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.. and so the braces comes off and it's being redone. Any suggestion on avoiding this in the future? I kept the top/brace in the dry room for days before I even braced it, but I used water to clean up the excess glue after putting a brace on - Do you think that may have wicked excess moisture into the top causing the potato chip? I'm doing a flat top because I'm sick of having weird neck angle on the finished guitar. Even 25' is a huge angle, requiring an excess of 5 degree of neck angle (I kid you not!). I do not have any other radius but this time I am thinking to brace the top in a 25' dish, and then glue it to a flat rim.

The UTB is also too small, I am making it much larger next time.

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Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

What was the RH when you braced it versus when it potato chipped? It could be that you just hit an unusually dry day, and could have waited it out. I brace at 30-35%, but my room humidity gets down to 20% with heating in the winter, so my plates could potato chip too. If I braced them at 20%, they might poof up too much in the summer when it gets up to 70-80%.

Flat tops will definitely go concave more quickly than dome tops. There is no "perfect" solution to humidity, especially for all different climates. Yours is probably the most challenging, if you want your guitars to be able to survive anywhere else. Learn the variables, and pick your poison.

I have a humidity controlled room that is maintained at 50%, otherwise the humidity is never less than 80% outside of that room. I envy low RH environment sometimes because humidifying is a lot easier than dehumidifying.

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Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

Man, something's really strange there.
All my builds have used a 25' radius top, FB about 6mm final thickness, and have never been more than 2 degrees off the right angle where the neck meets the body on a fully radiused rims.
I've never heard of anyone else much different to that angle before.
Have you actually checked the radius of the dish? (5 degrees would be more like a 15' radius)
http://liutaiomottola.com/formulae/sag.htm for measurements.
Trevor Gore's book talks about a 30' radius top being "flat" for the neck alignment for a 14mm string height at the saddle.

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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.

I checked it, it checks out at 25' radius. Perhaps something else was up, like maybe the neck block wasn't perfectly right angle to the radius dish so it created a higher angle than normal, I don't know. I think however I'll radius all the braces except for the UTB and then glue it to a flat rim. The hope is that the top/side angle should be perfectly square...

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

Could be the humidity. Brace in 50% and take it up to 80%, it will poof up a lot and have more angle in the fingerboard extension area.


So you braced in 50%, and it potato chipped as soon as it was dry? Or sometime later, but still no big humidity drop?

I suppose it's possible the water from glue cleanup would swell it before the glue had time to lock the fibers in place, but I'm not sure how likely that is to happen.... hopefully someone else with personal experience will come by. I've always avoided water on brace glue cleanup out of fear of that happening, but it does result in a bit of residue being left over. If it's hide glue, it can be cleaned with water after the glue under the brace is good and dry, but it would be quicker to do while it's still wet in the first place. I usually just leave the residue, but a lot of builders (and buyers) are obsessive about flawless box insides, so I'd assume they're using water, and hopefully can provide info.

Yeah the radius issue seems weird. Typically the UTB only gets very little radius, almost flat, or 60'-ish radius, and the sides are sanded just slightly to achieve the correct neck angle. I dont know the method you are using, but a 5 degree neck angle seems waaaayayyy too much. I dont use a dish for top braces, but shave off 1/16" at the ends of the UTB, along with a very slight bit of sanding of the rims above the soundhole, on a sanding board with a thin shim under the tail block (search the Hesh method). This gets me about .080-.090" of space at the saddle with a straigt edge placed above the soundhole. If it's not in that range, keep sanding the rims until it's correct. This of course has to be done before gluing up the top. Thats how I do it. Very important to get the neck angle correct.

About the braces...were the braces and top in the climate control room for a good while before you started milling and building? Just thinking , if you brought the braces in like the day or day before you cut them up, they could cause a potato chip top as they dry out while attached to the top. I like to get all my materials in the climate controlled area at least a month (more is better) before starting to work the wood. Even longer with neck blanks. Just to be safe.

How fast does guitar wood lose moisture vs. gaining them when it comes to changes to RH? I take them out of the room to work on them (the climate control room is very small and hot, controlling the main shop will cost an unreasonable amount of money but when the AC is turned on the humidity drops to less than 45%). I'm just thinking I should not have used water for clean up... I had to use quite a bit of water and I fear the wood probably absorbed quite a bit. I left the loose parts inside the dry room for days before I glue it up.

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

On my first few builds I used water to clean up and didn't have any issues. I don't think it's enough water to make a difference if just using a small damp rag, with the water local to the glue area. If one was using a large soaking wet rag and getting most of the top soaking wet I bet it could make a difference.

It's good practice to leave a braced top (and back) in the climate controlled room at all times. Not a good idea going from 50 to 80% RH with a loose top (or back). you're just asking for Pringles.

That might have been the problem, I used a soaking wet rag because I wanted to get it CLEAN... probably not such a good idea. But the top didn't potato chip until I left it alone, unsupported in the climate control room, so I don't know what happened. It also only happened when I scalloped the braces.

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Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

I cant specifically answer your question. Too many variables...wood thickness, species, moisture content, etc. I have had 1/2" thick bracewood go banana on me after several weeks doing just fine in my climate controlled room.

