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 Post subject: Neck Bow
PostPosted: Fri May 07, 2021 10:19 am 
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Walnut
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I posted this in the electric forum but, this kind of seems like a universal problem and figured Id get a little more traffic here to help me out.

I'm working on a Tele Build for my daughter. I did a two piece neck and head stock with a scarfed joint as suggested here. (Mahogany & Ash) After routing and getting it sanded I noticed the neck has a bow to it. If it was complete with the truss rod and fretboard it wouldnt be a big deal as I could simply adjust it. Any ideas to get this straight before I continue installing the truss rod and fretboard? Pics file size are too big on my phone to attach, but from end to end there's probably a good 1 to 2mm bow.

Also, I should mention the truss rod slot has already been cut and fitted, along with the routing of profile of the neck is complete. Otherwise I could have maybe got away with running it through a jointer a few passes but its already at its thickness of 3/4".


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 Post subject: Re: Neck Bow
PostPosted: Fri May 07, 2021 6:57 pm 
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Koa
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I am not an expert in this at all--zero experience with this problem. However, it seems to me that if you think it would be OK if the truss rod were in and the fingerboard on, then why can't you just install the rod and glue on the fingerboard. If you support the assemble with rigid, straight boards while you glue and clamp it, if should somewhat conform to the flat surfaces.

I am reminded of a recent ruin that I did. I built a uke and had the neck so well aligned with the body that I decided to fret the fingerboard before installing it. For a caul on the fingerboard, I used a rigid thick board and wrapped a little tape on one end to be sure to distribute clamp pressure along the entire fingerboard. Well I clamped that down tight and the fingerboard and neck bent back and dried with a reverse bow. So, your assembly will take on whatever curve you force on it before the glue dries--I think.


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 Post subject: Re: Neck Bow
PostPosted: Fri May 07, 2021 9:03 pm 
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Walnut
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wbergman wrote:
I am not an expert in this at all--zero experience with this problem. However, it seems to me that if you think it would be OK if the truss rod were in and the fingerboard on, then why can't you just install the rod and glue on the fingerboard. If you support the assemble with rigid, straight boards while you glue and clamp it, if should somewhat conform to the flat surfaces.

I am reminded of a recent ruin that I did. I built a uke and had the neck so well aligned with the body that I decided to fret the fingerboard before installing it. For a caul on the fingerboard, I used a rigid thick board and wrapped a little tape on one end to be sure to distribute clamp pressure along the entire fingerboard. Well I clamped that down tight and the fingerboard and neck bent back and dried with a reverse bow. So, your assembly will take on whatever curve you force on it before the glue dries--I think.


Essentially I think that could work. I wish I could post pics on how bad the bow is. Its not that bad but, I'm just afraid of getting all that glued up and it being no good.


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 Post subject: Re: Neck Bow
PostPosted: Sat May 08, 2021 4:12 am 
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First name: colin
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Do you need 3/4" in the middle of the neck, remembering it will be tapered?
Using epoxy will resolve any potential warping/bending issues with gluing FB.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.


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 Post subject: Re: Neck Bow
PostPosted: Sat May 08, 2021 7:56 am 
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Walnut
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Colin North wrote:
Do you need 3/4" in the middle of the neck, remembering it will be tapered?
Using epoxy will resolve any potential warping/bending issues with gluing FB.


I will be taking that 3/4" down a little on the back of the neck but not too much.

And epoxy. Do you mean putting the FB on with epoxy?


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 Post subject: Re: Neck Bow
PostPosted: Sat May 08, 2021 2:34 pm 
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Colu41 wrote:
Colin North wrote:
Do you need 3/4" in the middle of the neck, remembering it will be tapered?
Using epoxy will resolve any potential warping/bending issues with gluing FB.


I will be taking that 3/4" down a little on the back of the neck but not too much.

And epoxy. Do you mean putting the FB on with epoxy?

If you take 1/8" of the neck at the nut end, and nothing at he other end (i.e. keep it at 3/4") you will reduce the middle by 1/16"
This could be used to remove a back bow of ~1.5mm if planing the top surface of the neck.
Yes, gluing the FB on with epoxy. I, and several others here use epoxy to prevent water base glue warping/ bowing the neck.
TR slot can be deepened with a a router plane, or chisel if you prefer.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.


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 Post subject: Re: Neck Bow
PostPosted: Sat May 08, 2021 3:34 pm 
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Walnut
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First name: Corey
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Colin North wrote:
Colu41 wrote:
Colin North wrote:
Do you need 3/4" in the middle of the neck, remembering it will be tapered?
Using epoxy will resolve any potential warping/bending issues with gluing FB.


I will be taking that 3/4" down a little on the back of the neck but not too much.
And epoxy. Do you mean putting the FB on with epoxy?

If you take 1/8" of the neck at the nut end, and nothing at he other end (i.e. keep it at 3/4") you will reduce the middle by 1/16"
This could be used to remove a back bow of ~1.5mm if planing the top surface of the neck.
Yes, gluing the FB on with epoxy. I, and several others here use epoxy to prevent water base glue warping/ bowing the neck.
TR slot can be deepened with a a router plane, or chisel if you prefer.


Won't epoxy crack with any possible warping in the future?


