Neck Problem

Construction and repair of Classical Guitar and related instruments
powermrk
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Neck Problem

Post by powermrk » Fri May 17, 2019 1:17 pm

If a guitar's neck isn't straight (bent forward), I would like to know usually how to fix it?
After fixing, does it affect the tonal quality?
Thanks in advance!

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RJVB
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Re: Neck Problem

Post by RJVB » Fri May 17, 2019 2:36 pm

AFAIK little bit of bending is normal and called relief; it ensures you can stop the string at say the 12th fret and not have it touch the lower frets. In an acoustic guitar the neck contains a truss rod that can be used to correct the straightness (up to a certain degree). They're unusual in classical guitars so I'll let more experience members answer the other questions.
Gretsch G9240 "Alligator" wood-body resonator converted to non-metal strings (China, 2018?)
Bolink baroque violin (Hilversum, 1982)
Formerly: Brian Cohen baroque violin (London, 1985), Nadegini modern violin (Paris, 1924)

Marcus Dominelli
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Re: Neck Problem

Post by Marcus Dominelli » Fri May 17, 2019 2:44 pm

You probably know that a certain amount of forward bend (aka 'neck relief) is expected, but if it's excessive, the first thing a repairer might do is heat up the neck, and clamp the neck flat, while still hot, and let it cool while clamped. If the glue used is water based, like titebond, this technique can be successful. It will not work with a fingerboard that was glued on with epoxy or cyanoacrylate glue.

This technique is only going to work if the bowing problem was caused by "joint creep" or failure of the glue line between the fingerboard and neck wood. If the neck is just not stiff enough, due to either poor quality woods, or not enough wood, then you can expect that this "fix" would not work. If this is the case, then the fingerboard would need removal, and a truss rod or graphite rods of some kind would need to be inserted in the neck.

Usually a repairman would try the cheaper option first.

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RJVB
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Re: Neck Problem

Post by RJVB » Fri May 17, 2019 6:34 pm

Is there a rule of thumb ("recipe") for checking neck relief on a classical guitar or a nylon-stringed one in general? My luthier showed me one but I forgot the details and since he usually works on steel-stringed guitars it might not be the optimal for nylon strings.
Gretsch G9240 "Alligator" wood-body resonator converted to non-metal strings (China, 2018?)
Bolink baroque violin (Hilversum, 1982)
Formerly: Brian Cohen baroque violin (London, 1985), Nadegini modern violin (Paris, 1924)

OldPotter
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Re: Neck Problem

Post by OldPotter » Fri May 17, 2019 8:50 pm

Is there a rule of thumb ("recipe") for checking neck relief on a classical guitar
Just google "neck relief on a classical guitar" and you will see several threads on the delcamp forum. I'm not sure there is a straightforward answer.
"When I was younger, I could remember almost everything, whether it happened or not." Mark Twain

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RJVB
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Re: Neck Problem

Post by RJVB » Fri May 17, 2019 8:57 pm

Thanks.

So it's not something like "do this, and string and fret should kiss but not french kiss"? :) (free after a friend, about disc brakes)
Gretsch G9240 "Alligator" wood-body resonator converted to non-metal strings (China, 2018?)
Bolink baroque violin (Hilversum, 1982)
Formerly: Brian Cohen baroque violin (London, 1985), Nadegini modern violin (Paris, 1924)

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Ken Whisler
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Re: Neck Problem

Post by Ken Whisler » Fri May 17, 2019 11:35 pm

RJVB wrote:
Fri May 17, 2019 6:34 pm
Is there a rule of thumb ("recipe") for checking neck relief on a classical guitar or a nylon-stringed one in general? My luthier showed me one but I forgot the details and since he usually works on steel-stringed guitars it might not be the optimal for nylon strings.
Put a capo on the 1st fret, fret the 6th string at the 12th fret and using a finger on your free hand, -lightly- tap the 6th string @the 7th fret area. You should feel a -tiny- bit of space before the string hits the fret. If you feel a little more give, eyeball it sideways into good light. A decent amount of relief should be very minimal but present. If the gap is more than about the thickness of a business card, you have got a forward bow.

