Neck reinforcement merbau

Construction and repair of Classical Guitar and related instruments
Mikefm
Posts: 14
Joined: Mon May 20, 2019 4:20 am

Neck reinforcement merbau

Post by Mikefm » Tue Sep 10, 2019 11:44 pm

I am wondering if anyone has used merbau as a wood for reinforcing a neck. An elderly classical guitar I have is gradually becoming unplayable due to the neck bowing upward. Rather than tackle the daunting process of removing the fingerboard I would like to rout a slot in the back of the neck and fit a merbau strip around 12mm deep, 9mm wide, finishing flush. Carbon fibre is difficult to source locally, and expensive. The neck can be coaxed back to straight using a jig and clamp, and will stay that way for a while, but gradually creeps forward again. I am hoping to counteract the bow by glueing in a strip while the neck is in a straight position.

I've tested several timbers, Red gum, Tassie oak, and Merbau, making strips and testing their relative strengths by simple bending. Merbau is the stiffest, just ahead of red gum, in keeping with the figures for elastic modulus posted on the Wood Database. Ebony is available online, in the form of fingerboards, but it is unclear how they have been sawn. I suspect the grain direction of quarter-sawn timber would not be the best for this application.

Any advice would be much appreciated.
Rodes ca. 1972
Mitsuru Tamura mod.3000 1979
Manuel Contreras 1a 1986

bftobin
Posts: 88
Joined: Sun Feb 12, 2017 11:02 pm
Location: Canada

Re: Neck reinforcement merbau

Post by bftobin » Wed Sep 11, 2019 4:10 pm

Before 'major surgery' I would try putting a hot clothes iron (no steam) to soften the glue and then into
the jig overnight. It works quite well most of the times I've tried it. The technique was shown it a book
I bought back in the 1970's 'Complete Guitar Repair' by a Japanese gentleman in California, I can't
remember his name at the moment.

Brent

MessyTendon
Amateur luthier
Posts: 2050
Joined: Fri Jun 19, 2015 1:33 am

Re: Neck reinforcement merbau

Post by MessyTendon » Wed Sep 11, 2019 6:17 pm

Removing the fingerboard and installing the rod would be the proper way to do it. If you do it the other way around you will have trouble dealing with the curved part of the neck and it will require further scraping to make the rod flush, which would change the neck profile.

You have more room for error removing the fingerboard...another advantage to doing it by fingerboard removal is you can then figure out if it will even work...if it doesn't correct the issue then you can always put the fingerboard back, but it also leaves the better option of stiffening things further with a new fingerboard of greater strength, and thickness.

Plus stainless frets...go all in. That's just so much work either way. Go for the gusto. Another absurd option which can work is clamping it down with an electric blanket...the heat can do the job...heat it...let it sit...turn off the heat, and repeat. It just might spring back...I agree it's a good option to try the least difficult option.

A rod insert is major surgery, and I feel it's best to go full rebuild even if it's overkill because in the end it will be better than it was new.

Marshall Dixon
Posts: 817
Joined: Fri May 15, 2015 5:06 pm
Location: SW Oregon

Re: Neck reinforcement merbau

Post by Marshall Dixon » Wed Sep 11, 2019 8:49 pm

bftobin wrote:
Wed Sep 11, 2019 4:10 pm
Before 'major surgery' I would try putting a hot clothes iron (no steam) to soften the glue and then into
the jig overnight. It works quite well most of the times I've tried it. The technique was shown it a book
I bought back in the 1970's 'Complete Guitar Repair' by a Japanese gentleman in California, I can't
remember his name at the moment.

Brent
The author you refer to is Hideo Kamimoto. I haven't tried it but it seems like it would be a good place to start.

Fret wire comes with different tang thicknesses and a snug fit in the fret slot will help prevent bowing.

Some will also put glue in the fret slot when inserting frets. I've most commonly read of epoxy being used for this, but also HHG and CA glues.

Mikefm
Posts: 14
Joined: Mon May 20, 2019 4:20 am

Re: Neck reinforcement merbau

Post by Mikefm » Thu Sep 12, 2019 11:46 pm

Thank you all for your good advice. I must say I'd prefer any option that does not involve surgery, and the recommendations above imply that too. You mentioned, Brent, the heat treatment, and it looks the best option to go with. A long period of just "cold bending" has had a beneficial effect, but I am sure with heat the results will be longer lasting. Not knowing much about the behaviour of glue when heated I followed up Marshall's lead and found the information published by Hideo Kamimoto, and was surprised to find his placement of clamps and jig was very close to what I have done. Going further I found good information on the effect of heat on Titebond 1 compared to hide glue, in "frets.com"

Aliphatic resin gives me the creeps!
Heat Testing Glue Joints
© Frank Ford, 4/25/98; Photos by FF, 1997

So there is no doubt that heat softens glue, to the point of complete failure, but I wonder if it regains its strength and adherence qualities when cooled. I assume it does, or I doubt the process would have been described as a cure for a bowed neck. I will proceed with cautious heating.