It's not a good idea to have your build in a highly fluctuating RH environment, especially when the plates are loose.

I find that water from cleaning up hide glue can temporarily swell and distort soundboards, etc, but they return back to normal pretty quickly. Moisture introduced from cleanup, bending, steaming dents, etc, is very different from the moisture in green wood. Still, it's a good idea to minimize it. I scrape up 95% of hide glue squeeze out when it's in its snot phase, maybe 30 min after glue up. Then use a merely damp rag after the clamps come off and glue is completely dry.

The ambient humidity is really what the issue is. Also, 'baking' helps to stabilize tops. I'm sure there is plenty in the archives. I always have to struggle with tops moving too. There's pretty rapid humidity swings where I live. Best to get them on the boxes quickly.

So you're saying it's better to maintain a 80% RH then? Humidity doesn't fluctuate much at all in Taiwan in the absence of climate control but it's consistently very high.

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

The water could have been the issue. Try using less glue, and make a glue clean up stick out of a thin piece of spruce, or get the LMI glue cleaning chisel. My thoughts are the real issue is that your brace wood had not yet acclimated to the climate room before you started cutting it, and/or moving from different RH.

80% seems high, but the conventional wisdom is to build in the same RH as where the guitar will live after it's built. Usually people in the climate I live in build around 40-50% RH.

So if a musician travels between varying RH area (like a gig in a tropical rainforest, followed by a gig in say Dubai a week later) would have a hard time with his guitars?

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

Yes. This musician would definitely want to have some case climate control. An all carbon fiber guitar would be even better!

Is your glue up done in the humidity controlled room? If not, it should be. I have a small room in the shop which is temp & humidity controlled. I do much of my work in the uncontrolled space, but the go-bar deck is in the smaller room. All of the sensitive gluing operations are done there, under controlled conditions.
I thin my plates down to about .030" more than the finished dimension & then leave them in the controlled space for a week or two (more, if I haven't had the wood stored for more than 6 months) before jointing & gluing the plates. Then I let them dry a few days before bracing.
Our humidity varies widely & is often in the mid 80% range... Sometimes, much higher. With heat & dehum, it's no problem maintaining the humidity (I keep mine at around 42%), without making the room too hot to work in. During the warmer months, I use a small air conditioner to help control the conditions & keep the room a comfortable temperature.
I built the controlled room years ago, after having a disaster similar to the one in your pictures.

I did the glue up in the controlled room. Not sure what happened, either the top shrank in the wrong direction or the brace grew in length. When I finally planed all the braces off I discovered the top was actually curled inward.

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

- how old is your top wood.
- storing it a few days in your dry room is way too short, a few month is at least necessary.
- when it is very hot th RH is not low!!!!! you need about 38-45 % by about 20 degrees. It is called realtv humihidty and not absolut humihidty!!!!
- shrinkage rate : google this, in lenght wood is more or less not shrinking, well at least nothing compared to shrinkage in width and highth.
- cleaning up with a bit of water is totally ok, but not too much. Important: Use old wood, store it dry room for a few month, join it, brace it, assamble the box, all in the same dry room. Do not take it out for too long.

Everything else will end up in a random guess work about neck angle, playability and of course the sound.

cheers, alex

William Cumpiano gives some advice about this same thing in News Letter 22.


Sent from my iPhone using Tapatalk 2

Months? If the wood is green, then yes... but dry wood thinned to 3mm or so should acclimate within hours.

So, I guess the verdict is water from glue cleanup, because there doesn't seem to be any other explanation. Whaddya know, my paranoia was well founded after all

And 45-50% sounds like good bracing RH for your region. It should be fine in 80%+ outdoor air, and shouldn't be too difficult to keep humidified enough not to crack in other parts of the world. I build dry because I can't humidify my whole room (too many windows) and I hate filling tons of case humidifiers all winter. Bracing in 30-35% seems to tolerate 20% to 70% no problem, and probably 80%+ but I haven't had the opportunity to test it for more than a couple hours.

The top isn't the issue, it's the braces that will cause potato chip. Braces being much thicker than tops will take longer to acclimate.

Just to be clear...the top was sunken on the outside? If so, that means that the top lost moisture after it was braced. It is the shrinkage/swelling of the top itself that is the issue, since movement of the braces lengthwise is much less.

Adding water to the top should have swelled it, making it convex on the outside.
The MC of the bracing is not the issue, because wood moves very little in the grain direction.
If you are in a hurry to acclimate the wood, sticker it and put a fan on it.
There is a simple test for determining if the wood is acclimated. Place it on a flat surface, exposing the top side only. If the wood curls up (concave on top), then it is losing moisture to the air. If it bows in the middle (convex on top), it is gaining moisture from the air.

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John

Why would the braces matter? Wood changes very little in the longitudinal direction, and they're so narrow, any width change would be very small. Maybe a 1/2" wide upper transverse brace's width shrinkage could affect the upper bout angle a tiny bit, but the others, being usually 5/16" at most, should be unnoticeable... and if they're wet and drying out, it would be in the convex direction anyway.