Edit to add: nylon strings need more room to vibrate than their steel string counterparts, but that is addressed with action. That is why classicals usually have higher action than steel strings.
Ken Whisler, guitarist and luthier

powermrk
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Re: Neck Problem

Post by powermrk » Sat May 18, 2019 4:11 am

Marcus Dominelli wrote:
Fri May 17, 2019 2:44 pm
You probably know that a certain amount of forward bend (aka 'neck relief) is expected, but if it's excessive, the first thing a repairer might do is heat up the neck, and clamp the neck flat, while still hot, and let it cool while clamped. If the glue used is water based, like titebond, this technique can be successful. It will not work with a fingerboard that was glued on with epoxy or cyanoacrylate glue.

This technique is only going to work if the bowing problem was caused by "joint creep" or failure of the glue line between the fingerboard and neck wood. If the neck is just not stiff enough, due to either poor quality woods, or not enough wood, then you can expect that this "fix" would not work. If this is the case, then the fingerboard would need removal, and a truss rod or graphite rods of some kind would need to be inserted in the neck.

Usually a repairman would try the cheaper option first.
My classical guitar is very old made in 60's. The neck problem probably was caused by improper use/storage I guess. I haven't seen my guitar yet but according to a luthier's report that the neck apparently needs to be fixed because of the forward bent.

I will find a local repairman to fix the problem. But before that, I would like to know more about the fixing methods and options in order to know what is the best way to repair it while dealing with a repairman.

Another thing I would concern is would this kind of neck problem contribute any degree of negative effect on tone after repair?

Marcus Dominelli
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Re: Neck Problem

Post by Marcus Dominelli » Sat May 18, 2019 4:31 am

powermrk wrote:
Sat May 18, 2019 4:11 am
My classical guitar is very old made in 60's. The neck problem probably was caused by improper use/storage I guess. I haven't seen my guitar yet but according to a luthier's report that the neck apparently needs to be fixed because of the forward bent.

I will find a local repairman to fix the problem. But before that, I would like to know more about the fixing methods and options in order to know what is the best way to repair it while dealing with a repairman.

Another thing I would concern is would this kind of neck problem contribute any degree of negative effect on tone after repair?
It's not possible to know exactly which approach to take with your guitar. It could have a neck angle problem and/ or a neck relief problem. So you can check the relief in the fingerboard using the method that Ken just described.
Neck angle is not as easy to determine, but if the action is playable (let's say 3.5 to 4mm high off the 12 fret for the low E string, and 2.75 to 3mm high off the 12th fret for the high E string) and there is still a little room to drop the saddle, if needed, then your neck projection is OK.
So these things need to be accurately determined before any approach toward a repair can be determined. Different repairers will take different approaches depending on many factors.

If you can get a hold of the guitar, do these tests (for relief and neck angle) then the luthiers here will be able to give you a much better diagnoses.

As for negative effect on tone, I would doubt that any good repair job which optimizes neck relief or neck angle would negatively affect the tone.
cheers

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RJVB
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Re: Neck Problem

Post by RJVB » Sat May 18, 2019 8:17 am

Ken Whisler wrote:
Fri May 17, 2019 11:35 pm
Put a capo on the 1st fret, fret the 6th string at the 12th fret and using a finger on your free hand, -lightly- tap the 6th string @the 7th fret area.
Thanks, that corresponds to what my luthier showed me (or what I remember of it), except I'm certain he didn't use a capo.
Gretsch G9240 "Alligator" wood-body resonator converted to non-metal strings (China, 2018?)
Bolink baroque violin (Hilversum, 1982)
Formerly: Brian Cohen baroque violin (London, 1985), Nadegini modern violin (Paris, 1924)

powermrk
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Re: Neck Problem

Post by powermrk » Sat May 18, 2019 9:23 am

Marcus Dominelli wrote:
Sat May 18, 2019 4:31 am
powermrk wrote:
Sat May 18, 2019 4:11 am
My classical guitar is very old made in 60's. The neck problem probably was caused by improper use/storage I guess. I haven't seen my guitar yet but according to a luthier's report that the neck apparently needs to be fixed because of the forward bent.

I will find a local repairman to fix the problem. But before that, I would like to know more about the fixing methods and options in order to know what is the best way to repair it while dealing with a repairman.

Another thing I would concern is would this kind of neck problem contribute any degree of negative effect on tone after repair?
It's not possible to know exactly which approach to take with your guitar. It could have a neck angle problem and/ or a neck relief problem. So you can check the relief in the fingerboard using the method that Ken just described.
Neck angle is not as easy to determine, but if the action is playable (let's say 3.5 to 4mm high off the 12 fret for the low E string, and 2.75 to 3mm high off the 12th fret for the high E string) and there is still a little room to drop the saddle, if needed, then your neck projection is OK.
So these things need to be accurately determined before any approach toward a repair can be determined. Different repairers will take different approaches depending on many factors.

