best wood for neck dovetail shims?

[Brian Evans]

I have a 1946 Epiphone Zephyr archtop that needed a neck reset - the cheeks of the dovetail were pulling away from the sides, and the neck was visibly rotating.  Local luthier did the job, and it failed after around 6 months.  Same luthier redid the job (for free) and it failed again.  He has washed his hands of it, and I wouldn't trust him for a third try anyway.  He said this:  "I used yellow AR glue and ebony shims".

I build archtops and I'm not a repair technician (which I frankly think is a whole step and a half harder than building) but I am going to have to tackle this neck reset in the next few months.  I am going into a jig building mode, and I'll build a neck press, etc.  I have no doubt that once I get the neck off I can follow through with the reset.  I'll use hot hide glue, clean out old glue, all of that.  My questions are:  Is my instinct that using AR glue and ebony shims was a fundamental mistake correct?  The brand of glue (Lepage Pro Carpenter) even says to de-grease oily wood before gluing, and I feel that ebony qualifies as oily, and he didn't degrease (I asked).  And what is the correct wood to use for shims?  Fairly certain the neck is maple, no idea about neck block.  My sincere hope is that the previous repairs didn't crack the neck block...

Thanks, Brian

[Roger Häggström]

Looks like its a pretty standard dovetail, with any shim and glue the neck should stay in place if the fitting is OK. Hide glue and maple shims are great choices. Maple is hard enough and pretty easy to shape and the same wood as in the neck. Any wood will do for a shim except really soft wood like spruce, the bulk of the job is done by the locking of the dovetail.

I suspect you are right about the neck block, maybe it's cracked or not glued to the top or bottom. Something isn't right anyway, the neck should not be able to move with fresh glue and a good enough fit.

[Christopher Parker]

Yeah - ebony is oily, and wouldn't be my choice for dovetail shims, but if the joint is tight, it shouldn't matter, right? I've used AR to glue on countless ebony bridges, and I've yet to ever see one that I glued on pull up. A properly fitted dovetail wouldn't be subjected to nearly as much stress. I don't think the choice of glue or shim material is to blame.

In what way did it fail? It's possible that the neck block has cracked or has come loose from the top, sides, or back.

[Brian Evans]

All three failures were the same symptom (which is not to say the same cause, I know).  The first one, on the 70 odd year old original joint, was the neck rotating out of the dovetail mortise creating a gap at the bottom that you could see light through side to side.  These guitars have a funny compression truss rod, which adjuster extends from the neck under the floating fretboard extension towards the bridge.  The truss rod adjuster eventually tipped down to almost touching the top, which is why I decided to have the neck reset the first time.  The second and third failures were essentially the same thing, a visible gap at the bottom and the joint rotating out of the head block mortise.  We discussed headblock failure, other joint failure as you suggest, but he said there was no signs of such, so I had to trust him.

[Ian Pender]

I've seen someone recommend using Holly veneer for neck shims, since it apparently compresses quite a bit, allowing you to get a tight fit more easily. Keeping that in mind, I'd never use ebony for this purpose, since it's so hard. Personally, I've always used maple veneer and hide glue. Based on what you've described though, I'm guessing that the guy who reset the neck just didn't get a good fit before gluing.

[onewent]

Yes, I've been using holly shims for a number of years for that reason with success.  iirc, this is what Martin used?  ..memory fades...

The only dt I've had fail was on our pastor's 12-string (which I reset gratis).  The heel had pulled out again after a few years, and once I wiggled the neck off again, I saw that the cause was the end block had split, and the glue joint was still pretty solid.  This guitar is a pacific rim-made budget 12-string, so not the greatest of materials.

[Ian Pender]

I have a cheap Stella guitar that I reset the neck on that had a split block and side. Here's a before photo, the thing was pretty trashed. Definitely not worth the work I put into it, but I did it years ago as a learning experience. It's still holding up, and it's actually kind of a fun guitar to play now that it's set up proper.

[Howard Klepper]

Ebony is not all that oily and there is no reason AR glue shouldn't stick more than well enough to it.  But it's a weird choice for a dovetail shim, and makes the tech's work suspect.  Any medium weight wood will do:  maple, mahogany, cherry, walnut, sapele, whatever.

[Frank Ford]

aking apart original Martin joints can reveal any number of shims.  Mostly, I've seen maple veneer, but sometimes thin fiber, and even paper shims.  

Considering that the joint is basically under compression, I figure that most anything would make good shim material, so I've often used snips of business cards as well as thin veneer strips.  While it's not a bad exercise in craftsmanship to glue shims to the dovetail and chalk-fit the joint to perfection, it's hardly necessary.  

As to the glue sticking to shim material, well, since the joint is self-locking and basically can hold the load with no glue at all, I wouldn't spend much time de-greasing or worrying about that.