drilled too close to the edge of the cavity and 53 years and swelling / contraction of the wood has takes it's toll.

    Great minds.... this was actually was very close to my first thought, like you, my idea was to cut a piece of wood to fit the curve of the cavity and clamp it in place to prevent tearout, use a Forstner bit to drill a hole with more than half of the hole in the recessed ledge, so that when the dowel was glued in place it would also be captive by the drilled hole. Essentially, the inner wall would bulge out slightly to shield and that would provide a solid place to anchor a screw. The problem with that is the controls and shield would have to be removed to accommodate the wood brace and clamp. I can't tell for sure, but it looks like the shield might be either glued or held by nitro, or both in the cavity, hence my idea to cut a keystone shaped plug that extended to the edge of the shield and carefully chisel or otherwise cut out a matching cavity to fit the plug. This is going to be one of those science experiment projects because there's no easy fix. Thanks for replying.
     
    Last edited: Aug 8, 2020
  5. jk67SG

    jk67SG Member

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    The problem with that approach is that the side of the screw hole wall next to the shield is not dimensionally stable... one side is broken open and what's left is not solid wood, but more like wood fiber. The easiest fix would be to have the control cover duplicated and drill a new hole about 1/3" away and slightly further from the cavity wall. Still spitballing ideas. I would like to keep everything as original as possible, it's 53 yo, so there's a historic factor involved too. Thanks for your reply.
     
  6. donepearce

    donepearce Well-Known Member

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    The extra piece of wood will stabilise it, and if you let the glue spread into the fibres, they will be stabilised too.
     
  7. Von Trapp

    Von Trapp Well-Known Member

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    From the pic it seems there 's some space between the shielding and the guitar. Would inserting something there perhaps do the trick, I mean, an operation where you don't remove the shield? I'm not good at measuring from pics so might be completely stupid so just a thought. What I'm thinking, if that's possible, is to "sand the guitar side with a small file, inserting a flat stick of sorts with some glue on it and then clamp it down over the shielding...
     
  8. AngelDeVille

    AngelDeVille Well-Known Member

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    Glue and a genuine tonewood toothpick.

    it’s just wood, not cardiac tissue
     
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  9. jk67SG

    jk67SG Member

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    I'm sorry for the poor quality of the photos. The problem is that it's not "just wood". It's wood on a little more than half of the hole, and crumbling bits of wood and wood fibers on the rest of the 'hole'. Toothpicks are fine if the hole isn't too big and the surrounding wood is structurally sound. That is not the case here.
     
  10. jk67SG

    jk67SG Member

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    To get a sense of the scale, a look at the wiring, or the insulators in the switch. The space between the shielding and the side of the cavity are roughly the thickness of a popsicle stick. It might be possible to file off any nitro off the wall if there is any and get down to clean wood... getting glue in there evenly also tricky but possible. And clamping would require a proper shim cut for the outside body of the guitar because the inside of the cavity and the outside of the body are no where near parallel. The hole would then need to be filled with something that is soft enough for the screw to make threads in it without being hard enough that the pressure of the screw going in wouldn't push that glued-in piece of wood away from the side of the cavity.
    Technically, I have skills to take all of the controls, switch and jack out along with the shielding. Historically the only way to date this guitar is a combination of the serial number and the pot date codes. Disturbing any of those things in the body cavity would bring into question their authenticity. That wouldn't make any difference to me if it were a re-issue, but in this case it's important.

    At this point it's looking like the best course of action would be to chisel and carve out a keystone-shaped cavity with a flat-ended X-Acto knife and cut a plug to fit it. Using a Forstner bit would require pulling the shielding or cutting away a big section so that a brace could be clamped in place to prevent tear-out, and that's a non-starter, or having a new control cover custom-made without a screw hole in that location and drilling a new hole in proximity to the old one where there is solid wood (retaining the old cover for historic reasons), or just leaving it the way it is without the screw installed.