Thank you once again, gentlemen, for guiding me toward the best solution. I am indebted to you, and the Delcamp forum this excellent advice.
Rodes ca. 1972
Mitsuru Tamura mod.3000 1979
Manuel Contreras 1a 1986

Marshall Dixon
Posts: 817
Joined: Fri May 15, 2015 5:06 pm
Location: SW Oregon

Re: Neck reinforcement merbau

Post by Marshall Dixon » Fri Sep 13, 2019 12:59 am

Mikefm wrote:
Thu Sep 12, 2019 11:46 pm
...
Thank you once again, gentlemen, for guiding me toward the best solution. I am indebted to you, and the Delcamp forum this excellent advice.
Isn't this a great forum? Here we can pick the brains of world class luthiers, teachers, players, composers, artists, computer experts... and moderators. This can't be an easy job running this web site.

Something I thought of since posting last: a podcast called Classical Guitar Insider hosted by Brent Williams. One episode (several years ago) featured Aaron Green, a luthier that posts on this forum. I recall him talking of having the neck of a prized guitar straightened by using heat. I don't recall any of the specifics involved about the process.

Here is the podcast. The relevent conversation starts around 19:00. (It was a Fleta.) :

http://classicalguitarinsider.libsyn.co ... aron-green

Mikefm
Posts: 14
Joined: Mon May 20, 2019 4:20 am

Re: Neck reinforcement merbau

Post by Mikefm » Fri Sep 13, 2019 4:44 am

You can include yourself, Marshall, as one of those great resources inhabiting the Delcamp forum. The comments in the replies above comments started a sequence of valuable discoveries for me and will no doubt lead to a successful solution. I heartily agree with your sentiments regarding the forum, and I am always amazed by the generosity of the members in giving time and thought for the benefit of so many. There's a camaraderie shared by guitarists here that allows even the most lowly, such as myself, to share in the wisdom of those whose experience and abilities far exceed their own, somewhat reminiscent of the Guild Halls of medieval Europe, where the masters were always approachable by the apprentices for enlightenment and instruction.

Thank you for the link to Aaron Green's comments. I appreciate your taking the time to consider the problem for me and come up with even more gems of information.

The guitar in question I bought new in 1972. Slightly larger than a Ramirez 1a it has a wonderfully robust and balanced sound, making it well worth any time or effort involved in correcting the problem. With a straight neck it plays so easily, the action quite comfortable even for my aging hands, while my more expensive instruments tire me more quickly.

Kind regards, and thanks again,

Mike.
Rodes ca. 1972
Mitsuru Tamura mod.3000 1979
Manuel Contreras 1a 1986

Mikefm
Posts: 14
Joined: Mon May 20, 2019 4:20 am

Re: Neck reinforcement merbau

Post by Mikefm » Sat Sep 14, 2019 12:18 am

Thanks to the helpful comments from the kind gentlemen who responded, I have followed up the principles of wood bending and the influence of heat. A well-researched description of the chemical and physical changes that occur in wood as it is heated was posted by Joe Scharle in the North Carolina Woodworker forum. Here are a few lines in which he summarises the effects of heat relevant to my inquiry, and perhaps for others who are interested in what happens to wood when heated:
" All of this data shows that under heat and pressure, the lignin-hemicellulose matrix becomes thermoplastic and will deform to a different stable matrix. If the compressed matrix is cooled under pressure, the newly formed matrix has little memory of its precompressed form."
It seems to me then, that heating the glue between the fingerboard and the neck is not necessarily a good thing if it reduces the integrity of the bond, but that if the wood is heated to around 100C for an an hour or so the lignin in the wood can be permanently restructured, hopefully without exceeding the limits of the glue bond. The wood (neck) needs to be fixed in place while cooling, as described by Hideo Kamimoto and others.
The best solution is just as you chaps have described. Thank you once again!
Rodes ca. 1972
Mitsuru Tamura mod.3000 1979
Manuel Contreras 1a 1986

Return to “Luthiers”