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 Post subject: Re: Neck Bow
PostPosted: Sun May 09, 2021 1:21 am 
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First name: colin
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Not really, never heard of any failure if epoxy is properly mixed and surfaces roughened as per instructions.
Try thinking epoxy/fiberglass boat (which has wooden internals epoxied in) flexing in heavy seas.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.


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 Post subject: Re: Neck Bow
PostPosted: Sun May 09, 2021 9:04 am 
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Walnut
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Joined: Sat Feb 27, 2021 5:05 pm
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First name: Corey
State: MI
Country: United States
Focus: Build
Status: Amateur
Colin North wrote:
Not really, never heard of any failure if epoxy is properly mixed and surfaces roughened as per instructions.
Try thinking epoxy/fiberglass boat (which has wooden internals epoxied in) flexing in heavy seas.


Ok. So you obviously cant just use a simple two part epoxy have to go find something with a long cure time thats pretty flexible.


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 Post subject: Re: Neck Bow
PostPosted: Sun May 09, 2021 9:12 am 
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Koa
Koa

Joined: Mon Dec 18, 2006 9:42 am
Posts: 1443
Location: United States
I tried to repair a spindle back chair with epoxy, per instructions from professional woodworker. It failed rather quickly.


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 Post subject: Re: Neck Bow
PostPosted: Sun May 09, 2021 10:07 am 
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Brazilian Rosewood
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Joined: Sun Mar 30, 2008 8:20 am
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Colu41 wrote:
Colin North wrote:
Not really, never heard of any failure if epoxy is properly mixed and surfaces roughened as per instructions.
Try thinking epoxy/fiberglass boat (which has wooden internals epoxied in) flexing in heavy seas.


Ok. So you obviously cant just use a simple two part epoxy have to go find something with a long cure time thats pretty flexible.


The fretboard adds a lot of stiffness to the neck, so you don't really want to have a "flexible" glue joint. I use West system, but there are several other good choices.
Epoxy is used to glue things to (wood, metal etc.) and repair polyester boat hulls because it adheres to polyester better than polyester adheres to polyester.


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 Post subject: Re: Neck Bow
PostPosted: Sun May 09, 2021 10:30 am 
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Walnut
Walnut

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Clay S. wrote:
Colu41 wrote:
Colin North wrote:
Not really, never heard of any failure if epoxy is properly mixed and surfaces roughened as per instructions.
Try thinking epoxy/fiberglass boat (which has wooden internals epoxied in) flexing in heavy seas.


Ok. So you obviously cant just use a simple two part epoxy have to go find something with a long cure time thats pretty flexible.


The fretboard adds a lot of stiffness to the neck, so you don't really want to have a "flexible" glue joint. I use West system, but there are several other good choices.
Epoxy is used to glue things to (wood, metal etc.) and repair polyester boat hulls because it adheres to polyester better than polyester adheres to polyester.


I guess flexible is the wrong word really but, I guess MORE flexible than a short cure epoxy that easily cracks. I guess I'd rather have a fingerboard/neck flex a little bit than have the epoxy crack and have the board eventually peel off. Just from my experience in knifemaking the type of epoxy and what your using it on is very important.


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 Post subject: Re: Neck Bow
PostPosted: Wed May 12, 2021 5:56 pm 
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Cocobolo
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Joined: Fri Nov 02, 2007 2:53 pm
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Location: Canada
I believe the term 'structural epoxy' is what is used. There's a few on the market. IIRC, Mario fretted the fingerboard. put a half inch block under each end and clamped the center down to the workbench. This gave a flat fingerboard with the frets in and then used epoxy to glue it on the neck. No bowing. Michael Greenfield uses structural epoxy as well.


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 Post subject: Re: Neck Bow
PostPosted: Wed May 12, 2021 7:10 pm 
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Koa
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I think I see some amount of overthinking and problem avoidance. I don't try to compensate for a problem during a build. I do try to fix a problem before proceeding. OP seems to have a neck that's not flat. I would be very uncomfortable about continuing work on that neck and trying to compensate for the deformation. OP didn't mention whether that neck was quartersawn or flatsawn. Might be the source of the problem if the neck was flatsawn, And the neck wood might just have come by its deformity during fabrication. I'd stop and if I had to, make another neck that's flat before attempting to install a fingerboard. Life's tough enough already.

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 Post subject: Re: Neck Bow
PostPosted: Thu May 13, 2021 1:03 pm 
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Cocobolo
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wbergman wrote:
I tried to repair a spindle back chair with epoxy, per instructions from professional woodworker. It failed rather quickly.


chair joints are the hardest joints to make well, and keep tight over the years. Typically, once they loosen, you need to re-make the spindle and re-cut the mortise if you really want it to last more than a few months. Chair joints also endure the most stress of any joint in woodworking that I know of... (never made a laminated cross-bow though:-). If done correctly, the glue isn't really doing much... if any thing. But, this isn't a furniture making thread!

For guitars, we use "Bob Smith 206 Slow Cure Epoxy" but I've also used small bottles of high-strength 30-min that you can get from ACE or similar. We only put epoxy under fret boards and for shell inlay... specifically for the reason mentioned above, avoiding moisture in the neck.

All that said, my vote would be the suggestion to use the jointer in increasing partial passes to reduce the thickness at the nut until you are flat... assuming you can afford to lose enough wood for that to work.


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