    Thanks everybody for your inputs and spit-balling this with me.
     
  11. AngelDeVille

    AngelDeVille Well-Known Member

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    hence the glue
     
  12. DrBGood

    DrBGood Well-Known Member

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    I'd drill this out, glue in a dowel and voilà.

    .jpg
     
    Last edited: Aug 9, 2020
  13. Von Trapp

    Von Trapp Well-Known Member

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    Right, well like I said, not good a judging from pics. It's a tough nut I guess, especially when you don't have the guitar in front of you. I don't have good experience myself from xcacto knives, I've found them too brittle. A sharp chisel always works but uncertain if they exist that small but I'm not sure I'd be able to make the bottom flat enough.

    I'm still for the drill as best option. I'm starting to think that the popsicle stick, toothpics, glue and a regular drillbit are is the way to go. But then again, sometimes my lateral thinking carries me away a bit too far...

    However, perhaps you should check if the control shield really can't come off? I have no idea but it does sound strange that it would be glued in there. More likely then that it's just just stick to nitro and if so it should come off with some wiggling.
     
  14. cerebral gasket

    cerebral gasket Well-Known Member

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    I remember those old vintage cavities with the shielding. They got smart years later and added bump outs so that wouldn't happen. I had to plug and re-pilot two holes on my 2006 SG Classic because they couldn't be bothered to line them up with the holes on the cover plate at the factory. Screws were jammed in at an angle.

    [​IMG]

    I would use toothpicks as others suggested. If toothpicks too small in diameter, use either wooden cotton swabs or bamboo skewers.

    [​IMG]

    Glue is stronger than wood.
    With hole close to edge, clamp it.
    Once dry, will be golden.
     
  15. jk67SG

    jk67SG Member

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    @Von Trapp:

    Drilling with a normal bit is problematic because the bit will try to follow the original hole. The only way to do this successfully would be to use a drill press and to clamp the guitar body to the drill press table, which is problematic, as you can imagine, because of the bridge, trem, pickups, control knobs and pickup switch on the side that would face the table.
    The kind of X-Acto knife I'm talking about is a heavy duty one, not the smaller kind that normally comes to mind for use by hobbyists. It would be slow, tedious work, working down a thin layer at a time, and the bottom doesn't necessarily have to be perfectly flat, as the vertical sides would orient the plug.

    I'm resistant to removing the shield and controls from the cavity for the aforementioned historical dating reasons.
     
  16. jk67SG

    jk67SG Member

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    Thank you for your suggestion.
     
  17. cerebral gasket

    cerebral gasket Well-Known Member

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    No drill press.
    Plug the hole with toothpick and glue.
    Use pin vise to pilot new hole.

    Keep it simple.

    [​IMG]
     
    Last edited: Aug 9, 2020
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  18. donepearce

    donepearce Well-Known Member

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    Dowels - I am very much in favour of using a dowel to make a tidy job, but ONLY where it will be supported all the way round. In this case it will be hanging out in the air on one side, and if you try to put a screw into it, the grain will simply open up and it will fail. You need a piece of wood that has the grain running in the appropriate direction, which is roughly the same as the wood of the body. Get a decent sized chunk and glue it alongside the hole. Fill the hole with wood slivers and glue. Once it has all dried, drill a new pilot hole and the screw will hold nicely.
     
  19. jk67SG

    jk67SG Member

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    donespearce said "You wouls need to cut away some of the shield to do it, but that is also unimportant."

    If this was a re-issue I would have no problem doing this. But, while it's not a '59 Les Paul, it does have some historic value, and it's it pretty good condition after 53 years. Any repair will have to be done without inflicting new damage.

    I would rather leave the screw out than cut away a section of the shield.
     
  20. donepearce

    donepearce Well-Known Member

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    I get that. So don't cut the shield, just bend it way from the wall far enough to get the support piece in there. It's quite flexible.
     

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