Question for Luthiers: thinning top on a finished guitar

Construction and repair of Classical Guitar and related instruments
SteveL123
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Re: Question for Luthiers: thinning top on a finished guitar

Post by SteveL123 » Tue May 08, 2018 12:02 am

MessyTendon wrote:
Mon May 07, 2018 4:45 pm
(...............)
The thing to do is get in there and check out the braces. If they are the factory braces which are more or less rectangular...give them some contour on the sides.

(..............)
They are all rectangular. I will trim them. Thanks!

MessyTendon
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Re: Question for Luthiers: thinning top on a finished guitar

Post by MessyTendon » Tue May 08, 2018 3:21 pm

Be carefully with those braces...it's a PIA the shave braces with a fully sealed guitar.

But if you have some usb device with a cam to look in it should be easier. Scallop the ends of the braces and thin the sides of the brace...a little bit should work.

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Les Backshall
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Re: Question for Luthiers: thinning top on a finished guitar

Post by Les Backshall » Tue May 08, 2018 5:38 pm

SteveL123 wrote:
Mon May 07, 2018 11:53 pm
Les, Do you mean the Stanley blades in the shape of a trapezoid? I'll give it a try for sure. Thanks!
Yes, they're the ones. I actually use Fat Max - rather more expensive, but hold an edge for quite a while.

Les
Lester Backshall, Guitar Maker - Aylesbury UK

madrilla
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Re: Question for Luthiers: thinning top on a finished guitar

Post by madrilla » Tue May 08, 2018 7:08 pm

I was wondering if you can use a heat gun or a hair dryer to remove the finish. I read somewhere that it can peel off easily when heated up.

MessyTendon
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Re: Question for Luthiers: thinning top on a finished guitar

Post by MessyTendon » Sat May 12, 2018 4:23 pm

Heat gun would risk screwing up the glue even if it is PVA glue...I wouldn't want that level of heat around.

madrilla
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Re: Question for Luthiers: thinning top on a finished guitar

Post by madrilla » Sun May 13, 2018 12:06 am

MessyTendon wrote:
Sat May 12, 2018 4:23 pm
Heat gun would risk screwing up the glue even if it is PVA glue...I wouldn't want that level of heat around.
Thanks. Breaking down the glue was also my concern. If there is a time limit you can apply the heat without affecting the bonds then that would give more confidence. But it is unknown territory and therefore risky as you said. It's probably better to sell the guitar and buy another one.

SteveL123
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Re: Question for Luthiers: thinning top on a finished guitar

Post by SteveL123 » Wed May 16, 2018 8:07 pm

I have not done more scraping/ removal of the finish other than the areas under the strings between bridge and sound hole. I was going to add a little glue where there is a little separation under the middle 4 strings so made this clamp following Michael.N's idea in a post of his. The gap is about 0.005" (0.127 mm) about 1/4" deep (6 mm) at its deepest.

Am I correct in thinking that there is no way to glue this kind of a gap successfully with hot hide glue or Titebond?

Right now the guitar is strung and I am playing it and plan on scraping/ playing while observing the change in tone if any.

I think the bridge has to come off eventually so that I can shape the area under the bridge so there is no gap.
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SteveL123
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Re: Question for Luthiers: thinning top on a finished guitar

Post by SteveL123 » Wed May 23, 2018 12:50 am

The scraping of the finish as in the pic with the bridge clamp did not change the tone much. Today, I scraped the treble side of the guitar (while the strings were tuned to pitch) and when I was done, I noticed quite a bit of difference. The guitar is more responsive and a bit louder! I am surprised since it's raining here today and the RH is 60%, which normally makes the guitar sound duller and lose a bit of volume.

I'll play the guitar for a week or so then scrape the bass side and hope for more better changes. Note: I taped the sound hole so the extremely fine and dusty shavings of the finish do not get inside.
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malc laney
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Re: Question for Luthiers: thinning top on a finished guitar

Post by malc laney » Wed May 23, 2018 7:36 am

Get this wrong , you land up with a hairy guitar!

Mr.Rain
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Re: Question for Luthiers: thinning top on a finished guitar

Post by Mr.Rain » Wed May 23, 2018 2:18 pm

My 2 cents I would go for a different approach, as altering the top thickness sounds super tricky to me.