If you can get a hold of the guitar, do these tests (for relief and neck angle) then the luthiers here will be able to give you a much better diagnoses.

As for negative effect on tone, I would doubt that any good repair job which optimizes neck relief or neck angle would negatively affect the tone.
cheers
Thank you Marcus

Stephen Faulk
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Re: Neck Problem

Post by Stephen Faulk » Sat May 18, 2019 2:39 pm

I’ve seen this particular guitar, I forwarded it from Japan.

The neck angle is fine, the problem is the neck is bowed forward from about the 7th fret to the nut, with the most of the bow kicking in between the 5th and 3rd fret.

Bottom line, it needs a carbon fiber spar glued into a routed channel under the board and ideally a new board and frets, but you could get by with the old board and new frets.

Otherwise it’s a 55 year old Kono model #5 in good condition with no other problems but some tape residue left on the tail join where someone presumably taped a mic cord.

The guitar was shipped with the strings nearly at full tension. I let them slack when I repacked it for international shipping.

It’s worth putting whatever a repair person estimates, it’s a potential to be a satisfying playing guitar is pretty good.
Patience at the bending iron pays in rounded dividends!

Stephen Faulk
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Re: Neck Problem

Post by Stephen Faulk » Sat May 18, 2019 2:44 pm

As far as tone after a carbon fiber spar, it’s very likely it will not change the sound perceptibly at all. But one thing about neck stiffening repairs, in observation and experience from doing them, they usually help the sound and feel of the guitar, not hinder it.

This particular guitar isn’t going to play very well until the bow problem is fixed. I didn’t bother measuring the the amount of outness, but by eye I could tell. I also held the neck in my hands and flexed it back straight. The strings lowered back down to a good height.

Which tells me a neck stiffening procedure is needed. The saddle mound is high on this bridge design, I wouldn’t cut it down or modify it to get an action, I would stiffen and flatten the neck, then plane a new fingerboard to work with the bridge as is. A lot of people are tempted to cut down high saddle mounds, but it’s not a good idea.

The strings as a mentioned were almost full tension and the d string had snapped at some point, but I plucked on it and tried the five strings. It’s a very nice sounding instrument even with worn out strings. This guitar deserves a full work up to original stats.
Patience at the bending iron pays in rounded dividends!

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RJVB
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Re: Neck Problem

Post by RJVB » Sat May 18, 2019 4:36 pm

Stephen Faulk wrote:
Sat May 18, 2019 2:44 pm
I also held the neck in my hands and flexed it back straight. The strings lowered back down to a good height.

Which tells me a neck stiffening procedure is needed.
Should it even be possible to do that if you're not big and green or put your knee into it as well?
Gretsch G9240 "Alligator" wood-body resonator converted to non-metal strings (China, 2018?)
Bolink baroque violin (Hilversum, 1982)
Formerly: Brian Cohen baroque violin (London, 1985), Nadegini modern violin (Paris, 1924)

powermrk
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Re: Neck Problem

Post by powermrk » Sun May 19, 2019 5:29 am

Stephen Faulk wrote:
Sat May 18, 2019 2:44 pm
As far as tone after a carbon fiber spar, it’s very likely it will not change the sound perceptibly at all. But one thing about neck stiffening repairs, in observation and experience from doing them, they usually help the sound and feel of the guitar, not hinder it.

This particular guitar isn’t going to play very well until the bow problem is fixed. I didn’t bother measuring the the amount of outness, but by eye I could tell. I also held the neck in my hands and flexed it back straight. The strings lowered back down to a good height.

Which tells me a neck stiffening procedure is needed. The saddle mound is high on this bridge design, I wouldn’t cut it down or modify it to get an action, I would stiffen and flatten the neck, then plane a new fingerboard to work with the bridge as is. A lot of people are tempted to cut down high saddle mounds, but it’s not a good idea.

The strings as a mentioned were almost full tension and the d string had snapped at some point, but I plucked on it and tried the five strings. It’s a very nice sounding instrument even with worn out strings. This guitar deserves a full work up to original stats.
Thanks Stephen, I know much better my guitar's condition, you always help :D

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