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Hello everyone -
I've been experimenting with Hot Hide Glue on my nect build - a Koa OOO-sized steel string, to mostly good results. I really like using this glue and actually find the fast set time to have some advantages and love the easy cleanup with hot water. It also appeals to me to be using a "tried and true" technique.
I've bumped into one challenge - I've used HHG to join my Sitka Spruce top, and although it's a pretty clean joint, without much like shining through, after it's set and I've scraped the residue, there remains a clear darker line down the top, right along the seam. I'd say it's just the color of the glue ,which is considerably darker than the Sitka.
So... how does one avoid this - it's clearly purely an aesthetic issue, but even so -

Thanks!!

I don't think it's purely an aesthetic issue. I think it's a jointing issue. If the joint was super tight there would be no dark line. I only use HHG and I get no lines, as have thousands of guitars before me.

Tell use more about your jointing, and clamping/gluing up process. That is where the issue is.

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John Mayes
http://www.mayesluthier.com

It's not aesthetic. The joint will fail. Any HHG joint, especialy a top or back seam should be invisable. Either the joint didn't fit tight enough(which probably isn't the case) or the glue cooled enough to gel before the joint was clamped/pulled together. I always heat the pieces I'm gluing to give me a little more open time.

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Thanks!! I appreciate it - I'll work on 1) making sure the joint is as close to perfect as I can, and 2) ensuring that the glue and pieces being glued are hot enough to prevent premature cooling.

This is your problem. You can not have ANY light shining through the joint. The joint must be perfect or you'll have issues, especially with HHG.

Tell us about your procedure, although I suspect that you will have to heat the joint, separate the plates, shoot the joint again, making sure it's perfect and glue again.

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You said without much light shining through. Even a hair of light is to much. You need to tighten this joint up.

Also, if the glue is dark it's probably too old. The stuff deteriorates with age, and loses a lot of strength. You should mix up a fresh batch for doing the center seam. Glue's cheap, repairs are expensive.

I could sometimes see a discoloration in the area of the center seam with hide glue in a really pale wood like Lutz even if the joint seemed good. I sometimes wondered if I was using too much pressure clamping and compressing the fibers. Seems better since I went to the tape method and lighter pressure with wedges. Does that make any sense?
Terry

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Thanks all - I think my problem seems to be a combination of all three issues - poor joint, somewhat old glue (heated and cooled about half a dozen times, and yes, it's turning pretty dark, and the glue cooling too much before the joint is lined up perfectly. Not easy to keep the plates hot enough, they cool very fast.

Rod, here's the technique I'm using - and I do seem to have trouble getting the joint perfect - frequently a very gradual convex surface - when I put the plates together to test the joint, they're toghether in the middle and showing daylight at both ends.

I have a long straight shelf that is covered with formica that I use as the base of my shooting board. It's straight and the plane slides on it easily due to the formica. On top of this I clamp a length of plywood, leaving sufficient space for the plane. The plywood is the foundation for the soundboard plates, which I stack (so that any angle imparted on the joint of the plates by the plane is the mirror image on each plate - e.g. plates glued together will be f180 degrees - flat.)

I clamp a straightedge over the plate, about 1/16 of an inch from the edge, as a guide, then shoot the plane along the edge of the plates, attempting to apply even, light pressure. I also try to work with a very sharp plane (I've tried both my Stanley planes - the 10 inch and the 14 inch - with similarly poor results).

Any help or advice very welcome. Clearly my technique is off somewhere - when I manage to get the plates perfect, it's much more a matter of luck (infinite number of monkeys at keyboards) than through good technique.

Unless I missed it one issue not mentioned is cleanliness of the glue. Especially if it is reheated and rejoined. Any dust in the glue or the joint will cause either a slight gap in the joint or debris in the glue.

I use to use a block plane to shoot my boards before I got a real plane. It took time and care to get the joint right but it's possible.

Your shooting board sounds fine to me. Here's one thing I do when looking at the edge after I shoot it. I notice where the gap starts (either at the ends or in the middle) and I mark that point with a pencil line. On my neck shoot, I plane the high section only, taking a very lite pass. Than I check again. I work this way till I get the joint perfect.

I've changed my shooting board set up now though. Instead of moving the plane, I move the boards. I always seem to get gaps at the ends of my plates which shows me I put to much pressure on one end of the plane. So, I clamp the plane to my bench, I set up a board in front of it (the board is flat and about 2x's the length of the plane) attached with double sided tape and I run the boards through the plane. I find I get better results this way.

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"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

Crokey, would a setup like this help you?........

http://www.luthiersuppliers.com/products/p11.html

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Formerly known as Adaboy.......

Thanks - great advice. I'll work on my technique.

A tip I learned years ago is to use an aluminum carpenters level. Stick sandpaper to the narrow sides (one grit each side) stack the boards so one hangs slightly out over the other and sand it flat. Re-stack with the other board on top and slightly overhanging, then give it a go.
Art