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Warped top and back!
Author
Post
enalnitram (Martin Lane)

Total Topics: 47
Total Posts: 338
My second build just suffered a major setback.

I had the rim put together. And I had the (african mahogany) top and back braced. The rim had been notched to accept the top and back. I glued the top to the rim. When I did this, it wasn't until after the top was on, that I noticed I had done a bad job of getting the rim flat enough for the top. One side of the upper bout was slightly higher than the other.

After this happened, I vowed to never use sanding sticks again and to go with radiused dishes from now on. (as well as trying to do a better job at measuring things).

So I took the top off, and started coming up with a plan to obtain or buy some dishes.

A few days after the top was removed, I noticed that the top had warped, and badly. So, I then looked at the back, and it too had warped. Even though my braces were radiused, the top was now concave! The back wasn't concave, but was mostly flat, much flatter than its original 15' radiused shape.

When I take a dampened cloth and wet the top and back, both return part way to their former shape, but not all the way.

I searched here and found a few threads where others had exactly the same problem. And I've asked around about it. The theory that sounds the most plausible to me is that the top and back hadn't sufficiently dried out before I started to build with them. What do y'all think?

While I was asking around, one friend even told me that it sounds like if I had waited a few more days, my top would've probably cracked if it had still been glued to the rim when it warped.

I'm going to take all the bracing off of my top and back using a hand plane, and when I get close to the wood, I'm going to get the remainder off using heat.

This is a heartbreaker for sure, because I had a lot of time in it, but I also feel confident that the top and back can be salvaged and that the next bracing job will be even better.

I'm going to try my hand at making my own bracing. How hard can it be? Don't laugh, but I was at Menards today and found some very clear tightly grained spruce in the building materials. they were 8 foot long 2"x2"s marked SPF. so I bought a couple of pieces, and plan on splitting it this weekend to see what happens.

As long as I'm building things, I'm now working on a drying cabinet also....

Jan 08, 10 | 10:45 am
Freeman

Total Topics: 27
Total Posts: 668
humidity humidity humidity

Ideally your wood was dried to around 40 percent RH and after you received it from the supplier you let it stabilize in your shop before you start. You should build at that RH and of course, maintain that thru the life of the guitar. Even small swings can have dramatic affects on the unbraced pieces.

If nothing else, get a good hygrometer (cigar shop or guitar store), calibrate it and put it where you can see it in your shop. Not sure about your "drying cabinet" - don't get it too dry or you'll have other problems.

Making braces isn't at all hard. Many argue that they should be split but if the wood is well quarter sawn, just band sawing them works fine. You really don't need to buy that big a piece (altho now you can build a few hundred guitars or maybe a biplane), LMI and others sells smaller pieces.

btw - here was my education in humidity

http://www.kitguitarsforum.com/forum/threads.php?id=2673_0_2_0_C

Jan 08, 10 | 2:00 pm
Ken Cierp

Total Topics: 58
Total Posts: 2262
It's hard to comment without having the components at hand -- but if the materials were purchased from a reputable suppler more than likely it was dried to lower than 6% -- again I would have to actually see the problem but chances are unless the assmbly looked like a kettle cooked potato chip I'd go ahead with the build (the assmbly is on the small side of the Expansion/Contraction cycle) --- if this were summer in Michigan I would be more concerned.

If you are going to use local spruce get aircraft grade from a hobby shop it will be dried properly --- the wood at the big box stores is dried between 13%-20% moisture content. In my opinion using that stuff is really asking for trouble.

Ken

Kenneth Michael Guitars est. 1978

Jan 08, 10 | 3:13 pm
Ken C

Total Topics: 30
Total Posts: 554
Sounds like your issue is more due to a change in humidity than an issue with your wood sources. Humidity changes can be bugger. I had my first bout with a big humidity change recently. I put the top and back on my J-185 late fall when we weren't running any a/c or heat here in Michigan. My gauge showed the humidity around 50%. I built the top with a 40' radius and the back with a 15' radius. After the top and backs were on, I threw on my radius gauges and was very pleased with my handiwork. I then set the guitar aside for about a month while I sprayed the finish on the madrose OM. When I got back to the J-185, the top had sunk in and was a bit concave. The back radius had dropped to about 40'! Temps had turned cool and we were now running the furnace consistently.

