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Center seam separation in thicknessed Western Red Cedar Top

PostPosted: Wed Jun 12, 2019 7:50 pm
by Kristoffer Ross
Good afternoon, everyone!
I need some advice on whether to go forward with the WRC top I have (almost) thicknessed, or whether I should play it safe and order, joint, and thickness another.
For one reason or another, I haven't had time to get back to my first guitar in the last month or so, since getting the plates jointed and close to final thickness. When I looked at the top today, I found there is some seam separation along the last 2 1/8" of the upper bout. In most of the space, the Tightbond I is still bridging the gap, but at two pinprick-size points within the outline it's just air. Since all this will be under the fretboard, is this a structural issue?
Also, when I test-tap letting it hang by thumb and forefinger, I can hear a very slight rattle from that area. The noise doesn't occur when I hold the top by the edges with hand and shoulder*. Perhaps this will go away when I trim off the 1/2" of waste, where separation is worst. Do you think that likely?
Many thanks,
~Kristoffer
SAM_0035 (600x450).jpg
General shot of the top (with my shop decor in the background:-).

SAM_0044 (600x450).jpg
Here you can see the scale, and the transparency of the Tightbond I where it has separated. From the pencil line to the edge is waste.

*Note on thickness: I have the top at to about 9/64ths currently - The Cumpiano Book, which I am following, calls for 7/64ths if using spruce. I'm thinking I should go to an even 1/8th with the weaker cedar. Does this sound prudent?
*The main tap tone is different here too: Holding the edges seems to ring an octave higher than letting it hang.

Re: Center seam separation in thicknessed Western Red Cedar Top

PostPosted: Thu Jun 13, 2019 1:17 am
by Peter Wilcox
I am certainly no expert, but I would say there should be no problem. Cosmetically it will be under the fret board, and structurally it will lie over and be glued to the neck block, and maybe even cut away if you're planning on a mortise and tenon neck attachment. That should alleviate any sonic issues you're concerned about.

Re: Center seam separation in thicknessed Western Red Cedar Top

PostPosted: Thu Jun 13, 2019 11:08 am
by Barry Daniels
This is a weak spot (obviously) and it may lead to the whole joint failing unless you do something now to reinforce it. I would open it up by running a small backsaw though the open part of the joint and then glue in a splint.

The way the joint is open, I would guess that you do not build with any control of your humidity. You might want to do some research on that topic.

Re: Center seam separation in thicknessed Western Red Cedar Top

PostPosted: Thu Jun 13, 2019 4:51 pm
by Kristoffer Ross
Thank you both for your input.
Barry, the splint idea sounds just the ticket, I will proceed with that. Yes, I don't have the ability to control humidity at all in the workshop, though I keep my workpieces at a small bench in my bedroom between sessions and during curing periods. The workshop is an old 12x16 grainery that was sided over for use as an antiques barn, which I have taken over half of. In the fall I may be able to peel the clapboards off, sheath and insulate it, but for now it's quite basic and prone to Northeast humidity fluctuations.
Best,
~Kristoffer

Re: Center seam separation in thicknessed Western Red Cedar Top

PostPosted: Fri Jun 14, 2019 11:52 am
by Clay Schaeffer
I would leave the Cedar at 9/64ths - the final sanding will remove some material and you want to allow for that. You may want to make a drying box for your guitar parts. there should be information in the archives.
Much of the center seam of the top is either covered or gut away (soundhole) so it is the lower bout that is most important to be well glued. Some people put small cleats in that area. On a fan braced guitar the center fan usually covers it.
Good luck with your project.

Re: Center seam separation in thicknessed Western Red Cedar Top

PostPosted: Mon Jun 24, 2019 9:29 pm
by Kristoffer Ross
Thank you Clay, I will look into the drying box. The lower bout is in good shape, and I plan to put two cleats in it anyway.
Best,
~Kristoffer