Heel Block gluing abnormality ?

[donnyb]

Hello,
I am in the process of doing a neck reset on a 1970 Suzuki 12 string. I have the neck off and the dovetail joint sanding close to completion.

I have just noticed that there is an air gap under the entire width of the neck heel block, where it meets the back of the body. On measuring the gap, it is on average .030" wide and extends back about 30mm.

There appears to have never been any glue under there. None is obvious anyway and a feeler gauge slides back under the heel unobstructed. However there is plenty of glue squeeze out on the adjacent kerfing.

https://imgur.com/0dTMZmU


So my question ....Do neck heel blocks always get glued to the body back ?

regards,
Donnyb

[mirwa]

Well I do.

In your photo, I think its just glue failure.

Some builders like to have as much of the top and back un-attached as possible, its not unusual to see neck and back blocks taper away from the kerfing

Steve

[charles Tauber]

As Steve said, it might just be glue failure.

It is difficult to say from the photo, but it is possible - conjecture - that the block was hung-up on the centre reinforcement strip: the strip was too long and the block couldn't contact the back.

The shadow on the centre strip suggests that the strip is lifting near the back brace.

It is usual to glue the block to the back for the entire footprint of the block.

[donnyb]

Originally Posted by mirwa

Well I do.

In your photo, I think its just glue failure.

Some builders like to have as much of the top and back un-attached as possible, its not unusual to see neck and back blocks taper away from the kerfing

Steve

Thanks Steve. I thought surely it should be glued !

[donnyb]

Thanks Charles too. I think you're on the money with the cause of it.

Now, should I fix it by injecting epoxy under there ? Or is there a standard fix for this ?

[mirwa]

30 thou wide is not going to pull up nicely without a buckle in the back happening, so that rules out using a conventional glue like hide/titebond etc,

I would epoxy pour the gap, run some tape along each side of the block, stand it upright and inject the epoxy in place using a syringe. This will give some glue strength to the joint and not distort the back

[donnyb]

Originally Posted by mirwa

30 thou wide is not going to pull up nicely without a buckle in the back happening, so that rules out using a conventional glue like hide/titebond etc,

I would epoxy pour the gap, run some tape along each side of the block, stand it upright and inject the epoxy in place using a syringe. This will give some glue strength to the joint and not distort the back

Yes that fix would be best I think Steve.

I just tried light pressure clamping of the back to the block and although the gap did compress a little, maybe down to .015", its had a long time in that condition and would have that memory permanently in it I think. Seems epoxy acting as a filler but with adhesion as well would work best as you say.

Maybe this contributed to the neck absolutely needing a reset as others had tried the usual saddle and bridge shaving 'fixes'. Guitar is 50 years old too.

[donnyb]

Hmm. Should I finish the neck reset i.e. glue the neck back on etc, and then do the block gap epoxy job, or the other way round ? As I will be using my neck clamping jig which will exert a fair bit of pressure on the heel and surrounds.

[Taylor Ham]

Originally Posted by donnyb

Hmm. Should I finish the neck reset i.e. glue the neck back on etc, and then do the block gap epoxy job, or the other way round ? As I will be using my neck clamping jig which will exert a fair bit of pressure on the heel and surrounds.

I think the body should be stabilizied before re fitting the neck.

[donnyb]

Thanks Taylor.
Stabilizing the body first makes sense, given the very small amounts of wood I'll be removing from now on from the heel for the desired final reset angle.

In doing that final heel sanding, I'll also be stringing it up a few times in a certain manner in the neck clamp jig to approximately 200lbf to simulate the force of 12 strings at pitch to check bridge to neck projection.

So again, body through stability in the neck block first makes good sense. Thanks again.

[redir]

I don't think I would worry about that. I've seen guitars of that era and much older that have that and it was probably that way from the day it was manufactured and it never caused any problems. If you are hell bent on fixing it then a paper thin shim of wood fitted and glued in there would be best me thinks.

[donnyb]

Even better Redir. And its not hard to do that fitting. I have paper thin maple shims for other purposes already.

Do you think though that it was intentional at manufacture ?

[John Arnold]

I would insert a slice of wood in the gap, glued with Titebond or hot hide glue. The structural concern of doing nothing is the block could separate from the back, allowing the block to shift. That will cause the neck to pitch up, increasing the neck angle and defeating the reset.
This was one of the first repairs I ever did on a quality guitar, nearly 50 years ago. The neck block shifted along with the sides, leaving a gap at the binding. It was my older sister's 1952 Gibson LG-3, which she still owns.

[donnyb]

Thanks John. Thats what I will be doing and I have very thin maple shims on hand (somewhere!).

This block condition either from new or from age ( the block separation is as wide as the block, at least extending 30mm back under) might have contributed to the guitar becoming unplayable due to unusually large string clearance over the fretboard even for its age. But then , it is a 12 string and not top of the range at the time.

[John Arnold]

Any shifting of the block would show visible separation of the back binding.