Straighten Bowed Top

[wwood]

Hi,

I've got a 3/4" bookmatched set of flamed maple which is ready to be joined and glued to the back

Both pieces have a slight bow in them across the width.

I've tried to straighten them by dampening them and resting heavy items on them and it has slightly improved.

I'm sure with enough weight and clamping at glue time I can just force them flush with the back of the guitar but was wondering if anyone had any practical solution to cure the bow?

Thanks

ww

[Mattia]

Glue up as close to flat as possible, sand/plane/flatten the gluing surface once they're together. Or flatten, then glue, although there's a slight risk it'll move again at that point.

How much of a 'gap' are we talking here, laying the pieces flat with the cupped side down? Because while flattening a 1/4" top by clamping is a relatively trivial exercise, a 3/4" top is a different matter. The only thick top I ever 'forced' into place and glue was a carved top, in and out, no more than 1/4" thick for most of it, and I had to correct for about 1/8" of an inch. Was my first. These days, I'd have tried getting it flatter before gluing. It's holding up fine now, mind you, 8 years on.

[wwood]

Thanks for the reply mattia.

When laid down flat on the cupped side the gap is approx 1/16" on each of the halves.

I'd be much happier to get them flatter before joining them otherwise I think it may be best to join and glue them to the back all at the same time using clamps and heavy downward pressure (i.e. heavy weights)

This sound like the best option to you?

Regards

ww

[Mattia]

1/16" is very, very little, and your system would work. You can flatten them now (by sanding), then join, then cut the shape out, but what I do in these cases (because I have to flatten stuff like this by hand, on a flat surface with some sandpaper since my handplanes do not like highly figured wood) is get a good, solid join (if that's not working, I'm forced to flatten the pieces first), glue it up, cut out the body shape, and then flatten the piece you've cut out. This minimizes the surface area you actually need to sand flat, see?

[fryovanni]

It would be best to flatten the top before you try to join it. If you have two cupped boards it will be hard to get the joint tight. If you apply pressure and hold one board to a flat surface, and then try to join the second you will have an odd angle on the two joined surfaces. If you force the second board flat then try to force the two flattened pieces together they may or may not get forced together correctly. You would be money ahead to try one more time to flatten them. Let them sit for a litlle bit(stabalize). Then check them again and flatten the backs(hopefully they will be very, very close at that point). After they are flat double check the joint and be sure the two surfaces meet correctly(straight and square). This is more about getting a good looking (and tight joint). If you just want the boards to stay attached to the body you could probably press them on and they would never let go(but it is going to be difficult to get a clean joint). Just my 2 cents.

Peace,Rich

[Guitarfrenzy]

This warping or cupping of the wood is exactly why most people who have quite a bit of guitar wood buy them in billet sizes. If you resaw them to 1" or under your taking the chance that your wood won't stay level after a couple of weeks. That's why when you buy wood at that thickness, you need to go ahead and use it before you have problems. If your going to keep the wood around for a while before you use it, it's best to buy in billet sizes to eliminate this problem. Sounds like your on the right track and are going to get this guitar started before it's too late though. Good luck with your project.

[wwood]

Thanks all for your replies.

I'm gonna' spend another couple of days trying to press out the bow, hopefully that should see to it, but if not then I'll work it down to as flat a surface as I can by sanding as the bow isn't extreme enough to go at it with the trusty plane.

The back is thickness ready so I'm good to go when happy with the top.

I just flicked through a couple of books for some advice and noticed that Melvyn Hiscock had a similar problem when building his Tele (although it only had a 1/4" top...page 108 if anyone's interested)

He jointed and glued the top to the back at the same time so this approach may pay-off if I can't reduce the bow any further.

The piece was originally 3" thick and I had 2" re-sawn, split and thicknessed. The bow appeared pretty much the day after. I can only summize that it was either originally stacked badly or not dried out enough.

I'll keep you posted on my efforts, this is hopefully going to result in a lovely carved top in the coming weeks.

Thanks again to all, your advice has been helpful and re-assuring.

Regards

ww

[Mattia]

Did you sticker and weight it immediately after resawing?

Once wood's stable, it's stable-I'd be fairly wary of using freshly resawn pieces from billet form, and prefer to have tops milled to spec, to where I need them to be a while before I use them. Then sticker and weight and let everything acclimatize. Because honestly, if it's going to move, I want to know before I glue it to something. Thinner stock moves, but that's what stickering is for. I've got plenty of the stuff, and yeah, I'd keep it in billets more for the flexibility (is it going to be a thick top, drop top, something in between-top?) than for stability's sake.

Edited February 9, 2006 by mattia

[fryovanni]

Did you sticker and weight it immediately after resawing?

Once wood's stable, it's stable-I'd be fairly wary of using freshly resawn pieces from billet form, and prefer to have tops milled to spec, to where I need them to be a while before I use them. Then sticker and weight and let everything acclimatize. Because honestly, if it's going to move, I want to know before I glue it to something. Thinner stock moves, but that's what stickering is for. I've got plenty of the stuff, and yeah, I'd keep it in billets more for the flexibility (is it going to be a thick top, drop top, something in between-top?) than for stability's sake.

I couldn't agree more with what Mattia is saying. I have a theory(and it is just that) that the heat produced by the re-saw blade especially on harder woods will tend to create a temporary imbalance in the mosture levels. I believe the effect only last for a day or two then equals back out. Now if the wood was not really dried well or evenly (especially on thick and oily woods) it will keep on moving for a while(really not the effect of blade heat). In those situations you should allow enough time for it to finish its drying process. If you plane or surface it will not stay true. I am basing this all on my experience, so just take it as my opinion.

Peace,Rich

P.S. If you are going to use thicker billets and re-saw them. Get a moisture meter and test it before you cut (so you know what you are going to be dealing with). It can be hard to read moisture levels on wood thicker than 2" accurately, but it shouold give you a good idea of it's state.