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perfect rib seam at tailblock

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perfect rib seam at tailblock

Postby Sandy Winters » Thu May 26, 2016 8:05 am

I've never paid too much attention to perfect rib seams at the tail/bottom of my acoustics because I have always inlaid binding/purfling at that seam. I have a customer who wants me to build a Gibson J45 'clone' and wants the seam at the bottom to be just like Gibson (or Martin, for that matter).....no inlay.

I'm sure that with a bit of careful handwork I can get a perfect seam at that joint but I am wondering if anyone here at the forum knows how Gibson or Martin **used** to accomplish that perfect seam (I'm sure everything is done with CNC control now). I can't imagine they would spend a lot of careful handwork at that procedure. They must have had a relatively sophisticated fixturing system of matching the seam and then holding in place while clamping.

Any thoughts, or direct knowledge?? Thanks
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Re: perfect rib seam at tailblock

Postby Rodger Knox » Thu May 26, 2016 12:22 pm

Sandy Winters wrote:I've never paid too much attention to perfect rib seams at the tail/bottom of my acoustics because I have always inlaid binding/purfling at that seam.
Any thoughts, or direct knowledge?? Thanks


I also usually inlay at the tail, but it's really not too difficult to get that seam perfect without any extra jigs or fixtures, just use an outside mold and get the seam tight when you glue on the tailblock.
A man hears what he wants to hear, and disreguards the rest. Paul Simon
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Re: perfect rib seam at tailblock

Postby Ryan Mazzocco » Thu May 26, 2016 7:08 pm

I've also never done this for the same reason you mentioned, Sandy. But I have thought about it quite a bit as I have been talking with a potential customer that wants the same thing. Here's what I was thinking.
I normally use an outside mold and glue the headblock, tailblock and both sides (or ribs) all at the same time. But for something like this I would be worried that the outside mold would limit my visibility and I wouldn't be sure I was getting a perfect joint. My idea is this: After bending the sides and prepping the tail block mark the exact center of the tailblock and make a line perfectly square to the top (the surface to which your top plate will glue.) Make sure the ends of your sides are also perfectly square to what will be the top edge. Temporarily clamp (maybe using some spring clamps) one side to the tailblock making sure to line u the edge with the square center line. Mark the inside of the side where the tailblock ends. Now do the same with the other side making sure your joint is perfect while everything is dry. Mark that side also. Now remove the clamps. Apply glue to the inside of one of the sides from the end up to your pencil mark and carefully clamp it to the tailblock making sure the edge is perfectly aligned with your center line. Once it is secure you can go on to the other side. Apply glue to the other side and use some strong tape to pull it tight to the other side closing the joint, then clamp.
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Re: perfect rib seam at tailblock

Postby Chuck Tweedy » Thu May 26, 2016 8:09 pm

The other thing to consider is that this is an endgrain-to-endgrain joint, so you want to use a glue that is going to give the most natural possible glue line.
AND you do not want an adhesive that wicks into the endgrain and discolors it.

Hide glue pretty much fits this bill - tho it may wick in and discolor a bit.
Anyone have ideas on that?
The endgrain could be sealed to stop wicking - thinking out loud here.
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Re: perfect rib seam at tailblock

Postby Barry Daniels » Thu May 26, 2016 9:54 pm

That might be a factor for mahogany, but rosewood shouldn't discolor.
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Re: perfect rib seam at tailblock

Postby Randy Roberts » Thu May 26, 2016 10:03 pm

a couple quick wipes with shellac should prevent any wicking. It sure makes a maple miter or butt joint invisible even with thin CA.

How about this for the join:
Take a spare tailblock, cut a slot in it vertically with the bandsaw at a 90 degree to the outer face of the block so you can run a strip of sandpaper vertically in the slot and butt the sides up near each other and "floss" the "butting face" of the side so it matches the other side's "butting face" by sliding the sandpaper up and down in the slot? Maybe glue a sheet of sandpaper to stiff plastic, or metal sheet for this so it doesn't round the edges?

The lack of visual when gluing the sides to the block would drive me nuts. Maybe glue the butts of the sides together first with piece of paper on the outside face to reinforce and maintain alignment, and then glue up to the tail block in the mold? Sand off the paper later.

