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Gobar and Tape - Back Join
http://www-.luthiersforum.com/forum/viewtopic.php?f=10102&t=4937		 Page 1 of 1
Author:  Bruce Dickey [ Mon Feb 06, 2006 7:22 am ]
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Different take on a couple of methods. I had a tented glue up grab too quickly, causing misalignment of the two backpieces. So, I went back to the gobar for an attempt at combining the two methods.

The added hardwood strip traps one side flat against the wax paper and disallows movement. The second side is installed carrying the glue to the joint. It is gently slid back and forth and aligned.

Installation of the second hardwood strip and a couple gosticks at the ends, then allow application of the tape strips, without the second set of gosticks in the way. The final gobars are added and as you can see, a nice beading of glue is forced from the joint for later cleanup.

I used to do this a lot, but always put the hardwood strip over a second piece if wax paper. That spread glue all over, so this open setup might be better in that regard. For your amusement, we'll see how the joint turns out.
Author:  crich [ Mon Feb 06, 2006 3:08 pm ]
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Did you use white glue? Maybe a dumb question but I was going to use yellow or hide glue. Clinton
Author:  David Collins [ Mon Feb 06, 2006 5:45 pm ]
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It looks good, but I guess I still prefer a couple sticks and rope.
Author:  klhoush [ Mon Feb 06, 2006 6:05 pm ]
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[QUOTE=crich] Did you use white glue? Maybe a dumb question but I was going to use yellow or hide glue. Clinton[/QUOTE]

It's probably instrument makers glue.

Kurt
Author:  Bruce Dickey [ Tue Feb 07, 2006 12:24 am ]
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Glue is White Titebond, But it was the method I was sharing. I'll go take it out and see how she worked overnight. Never got back to it to scrape off the glue.



Looks like it worked well, very even join, two passes in the drum sander cleared the joint, the other side had a bit of stairstep due to varying back thickness and it took about five passes. It's still way thick at .130" I'm not fond of sapwood in this Leopardwood species, but the stock isn't wide enough for a jumbo without it. I knocked the dried glue beads off with a scraper before hitting the drum sander.Bruce Dickey38755.4186458333
Author:  Michael Dale Payne [ Tue Feb 07, 2006 2:25 am ]
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Hummm? What I did not get from your explanation is how pressure is exerted to mate the two haves toward each other. I may have missed it, but I did not get that from your post

With out a force pressing the halves toward each other, I would worry about surface tension of the glue causing the two halves to appear flush butted, actually having a micro separation.

Tenting method, rope and wedge method and vice method all force the two halves toward each other under tension. I just don't see this here.

Please explain
Author:  Mattia Valente [ Tue Feb 07, 2006 2:56 am ]
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Michael, I think he's using the 'strechy tape' joining method many here advocate for tops, and has the go-bars in place to keep things lined up as an alternative to weighting.
Author:  Michael Dale Payne [ Tue Feb 07, 2006 2:58 am ]
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right before my eyes and I missed it Thanks Mattia
Author:  Bruce Dickey [ Tue Feb 07, 2006 5:13 am ]
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Mattia got it. I would use the tape alone and have. What happened recently on a top was the White glue grabbed so quickly, it didn't allow me to align the two halves flat. That caused me to go back to the gobar deck, my old method.

So in this model you 1. Pin the first half in position with the gobar. 2. Slide the second half in position, with a rubbed joint. The hand action basically does it all. 3. Then two gosticks are applied at the ends, leaving the center open for application of the tape. 4. Tape application pulls the two back pieces together. 5. Install the remaining gosticks to level any joint unevenness.

Basically the joint is made at the end of step 2. the glue pops up in beads, very little glue flattens out on the back of the joint. It is also an attempt to keep the bookmatch face, which is down, to require as little sanding as possible. All subsequent excess stock removal is done from the inside of the material retaining the bookmatch as much as possible. There my have been .005-.010 variance of the stock, which is removed when dry levelling the inside nicely.

The joint looked good as you an see from the picture. It took a good sanding and some CA filling on two sapwood pinholes. Ready for some braces and profiling.
Author:  Cocephus [ Tue Feb 07, 2006 5:58 am ]
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Here`s the way I do my joining. I did use the idea that I read on a post in the past. Thanks whomever you were!
Nice and simple. I`m getting the impression that we`re reading too much into joining tops and backs, IMHO. If you get a good joint and make sure you`re satisfied with the candle test, you should get a practically invisible joint line. I set my edge stops up just a tad closer than the pieces being joined, glue, match, and press. Weight it down, and there you go. In the pic, I moved my weights to the ends to show the joint.
Author:  Dave Rector [ Tue Feb 07, 2006 9:23 am ]
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I do it exactly like Cocephus does except I just throw a bag of shot on top.
Author:  Bruce Dickey [ Tue Feb 07, 2006 9:37 am ]
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I did have a thought and it applies to Dave and Cocephus's added weight and my gobars. The joint is pinned immovable. Doesn't the joint shrink causing it to pull apart? Huh?

No, it doesn't, here's why. The wood at the joint is taking on moisture and swelling actually. A minor ammount i'm sure. But probably just enough to allow for shrinkage in the joint with no separation.

You sometimes have to think like wood fiber to understand the mysteries of life.
Author:  Michael Dale Payne [ Tue Feb 07, 2006 11:37 am ]
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[QUOTE=Bruce Dickey]
You sometimes have to think like wood fiber to understand the mysteries of life. [/QUOTE]

If I did that Bruce i would be up in flames in a flash
Author:  Serge Poirier [ Tue Feb 07, 2006 3:27 pm ]
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Ok now ,rookie here wants to know which of Bruce's or Coe's is the best way to go? Nah, just kiddin' as usual! Wouldn't want any glue thrown in me face

Both methods are easy to understand and apple eye!

Thanks for the tips fellows

Serge
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