I immediately changed the evaporative panels in my furnace humidifier and purchased a separate humidifier. The humidity is now consistently back to around 40%, and the radius has mostly come back to both the top and the back.

Ken

Jan 08, 10 | 5:11 pm
Ken Hundley

Total Topics: 40
Total Posts: 2169
One of the most important things you can do when storing thin flat panels is to "sticker" them. Many times, the warping happens because one side shrinks or expands faster than the other....simply because of the difference in exposure to the environment. I have seen my tops do that, and simply propping them on an edge with equal airflow straightens them right back up. If you take a top or back off, or store it flat on a surface with no gap beneath it, it will warp every time the environment changes.

Jan 08, 10 | 7:28 pm
enalnitram (Martin Lane)

Total Topics: 47
Total Posts: 332
Thanks for the input guys. I tried to get a visual tonight but it is difficult to see in pics. Imagine a 25' radius going the wrong way across the lower bout on the top.

So please correct me if I'm wrong. But it sounds to me like what I should do, based upon what each of you is saying, is:

1. remove the bracing from the top and back.
2. wait a little while. (but how long?)
3. cut some brace wood from the lumber yard spruce, but save it for my young son to use when he is older (if I want him to suffer)
4. purchase some nice brace stock
5. install that on the acclimated top and back and then continue.

I live in Grand Rapids, Michigan. we have had a cold snap here, and lots of snow. but I have a med room size humidifier in my small work area and while rh is not great, I didn't think it was too bad either... in the 30's.

Jan 08, 10 | 8:42 pm
Ken Cierp

Total Topics: 58
Total Posts: 2262
A top or back that was dried to 6% or so will acclaimate to the room in less than 24 hours --- the temperature change in the from will affect the MC of the material. So if the room is cold in the morning and the temp increases 20 - 30 degrees or so, the humidity will drop quickly as will the MC in the wood -- this stuff is very thin so it gains and releases moisture in a hurry. Just take a hair dryer warm one surface within minutes it will cup that way flip it over let it set a while warm that surface and it will cup in the opposite direction. One surface will tend to cup more naturally and should have been used for the inside so it more readily accepted the contour. The brace wood will sometimes have a slight natural bow as well, and should be shaped and glued with this in mind.

I am not making any recommendations --- without actually having the parts in my hands it would just plane be a WAG.

Ken

Kenneth Michael Guitars est. 1978

Jan 09, 10 | 7:51 am
Freeman

Total Topics: 27
Total Posts: 668
It happened to me on the parlor build - the back would was just like a potato chip. Here it is after the braces were first glued on



I chiseled them off and let the plate stabilize at 40 percent for a couple of weeks



New braces with a 15 foot radius clamped against a caul with the same curve



Much better now



However, this is also the guitar that cracked when I took it back in to a 20 percent RH room, so there may still have been some problems.

Jan 09, 10 | 8:09 am
Ken Cierp

Total Topics: 58
Total Posts: 2262
Did you contour radius the braces yourself?

Ken

Jan 09, 10 | 8:11 am
enalnitram (Martin Lane)

Total Topics: 47
Total Posts: 332
Is that question for me or Ken? I purchased mine as part of a kit. Some of my braces were radiused and some weren't, so I radiused the ones that weren't.

Jan 09, 10 | 8:45 am
enalnitram (Martin Lane)

Total Topics: 47
Total Posts: 332
Also, Ken, if "a top or back that was dried to 6% or so will acclimate to the room in less than 24 hours" then mine maybe wasn't, unless I'm missing something. It stayed stable for 4 months and then began to move.

But then it's also a possibility that my room changed drastically without my being aware that it had.

Jan 09, 10 | 8:49 am
Ken Cierp

Total Topics: 58
Total Posts: 2262
I assume you used some kind of contoured clamping caul when you glued on the bracing correct? Also, just because the bracing had a 25' radius does not mean it had the stiffnes to shape the top to that degree --- if the top or back was too thick (how thick are they) they surely will flatten with the plates when removed from the cauls and gluing clamp.

