Neck strength and size HELP?

[justrythym]

Good morning Gentleman. I need some guidance here. My question is this....... the mandolin I have been working on had a very large neck. My Son is used to a smaller neck profile. I rasped the neck down to a more suitable size. I hope I did not go to far. The neck thickness close to the first fret is 20mm including the fretboard, thicker at the nut. But the neck has a fairly sharp V, so not as much meat on the sides. The fretboard measures about .180 thickness and has been fretted but not glued on yet.

The neck no longer has a truss rod, I put a stiffener from some ironwood I had here and epoxied in.

1. Is there any adhesive I can use that would add strength? Not worried about removal.

2. Should I be concerned about the string tension on this mandolin? I would like your opinion based on the description. Thanks, Gentleman

[fscotte]

Rout out the ironwood and replace it with carbon fiber rod. I use a 1/2" tall x 1/4" wide the full length of the neck into the headstock.

It wont move.

[Richard500]

Non-builder here. 20mm-0.180” is 0.607”. I just miked my small collection of bowlbacks, and you’re very comparable. These have no reinforcement[and have been holding tension for an average of a century. Remember that most of the strength of a beam is it’s web, that is, the 0.607 dimension, not the width, so barring magical knowledge of the particular piece of wood you have, you are likely still in range. As for fingerboard glue, it depends on the wood species, but I think epoxy is going to be strong, but this also may have no effect on the neck’s resistance to bending unless you use a glue that can creep. I’m sure luthiers do not like unn-removable fingerboards. The people here tend to recommend light or extra-light strings on suspect structures —- like bowlbacks, and of course lowest usable string height helps.

[justrythym]

Non-builder here. 20mm-0.180” is 0.607”. I just miked my small collection of bowlbacks, and you’re very comparable. These have no reinforcement[and have been holding tension for an average of a century. Remember that most of the strength of a beam is it’s web, that is, the 0.607 dimension, not the width, so barring magical knowledge of the particular piece of wood you have, you are likely still in range. As for fingerboard glue, it depends on the wood species, but I think epoxy is going to be strong, but this also may have no effect on the neck’s resistance to bending unless you use a glue that can creep. I’m sure luthiers do not like unn-removable fingerboards. The people here tend to recommend light or extra-light strings on suspect structures —- like bowlbacks, and of course lowest usable string height helps.

Thanks much appreciated! Was hoping RCC56 would chime in here as well.

[pops1]

Use epoxy for the carbon fiber rod, not for the fingerboard.

[justrythym]

Use epoxy for the carbon fiber rod, not for the fingerboard.

What is the downside to epoxy other than removal?

[fscotte]

The downside is there’s no reason to use it on fingerboard. It works well for the carbon fiber, but that’s all I’d use it for.

White glue is fine on fingerboard.

[justrythym]

The downside is there’s no reason to use it on fingerboard. It works well for the carbon fiber, but that’s all I’d use it for.

White glue is fine on fingerboard.

Im absolutely a novice. But it seems to me that if one cared nothing about removing the fretboard. Wouldnt using an adhesive that has less chance of creeping add stability to the whole neck. Correct me if I am wrong. Thx. JR

[rcc56]

The neck will probably be ok if it is reinforced.

Carbon fiber is popular for reinforcements these days. I recommend recessing it a couple of millimeters beneath the gluing surface of the neck and covering it with a hardwood strip, because carbon fiber doesn't like to be sanded, filed, or planed level. The preferred glue for laying in a carbon reinforcement is epoxy. I've only used carbon fiber for reinforcement once, and it worked very well.

In the old days, hardwood reinforcements were fairly common. Many have held up very well. The million dollar question on a hardwood reinforcement is finding a piece that's stiff enough to hold up for the long term. Martin's T-bar worked well also, but I wonder if a mandolin neck might be too small for a T-bar to be practical.

I've seen quite a few warped necks on Martin guitars with the later hollow square bar, but I suspect the use of white glue was more at fault than the bar. In the old days, I might have considered a solid square steel bar for a mandolin neck reinforcement, but carbon fiber is much lighter.

I am a proponent of hot hide glue for neck to fingerboard joints. It's one of the joints that you really don't want to creep under any circumstances.
If you're not comfortable with using hot hide glue, my next choice is Titebond Original.

It's the same old song over and over again. I use these glues for most wood to wood joints in fretted instrument repair because they have proven themselves very well over many years.

As a repairman, I don't like white glues. If a joint has to be redone later, it's really hard to get rid of the old white glue to ensure the new joint will hold. And I have seen too much creeping on too many joints on too many Martin guitars assembled with white glue.

Glue in itself does not make wood stronger. But the technique of lamination can stiffen a neck, depending on the woods used, the orientation of the grain, and the type of glue. For lamination to be most effective over a long term, the cured glue should have very low elasticity. A fingerboard to neck joint is a type of lamination.

There is a banjo maker who insists on using epoxy for fingerboards. He is of the opinion that any water based glue encourages warping or cupping of the wood. He also believes that it would be easy to break an epoxy joint with heat should an instrument need repair. I heartily disagree, and if one of his instruments comes to my shop, I will ask the owner to instead send it back to the maker for the repair.