Like Chuck, just thinking out loud here, though I probably should be whispering.
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Re: perfect rib seam at tailblock

Postby Chuck Tweedy » Fri May 27, 2016 11:47 am

I like Randy's idea of pulling the joint together before trying to glue it to the block.
How about good 'ol tape??
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Re: perfect rib seam at tailblock

Postby Bryan Bear » Fri May 27, 2016 12:55 pm

I've never done this either but here is what I would try. I would get the sides bent and trimmed close to length at the tail. Then I would close the side up as if it were a bookmatched top (obviously the shape of bent sides will make it all floppy so I would tape or clamp the butt ends together best I could. Then I would joint the endgrain with a sharp block plane and some sort of improvised little shooting board. Once I was happy with the joint, I would wipe the endgrain with a couple dryish coats of shellac (wanting to stop the glue wicking in and realizing that I am not counting on the endgrain glue joint to carry much of the load).

For clamping, I would use something like the tape method for jointing plates. I would stretch some tape across the outside of the joint. Then apply glue to the tail block, position one side and clamp it to the block. Next I would re warm the other half of the tailblock to activate the glue and fold the other side over and clamp it to the tailblock. The stretch of the tape should close the joint uptight. Once it was set up, I would unclamp and put the assembly in the mold with spreaders and glue in the heel block.
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Re: perfect rib seam at tailblock

Postby Alan Carruth » Fri May 27, 2016 2:10 pm

I normally glue the end joint out of the outside mold. I put glue on one side and position it, then tape it in place on the block. I then pull the other side in to it with tape, secure it to the bloc with one or two lengths of tape, and clamp it with a caul. If the joint is smooth and tight it works perfectly.

Any water based glue will give a good tight joint in this application. CA or epoxy will not, because they don't shrink as they cure. You can't avoid the black line with them, or, at least, I haven't bee able to. There's no need to seal the end grain either, and it's probably better if you don't.
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Re: perfect rib seam at tailblock

Postby Clay Schaeffer » Sat May 28, 2016 7:55 am

To get a tight seam at the tail block I will tape the sides together on the outside, put the ribs in the outside mold, put a couple of thin shims between the mold and ribs (forcing the joint tight), and glue in the tail block with titebond. For shims I use formica scraps, but waxed wood or waxpaper between would also work - anything glue won't stick to.
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Re: perfect rib seam at tailblock

Postby Michael Lewis » Tue May 31, 2016 1:50 am

Late to the party again . . . .
I have done this for my archtop guitars and mandolins, and my method is reasonably foolproof. I glue the neck block to the sides first, when that is dry I overlap one side over the other at the end of the body. Here I make sure to clamp the sides firmly to the outside form so there are no gaps all round, and use a C clamp and small block at the tail as a fence to guide a razor saw to cut through both sides at the center line. Pretty simple and usually very clean.
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Re: perfect rib seam at tailblock

Postby Todd Stock » Tue May 31, 2016 4:57 am

Take care fitting the joint, then take care fitting tail block to curve. A bench hook and block plane work well together to get a square, tight joint. Tail block is clamped against mold (which has a piece of blue tape covering the seam for release should some glue go awry), and flexible spruce caul to clamp portions free of mold. Works well and the mold and bench top keep things square. I use 192g high clarity hot hide and never any discoloration on any of the woods I use.
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Re: perfect rib seam at tailblock

Postby Gordon Bellerose » Tue Jun 07, 2016 2:07 pm

If this is this a stupid question please forgive me.
Is it viable or even possible that the factory may bend one long piece for these guitars, thereby foregoing any seam?
I need your help. I can't possibly make all the mistakes myself!
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Re: perfect rib seam at tailblock

Postby Barry Daniels » Wed Jun 08, 2016 11:19 am

That has been done, but there is no advantage to it and there are several difficulties involved in bending a complete rim as one piece. Think about it. A Fox bender would be unusable.
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Re: perfect rib seam at tailblock

Postby Gordon Bellerose » Sat Jun 11, 2016 12:13 am

Barry Daniels wrote:That has been done, but there is no advantage to it and there are several difficulties involved in bending a complete rim as one piece. Think about it. A Fox bender would be unusable.

I realize those restrictions in most of our shops, but maybe in a factory they could use an inside mold and press from all sides. Just a thought....
I need your help. I can't possibly make all the mistakes myself!
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Re: perfect rib seam at tailblock

Postby Clay Schaeffer » Sat Jun 11, 2016 1:57 pm

The other downside to a one piece rim is the love of "book matching" we have come to expect. Think how miffed we become when we bend a side "wrong". It's only wrong because it doesn't book match the other side.
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Re: perfect rib seam at tailblock

Postby Bryan Bear » Sat Jun 11, 2016 4:54 pm

Yep and it is much easier to find a 30 inch defect free board than a 60 inch one. When I find myself wanting to make a small bodied instrument like an uke or mando or the like. I don't look for a 10 inch wide board to resaw for the back. A book arched back would both look better and be easier to obtain.
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