If this stuff has been in the same room for all that time -- surely the actual humidity the days you glued things up versus actual current humidity has a lot to do with what you are seeing.

Ken


Jan 09, 10 | 9:58 am
Ken Cierp

Total Topics: 58
Total Posts: 2262
This is sort of a side bar to your issue --- but I stopped using the 3/8" H x 3/4" W -- back braces over 25 years ago because of problems with them wanting to flatten out/bow on the vertical no matter how perfectly they were split or sawn. I now use 5/8" H x 3/8" W all the time. Maybe I just had bad luck or did not know what the heck I was doing?

Ken

Kenneth Michael Guitars est. 1978

Jan 09, 10 | 12:37 pm
Bill Cory

Total Topics: 158
Total Posts: 3584
Ditto on the humidity issue. I recently put a spruce top on, left it in a cold garage too long, and it reversed from about a 28' outward arch when glued, to about a 28' inward arch. I made a humidifier, stuck it inside, closed the soundhole and put it in a hmidified room. Now, it's back to the arch it shoulda had from the start.

Bill

Jan 09, 10 | 1:05 pm
Tony_in_NYC

Total Topics: 29
Total Posts: 448
Bill....the spruce basically reversed its arch and did not crack? Thats amazing! It was glued on to a rim at the time, right?
Damn. I would have thought it would crack before being able to bow the other way like that.
Sorry...I had nothing to add to the discussion. I just had to comment on Bill's magical reversing top. Patent that top and sell it to Taylor or someone! Bill Cory's Inverting Brace pattern.

Jan 09, 10 | 5:21 pm
enalnitram (Martin Lane)

Total Topics: 47
Total Posts: 332
I hadn't thought about laying a straight edge on the top and taking a picture that way. It's concave -- kinda too embarrassed to post it anyhow.

Now that I've gone back over everything and done some exploration on the topic, I'm convinced regarding what happened. I received a gorgeous top and back. I glued bracing to it in November. Then, a few months later (with not much activity happening in the build) the humidity dropped in my house, and the top and back shrank. Luckily it wasn't glued to the sides when it happened.

(Is it true that african mahogany moves quite a bit more than spruce or rosewood?)

I've been told a solution would be to remove the bracing now and build while it's dry, and that future swelling won't cause as much problems as drying. if it's all the way dry now, and I build now, it won't crack due to dry conditions. Is this wise?

Or I could leave it all together, and get humidity up to 40% rh in my shop, and then resume building. Or just wait until March.


Jan 13, 10 | 6:52 am
enalnitram (Martin Lane)

Total Topics: 47
Total Posts: 332
What I wound up doing was:

remove all the top and back bracing
remake the bracing using nice wood I got from John Hall
let the bracing acclimate while I monitored RH
glued on top and back bracing after RH had hovered in the low 40's for a few weeks.

While I was getting into it, taking off the bracing with a plane, and then a chisel, it felt like what I was doing was a monumental chore. but in retrospect it wasn't a big deal. I had all off in about a half a day. Getting the chance to re-do the bracing made it better. I voiced the second set better than I did the first.

It was also fun making my own bracing. That's another thing that I thought was going to be hard, but that also wasn't a big deal at all. If you have a table saw, and an accurate way to make the radii, then you're all set.

Here's the top after I had removed the old bracing and had glued on the new "X". I was able to keep it clean by using small diagonal chisel strokes. going diagonally is the key.





Here's how it looked after the re-do.





I forgot to take a pic of my popsicle brace alternative, until after the top was glued on.



Mar 24, 10 | 6:43 am
enalnitram (Martin Lane)

Total Topics: 47
Total Posts: 332
Oh yeah, I also forgot to take a pic of the cap I put on the center of the "X" until after the top was on, also.

In the pic you can see the $1.49 Walmart brown cloth ribbon I used for the sides...

http://4.bp.blogspot.com/_En-9Zy8jJW8/S6aqVtCdbFI/AAAAAAAABL0/eMwz_uXlvoU/s1600/IMG_4576.JPG


Mar 24, 10 | 6:47 am



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