[justrythym]

The neck will probably be ok if it is reinforced.

Carbon fiber is popular for reinforcements these days. I recommend recessing it a couple of millimeters beneath the gluing surface of the neck and covering it with a hardwood strip, because carbon fiber doesn't like to be sanded, filed, or planed level. The preferred glue for laying in a carbon reinforcement is epoxy. I've only used carbon fiber for reinforcement once, and it worked very well.

In the old days, hardwood reinforcements were fairly common. Many have held up very well. The million dollar question on a hardwood reinforcement is finding a piece that's stiff enough to hold up for the long term. Martin's T-bar worked well also, but I wonder if a mandolin neck might be too small for a T-bar to be practical.

I've seen quite a few warped necks on Martin guitars with the later hollow square bar, but I suspect the use of white glue was more at fault than the bar. In the old days, I might have considered a solid square steel bar for a mandolin neck reinforcement, but carbon fiber is much lighter.

I am a proponent of hot hide glue for neck to fingerboard joints. It's one of the joints that you really don't want to creep under any circumstances.
If you're not comfortable with using hot hide glue, my next choice is Titebond Original.

It's the same old song over and over again. I use these glues for most wood to wood joints in fretted instrument repair because they have proven themselves very well over many years.

As a repairman, I don't like white glues. If a joint has to be redone later, it's really hard to get rid of the old white glue to ensure the new joint will hold. And I have seen too much creeping on too many joints on too many Martin guitars assembled with white glue.

Glue in itself does not make wood stronger. But the technique of lamination can stiffen a neck, depending on the woods used, the orientation of the grain, and the type of glue. For lamination to be most effective over a long term, the cured glue should have very low elasticity. A fingerboard to neck joint is a type of lamination.

There is a banjo maker who insists on using epoxy for fingerboards. He is of the opinion that any water based glue encourages warping or cupping of the wood. He also believes that it would be easy to break an epoxy joint with heat should an instrument need repair. I heartily disagree, and if one of his instruments comes to my shop, I will ask the owner to instead send it back to the maker for the repair.

Thanks RCC56, very good breakdown of the subject. Appreciated!

[amowry]

There are many guitar builders who use epoxy for fretboards. I prefer HHG myself, but it's not unusual to use epoxy. It does have the advantage that there's no backbowing at all during glue-up because there's no moisture introduction.

[rcc56]

And repairmen will curse the epoxy users and their progeny for seven generations if they have to open and clean the joint for any reason.

Where are all the back-bowed instruments? The only time I see back-bow is on instruments that have been subjected to a gorilla with a truss rod wrench; or perhaps once or twice on instruments built out of green or unsuitably sawn wood.

I'll suggest that any builder experiencing problems with back-bowing should take a long, hard look at their tooling, clamping methods, and wood selection before blaming the problem on time-proven glues.

[Richard500]

I was trying to provoke my relative, who is a high-end Steinway rebuilder and adjuster, when he first showed me what a piano action consisted of: myriad little pieces of wood, glued up, felt parts, no moisture barriers, etc. To any engineer, dinky beyond salvation. The pianos he works on need professional tuning for each concert, and they have all the stability you’d expect from the best of 18th century design. So why not some plastic? Some epoxy? Some titanium? Synthetic felt? A few bearings where it counts?
Of course, that’s his livelihood, and hide-glue-bound tradition I was poking, but he did explain what happened to the plastic low-end piano actions of the ‘50s - disintegration! And how the concert pianists depend, for their jobs, on nothing at all being different.
So here’s to that seventh-generation downstream luthier, cursing the ancients who had civilization and chemistry, and screwed up all those mandolins.

[rcc56]

I'm always in favor of advancing the craft. But before I abandon time-tested techniques and materials and replace them with experimental ones, I want the reasoning behind the techniques to be sound, be willing to deal with the consequences if the experiment fails, and remember that the next guy who has to repair the instrument might be me.

You have to find a balance, and consider each job individually. Hide glue isn't always the most practical stuff to use, but it works. Aliphatic resins such as Titebond Original work also, and are more practical, but are more prone to creep and in many cases more difficult to disassemble. Sometimes, one is the better choice, sometimes, the other.

Epoxies work also, but are messy, difficult to disassemble, difficult to remove, and create a problem if they get on finished surfaces. I have only found it necessary to use epoxies a handful of times over many years of working on instruments. It is probably the best glue for installing carbon or metal neck reinforcements.

Something I am experimenting with: Lokweld melamine glue for binding repair on existing instruments. It's formulated for bonding non-porous surfaces to wood and is non-invasive to finishes. It's bonding strength is less than I would consider to be ideal, but I am willing to take that risk for binding repair. If I get a failure, the work can be re-done with one of the "traditional" glues that are all, unfortunately, invasive to finishes.

It's unproven. Try it at your own risk. I'm willing to take the gamble, since I'm tired of cleaning up the finish damage that often results from plastic cements or super glues.

Keep your tools sharp, your joints clean, and your mind clear.