Actually I did it before, I shaved the braces of a studio guitar from the soundhole (using a "finger plane", a spruce piece and sandpaper ) the original braces were very tall (5mm), shaved them down. 1st to 4mm, then 3.5mm and then to 3mm (finally rounded the bars!). The guitar was becoming louder on each "reduction", warmer and more open. At the end the result was an instrument you could play and that sounded like a guitar (not the trebly, 0 bass instrument it was when new)..

Removing the thick lacquer will improve the sound as it is a poly-coffin, making the guitar even tighter...
Watchout for RH, no finish means the changes will affect it even more (what you can perceive as a warmer tone, can be dimmed trebles in a wetter day...)

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Pat Foster
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Re: Question for Luthiers: thinning top on a finished guitar

Post by Pat Foster » Fri May 25, 2018 12:11 am

For brace shaving on a closed up guitar, I like this Zona spokeshave with its "ears" removed. I also use it during initial construction because it's so easy to use. I usually pull it rather than pushing, though it works both ways. It's easy to keep on the brace by using the index and middle fingers to pull from the back of it so that the fingers form a guide of sorts. That way, you don't need to see what you're doing (except to check your progress).It will get well down the sides of a brace, close to the top. Learned this tip in the 70s from the folks at Jon Lundberg's, known for hotrodding Martins, back when that was on OK thing.

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SteveL123
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Re: Question for Luthiers: thinning top on a finished guitar

Post by SteveL123 » Fri May 25, 2018 2:42 am

Thanks for the tip about the modified Zona Spokeshave Pat Foster! I was going to get some violin brass thumb planes from China but this looks like it will work just as well if not better. Cheaper too! Just ordered one for $7.80 with free shipping from a Walmart affiliate Blackstone Industries.

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Pat Foster
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Re: Question for Luthiers: thinning top on a finished guitar

Post by Pat Foster » Fri May 25, 2018 2:47 am

SteveL123 wrote:
Fri May 25, 2018 2:42 am
Thanks for the tip about the modified Zona Spokeshave Pat Foster! I was going to get some violin brass thumb planes from China but this looks like it will work just as well if not better. Cheaper too! Just ordered one for $7.80 with free shipping from a Walmart affiliate Blackstone Industries.
The edge of the iron will likely be poorly dressed, so you might need to spend some time on that. Set it to take thin shavings. Practice on dummy braces on scrap wood . . in the dark!

SteveL123
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Re: Question for Luthiers: thinning top on a finished guitar

Post by SteveL123 » Fri May 25, 2018 2:50 am

Mr.Rain wrote:
Wed May 23, 2018 2:18 pm
My 2 cents I would go for a different approach, as altering the top thickness sounds super tricky to me.

Actually I did it before, I shaved the braces of a studio guitar from the soundhole (using a "finger plane", a spruce piece and sandpaper ) the original braces were very tall (5mm), shaved them down. 1st to 4mm, then 3.5mm and then to 3mm (finally rounded the bars!). The guitar was becoming louder on each "reduction", warmer and more open. At the end the result was an instrument you could play and that sounded like a guitar (not the trebly, 0 bass instrument it was when new)..

Removing the thick lacquer will improve the sound as it is a poly-coffin, making the guitar even tighter...
Watchout for RH, no finish means the changes will affect it even more (what you can perceive as a warmer tone, can be dimmed trebles in a wetter day...)
Thanks for the advice Mr.Rain! I do have 2 Hacklinger gauges that I made to measure top thickness but that probably is not the tricky part.

I do keep the guitar in a case with Humidipaks when not working on it.

SteveL123
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Re: Question for Luthiers: thinning top on a finished guitar

Post by SteveL123 » Fri May 25, 2018 2:52 am

Pat Foster wrote:
Fri May 25, 2018 2:47 am
(........................)
The edge of the iron will likely be poorly dressed, so you might need to spend some time on that. Set it to take thin shavings. Practice on dummy braces on scrap wood . . in the dark!
Will do thanks! I always take a few dry runs when doing something for the first time till I feel proficient.

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