Center seam separation- disaster?

[Bill Hicklin]

Doing a maple archtop back, I got the top face rough-carved and had most of the inside hogged out when I saw to my horror that the center glue seam has a hairline separation from the bottom edge up about 2 or 2-1/2"- even though I spend a great deal of time getting the mating faces perfect, and let it dry for over a week before I started carving.

What now? I can hardly cut it apart and re-glue, with the carving in such an advanced state. Glue + clamping force strikes me as a Bad Idea. Some sort of paper-thin fillet?

[Michael Lewis]

What kind of glue did you use?

Likely your wood may be not as well seasoned (dry) as would be optimum, and it can distort a bit as it dries as you uncover new surface deeper in the piece.

You can reinforce the area with cleats or a reinforcing strip like in most flat top guitars use along the back seam. If you used hide glue you can put more glue in the seam but only after you hydrate the back so the seam closes.

[Greg Martin]

Im in Colorado and the same thing happened to me, after pondering weather to keep going, reinforce and hope the customer doesn't have a problem down the line. I couldn't do it. I heated the back off the rims and searched for new new back, to start again. if it had been my own id have continued on, thinking it was a test and see if it would stand the test of time. It wont though !!! Note I did use titebond II. Maybe that was the problem, or seasoning or lack of.

[Michael Lewis]

The glue you use will not cause the back to shrink, which is what causes seams to open. You may be able to reuse the back if you remove the braces, dry it thoroughly, and put it back together. You may need slightly larger bindings or purflings to cover everything that has been opened.

[Greg Martin]

I tried to save the back today , I separated it with a heat gun made a couple of impromptu jigs to use a shooting board to re true the halfs the joint is good, but without making a detailed glue up jig to align the arches along the length I think it will be difficult to get and keep a perfect glued joint putting me exactly where Iam now.
My lesson is this, no rushing. A good joint on a cabinet or table may not be a perfect joint on an archtop .
An expensive learning experience. one other thing. just because a back has awesome grain and the seller says it dry and ready, my feeling is its not yet ready to use. Im going to buy material this year, season it for use in a year or two.I wont be making as many as the pros here but good wood is nice to have anyway. I do have seasoned material for one more 17",material Ive had for over ten years but I cant use that on this build, its spoken for. Yep Live on and learn every day. Let the fun begin !

[Michael Lewis]

There is a whole lot of education in this particular issue as many if not most folks that have made archtops (also mandolins, violins,) have had direct experience with. We all expect our materials to be good and ready for working, but the truth is we really need to check the condition of the wood before working it. For those with moisture meters the problem is fairly easy, just run the meter over the wood and look at the display, but for those without such a device you need to have access to an accurate scale that measures in grams and parts of grams. Just weigh the wood when you get it and write the date and weight on the wood, then in a week or a month do it again. As long as the wood gets lighter each time it isn't ready to be worked.

When a seam opens you are faced with a 'repair' issue. The idea is to get it closed and reinforced, or disassembled and refitted and glued. This can be a difficult problem if the wood isn't properly seasoned, because it will continue moving as it loses moisture. Make it stable before repairing it or you will likely have to do it again.

One danger is flexing the seam near the edge (tail block and neck block areas) where the wood can be rather thin and flexible. You NEED a carving cradle to support the edges all round for both outside and inside as you carve the plate. I use a piece of MDF or 3/4" plywood about an inch bigger than the outline of the plate with some thin blocks or a 'ring' glued to the base material to form a ledge that captures the plates. This ring should be no thicker than the edge of the plate you are carving. Cut out in the inside of the base material so the outside arch can hang in thin air when the plate is inside up with the edges firmly resting in the cradle ledge. For a cutaway model this is a double sided 'tool', so you can flip a plate to carve either inside or outside, top or back. For a 'full body' with no cutaway you only need one side fitted to the plates because they are symmetrical outside edges inside and out. By using the cradle you avoid risking flexing the seam and it really helps to hold the plate securely while you are hogging material away.

[Greg McKnight]

Michael, would it be a lot of trouble to post some pics of your carving cradle? I haven't made mine yet and would value another look at someone else's.

[Patrick Hanna]

Greg, I just happened to click in and saw your request for carving cradle photos. I don't know how helpful this will be, but it might give you a few ideas. This cradle is made from three layers of plywood scraps. The bottom layer is solid and the other two layers have been cut to a shape that is about 1/4-inch smaller than the guitar perimeter all around. I have cork-padded clamps at either end. They have slightly over-sized holes which slide down over bolts. Then clamping knobs thread onto the bolts. The bolts slide up from the underside of the fixture. I use shorter bolts for clamping a top or back and longer bolts for clamping an assembled box. The end clamps have half dowels glued across their tails. These act as fulcrums when the clamps are tightened down. When I want to work in the neck or tail area, I just remove these clamps and use padded c-clamps along the sides of the fixture. A pipe flange is screwed to the underside of the bottom and a length of 3-inch black pipe is screwed into the flange. This allows me to pivot my cradle as I work. I'll explain that in a follow up post.

[Patrick Hanna]

There is nothing fancy about my pivot clamp. I'm lucky to have this big old front vise on my bench. I glued up several layers of scrap pine with a 3-inch center hole pre-cut in each layer. My top layer is over-sized so it can rest on top of the vise jaws without falling through. It would work even better if it also overlapped the moving jaw of the vise. Note that the hole is cut off center so the pipe can clear the ways of the vise. I sawed a gap through this fixture from one edge, through the hole and part way into the other side. The pipe on the bottom of my cradle slides down into the hole--just clearing the vise way--and the flange rests on top of this fixture. You can see that the fixture has been burnished by the flange as I continually pivot the cradle. The front vise closes this clamp on the pipe, locking the entire fixture in place. I can back off the vise pressure, spin the cradle to a new position and reclamp it in just a few seconds. It takes longer to put down my plane and pick it back up than to re-position the cradle. Nothing fancy, but it sure gets the job done. I hope this has been somewhat helpful.

[Greg McKnight]

Thanks Patrick! That is very helpful indeed.

[Michael Lewis]

Greg, I can e-mail a couple pics to you if I could have your e-mail address. Posting pics is a bit more computer complicated than my sleep deprived brain wants to handle right now.

[Greg McKnight]

Greg, I can e-mail a couple pics to you if I could have your e-mail address. Posting pics is a bit more computer complicated than my sleep deprived brain wants to handle right now.

So I'm not the only one that isn't well rested huh? That makes me feel a little better.

pm sent, and thanks for the offer.