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How would you flatten this top prior to joining and bracing?
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Author:  David J Fisher [ Thu May 05, 2016 6:00 pm ]
Post subject:  How would you flatten this top prior to joining and bracing?
Greetings. I apologize for the poor image quality. My poor old beat up iPhone seems to have its camera packed with sawdust/pocket lint. But hopefully you can see enough of what I'm up against here. I've got a hardline or compression 2nd growth red spruce top. Its is particularly feisty and stiff. I'm quite fond of it, however its got a strange cup end to end, and twist side to side. I've tried heating the convex side with a head gun. I also left it clamped between my spindle sander and goobar deck for a few weeks. Nothing. I'm hesitant to introduce moisture at this stage in the game. I've got a box ready for a top. The top is at .165" at its thinnest spot and around .175" average. I know most people probably wouldn't use it. I'm pretty attached to it, and am going to attempt to join and brace it once its back to flat. I've also thought a fixture could be made to keep the pieces flat while edge jointing and glueing the top together and then brace it. Kind of like the LMI Obrien plate joining jig. I've never used a fixture like this and it doesn't seem like it would work very well with hide glue. Maybe I'm completely off base on that assumption. Anyway, any ideas are greatly appreciated. I've got lots of other tops I could use, and it may come to that, but I'm going to give this one the old college try.


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Author:  Clinchriver [ Thu May 05, 2016 6:10 pm ]
Post subject:  Re: How would you flatten this top prior to joining and brac
I would glue it up and then see what it was doing at final thickness, what size guitar?
Author:  David J Fisher [ Thu May 05, 2016 6:16 pm ]
Post subject:  Re: How would you flatten this top prior to joining and brac
Thats kind of the direction I was thinking makes the most sense. The guitar will be a dread with padauk back and sides. Thanks
Author:  Clinchriver [ Thu May 05, 2016 7:13 pm ]
Post subject:  Re: How would you flatten this top prior to joining and brac
David J Fisher wrote:
Thats kind of the direction I was thinking makes the most sense. The guitar will be a dread with padauk back and sides. Thanks


So somewhere between .110 & .120 for good Red Spruce, hopefully the "best" side will let you brace to the curve in the top good luck.
Author:  David Newton [ Thu May 05, 2016 9:13 pm ]
Post subject:  Re: How would you flatten this top prior to joining and brac
You didn't say exactly how long it has been in your shop. ?
If it has been a year, I would join it and use it. I think if you thickness it to .120" you will be able to brace the warps out and it will be fine, and may surprise you, I hope!
Author:  David J Fisher [ Thu May 05, 2016 11:10 pm ]
Post subject:  Re: How would you flatten this top prior to joining and brac
The top has been in my shop at 35-40% RH for about 4 months. It was cut in 2013. Im still not certain the best way to approach jointing and joining the warped plates. I would assume that for an accurate joint, they must be pressed flat before the edge joint is established. I would then also think the plates must be joined and glued whilst being held flat. Maybe I'm over thinking this. My way of gluing plates is to use the go bar deck to press down on the and wedges to drive the plates together. I don't reckon that would be sufficient in this instance. It seems as though it wants to be sandwiched between known flats in both jointing and joining. Thanks for the input.
Author:  Joe Beaver [ Fri May 06, 2016 1:33 am ]
Post subject:  Re: How would you flatten this top prior to joining and brac
I would just put it in a sandwich of two flat pieces of wood for shooting the joint (probably the hardest part of making a good joint with warped wood) and then put some clamps down on the work table, lay some 3/4 or so plywood, a little narrower than the joined pieces, some wax or parchment paper, the prepared top halves, more paper, another piece of ply and a lot of weight on top then clamp.

I won't be perfect but with .165 it should sand out nice.

Put a rosette in, finish sanding and brace it. It might be fine.
Author:  kencierp [ Fri May 06, 2016 8:40 am ]
Post subject:  Re: How would you flatten this top prior to joining and brac
I agree with Joe's idea of putting the plates in a sandwich for truing the edges. Our set up for gluing the plates together takes this problem into consideration -- the joint clamping caul is bowed in the center so that pressure is applied along the entire seam as the end clamps are tightened.

http://www.kennethmichaelguitars.com/Jo ... alves.html
Author:  mflazar [ Fri May 06, 2016 8:56 am ]
Post subject:  Re: How would you flatten this top prior to joining and brac
Try wiping it down with a damp cloth on the concave side only. Don't get it too wet. Let it sit on a bench concave side down. It may straighten in a few minutes and stay that way long enough to joint it. That being said, I think the previous suggestions are all good. Once you get it joined, you might want to use the dampening process on the concave side to keep it straight while thicknessing. Once it is thicknessed if you are bracing it in a radiused dish I'm sure it will end up just fine.
Author:  Bobc [ Fri May 06, 2016 9:02 am ]
Post subject:  Re: How would you flatten this top prior to joining and brac
I would try removing some of that excess material around that knot. Make a nice straight cut untill you get to the lower bout and you should be able to clamp or wedge the two different widths. I have a feeling that the knot is causing some of the problem.
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