Repairing screw holes in a guitar neck...

[rwillett]

Hi,

 

I'm trying to reuse this Yamaha guitar neck on a 3D printed guitar. See below if you have interest in following my fumblings as I grope in the darkness to completion

 

 

The current screw holes look slightly tatty, epsecially the two towards the tuners end of the neck. The heal screw holes look OK.

 

I've been reading (or doing my own research as the flat earthers would say) about what to do. The general gist seems to be fill the tatty holes with the same material and wood glue. So hammer in small toothpick bits of maple and let it dry and then drill new screw holes. The neck appears to be maple

 

according to https://www.axebition.com/electric-guitar/yamaha-rgx-121dm

 

Somewhat surprisingly I don't have any maple dowels or offcuts lying around, PLA and PETG filament, yes, maple, no.

 

So the question I have do I need maple or could I just use toothpicks and woodglue here?

 

I do recall reading on here that people create dowel plugs that match the direction of the grain, is this necessary for this?

 

Lots of questions and sadly not a clue from me

Any help or advice welcomed.

 

many thanks

Rob

[Geek99]

Use furniture dowels - who will see the grain there ?

Edited November 2, 2023 by Geek99

[SamIAm]

One approach would be to use bolts/inserts instead of screws; nice and solid and no need to fiddle with glue etc.

https://nectite.com/

 

I've seen one of the builders here on BC mention using them ... but I can't recall who!

edit: found it!

 

S'manth x

Edited November 2, 2023 by Smanth

[tauzero]

I've used inserts and bolts along with ferrules rather than a neckplate: https://graingerguitarparts.com/t/neck-ferrules--screws

[sandy_r]

55 minutes ago, Geek99 said:

Use furniture dowels - who will see the grain there ?

 

...although you'd want to match grain direction (and close match to wood type) to fill visible holes for 'cosmetic' reasons, i believe that the reasons for doing so when you just wish to redrill are to do with making the wood in the filled hole more 'homogenous' with the original surrounding material, so that the drill, and subsequent screw, cut through the wood with minimum divergence from the intended path

 

i think that its probably more important that the wood you use to fill the holes is a closer match to the density and nature of the maple, than the colour/ grain effect.  Personally, i'd source an offcut of something suitable and chisel a few thin dowels, very slightly oversize at the protruding end, and then woodglue & mallet them in. finish off with a clean chisel cut across the protruding 'dowel', to enable a good start to the drilling of the  new hole

 

...i used to know this stuff, but now i understand that my 'grey matter' contains a lot of unfilled holes...

 

Edited November 2, 2023 by sandy_r

[rwillett]

48 minutes ago, Geek99 said:

Use furniture dowels - who will see the grain there ?

I thought the reason that the grain direction in the dowel to match the grain direction in the neck was due to strength, but that could be wrong.

 

Rob

[rwillett]

48 minutes ago, Smanth said:

One approach would be to use bolts/inserts instead of screws; nice and solid and no need to fiddle with glue etc.

https://nectite.com/

 

I've seen one of the builders here on BC mention using them ... but I can't recall who!

edit: found it!

 

S'manth x

 

Thats a good idea, if I put the bolts through neck ferrules, then it spreads the load across the plywood back plane.

[rwillett]

6 minutes ago, sandy_r said:

 

...although you'd want to match grain direction (and close match to wood type) to fill visible holes for 'cosmetic' reasons, i believe that the reasons for doing so when you just wish to redrill are to do with making the wood in the filled hole more 'homogenous' with the original surrounding material, so that the drill, and subsequent screw, cut through the wood with minimum divergence from the intended path

 

i think that its probably more important that the wood you use to fill the holes is a closer match to the density and nature of the maple, than the colour/ grain effect.  Personally, i'd source an offcut of something suitable and chisel a few thin dowels, very slightly oversize and mallet them in. finish off with a clean chisel cut across the protruding 'dowel', to enable a good start to the drilling of the  new hole

 

...i used to know this stuff, but now i understand that my 'grey matter' contains a lot of unfilled holes...

 

 

That sounds similar to what I read about the grain direction. Its not just cosmetic.

 

I think the inserts are an easy fix. Other people seem to sell them as well, so it does appear to be a genuine solution https://graingerguitarparts.com/t/neck-ferrules--screws

 

Thanks

Rob

[rmorris]

I'll stick my neck out (see what I did there 😊) and suggest that in reality it makes no significant sonic difference. Just wood glue a cocktail stick or two in there, leave it to dry for some days regardless of what it says on the tube etc. Finish it flush, and rescrew. Although if planning to remove / refit neck often then inserts may be a good choice. 

Note that machine screws/threads come in loose / medium / tight grades wrt thread fit. The default is medium. I suggest just giving the screwba tiny extra bit of force into the thread. Recommend hex or torx screw heads. North American people may wish to look at those "square" bit drivers.

In general they seem not to be a thing in Europe ? 

And, of course, we should all be sticking to metric units now 🙂

[sandy_r]

1 hour ago, rmorris said:

I'll ... suggest that in reality it makes no significant sonic difference. Just wood glue a cocktail stick or two in there, leave it to dry for some days .... Finish it flush, and rescrew. ...

 

Using a suitable type of wood, and aligning the grain, to fill a hole for redrilling has nothing to do with "sonic difference", and everything to do with ensuring that the new drilling and screw fitting process goes smoothly, and is as close to achieving the same accuracy and stability of the drill and screw action as with the original work (this is especially important to accurately and securely locate something as technically demanding as these two parts under great string tension)

 

Edited November 2, 2023 by sandy_r

[lemmywinks]

I had a broken screw removed and some scruffy neck holes repaired by a local guy, he made maple dowels with the grain in the correct position. You can probably buy suitable dowels online or use a plug cutter bit to make some.

 

Tuners you can get away with cocktail sticks or matches but I'm not sure I'd want to risk it with neck bolts.

[PaulThePlug]

Ikea near you?.. wood dowls in the fittings boxes...

[rwillett]

Nearest IKEA is Warrington  or Leeds. Each are nearly two hours each way. 

 

I can order stuff online so that's not an issue. 

 

To be honest I think I'll go with the bolts and inserts.  That's an easy fix and doesn't require me to work out grain direction and avoids glue. I suspect if I use glue, I'll need to be cut out by the Fire Brigade. 

[rwillett]

I've ordered some m5 countersunk bolts, some m5 threaded inserts and solid cup washers. £20 for 20 sets so cheaper per set than the 'dedicated' stuff. 

[rmorris]

22 hours ago, sandy_r said:

 

Using a suitable type of wood, and aligning the grain, to fill a hole for redrilling has nothing to do with "sonic difference", and everything to do with ensuring that the new drilling and screw fitting process goes smoothly, and is as close to achieving the same accuracy and stability of the drill and screw action as with the original work (this is especially important to accurately and securely locate something as technically demanding as these two parts under great string tension)

 

 

Overthinking it tbh. The dimensions involved make grain orientation insignificant. Really you just need enough added material for the screws to properly bite enough esp wrt the, as you say high tension. I do like the idea of the threaded inserts/ machine screws though. I can see arguments against wrt thread / fit tolerance etc. But I say that is taken care of by the aforementioned high tension from the strings.

Edited November 3, 2023 by rmorris
typo

[sandy_r]

9 hours ago, rmorris said:

Really you just need enough added material for the screws to properly bite enough

 

No - really - using cocktail sticks to fudge the repair of a hole requiring accurate locating of drill and screw highlights the difference why some people became luthiers and others, such as you and i, were just 'working as a waitress in a cocktail bar' 😉

 

(no-one is disputing the merits of using threaded inserts)

 

[Andyjr1515]

Just to clarify why screws inserted into end grain give a weaker joint weaker than screwed into cross grain, it is all about that in pretty much all timbers the fibres themselves are very strong, but the bond between all of the fibres is relatively weak.  Think about splitting wood for a fire - a wedge sitting on the end grain and hit with a hammer will split the log easily.  But turn the log round and sit the wedge on the side to try to cut through the fibres themselves...the hammer will just bounce off.

 

And this is what the force of a tightening screw will do.  If the plug has the fibres along its length, then this is what the screw threads are doing once the joint is secure and you start tightening the screw fully:

 

The fibres are running vertically and the upward force from the thread faces will split the bond between the fibres at the dotted line shown all around the screw.  If you keep turning the screw, it will simply pull all of the wood trapped in the threads out

 

If the fibres are running horizontally, then the upward force from the thread faces is now having to try to break the strong fibres themselves, not the weak bond between them:

 

In this view above, yes, some of those fibres are split by the thread. 

 

But if we look end on what those fibres are doing around the screw...

  

Uncut fibres, now seen end on. are completely surrounding the thread.  And under normal screw tension, they simply will not fail.

 

So:

- If you are going to plug, then use a cross-grain plug, preferably larger than the screw thread outside diameter you are going to use, re-drill your pilot hole and use the screw to cut its new thread

 

- An insert will be going into the original cross-grain wood and so is already going into cross grain wood.  And the insert has a wider thread, spreading the forces over a wider area, which is also a good thing.  As such, that is also a good solution 

 

 

Edited November 5, 2023 by Andyjr1515

[rwillett]

@Andyjr1515

 

Thank you for the comprehensive description. Thats a great explanation of why cross grain wood plugs are important for load bearing. I also know that there is a website dedicated to wood plugs, https://plugitwood.co.uk/ I suspect the wood is rather important in Google Search here

 

I've just inspected the end of the neck again, and what appeared to be a right mess for the top two holes, aren't as bad as I thought. There's only a mmm or two of damage. It looked worse than I thought.

 

So my plans are:

 

1.  I will try normal guitar neck screws, preferably with a ferrule to spread the load. Failing that ....

2. .. I'll move to threaded inserts, which I think I can do.  Failing that (and by this time I expect to have lost a finger or two) ....

3. .. I'll buy some end grain plugs from the website above and try and glue them in and move back to stage 1.

4. .. Give up.

[Andyjr1515]

53 minutes ago, rwillett said:

@Andyjr1515

 

Thank you for the comprehensive description. Thats a great explanation of why cross grain wood plugs are important for load bearing. I also know that there is a website dedicated to wood plugs, https://plugitwood.co.uk/ I suspect the wood is rather important in Google Search here

 

I've just inspected the end of the neck again, and what appeared to be a right mess for the top two holes, aren't as bad as I thought. There's only a mmm or two of damage. It looked worse than I thought.

 

So my plans are:

 

1.  I will try normal guitar neck screws, preferably with a ferrule to spread the load. Failing that ....

2. .. I'll move to threaded inserts, which I think I can do.  Failing that (and by this time I expect to have lost a finger or two) ....

3. .. I'll buy some end grain plugs from the website above and try and glue them in and move back to stage 1.

4. .. Give up.

Sounds like a good plan