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Double Bass Progress pic: 1/2 the ribs are glued up

D

Don Harris

Feb 21, 2003
273
6
Colorado Springs
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#1
Some of it went pretty smoothly, but some of it was a mad dash to get everything in place and clamped before the glue gelled, only to see gaps a little too late and have to take it apart, clean it up and try again. On the neck block I had it clamped and dried when I decided that there was a gap that was unacceptable. I got out the heat gun and carefully heated the wood on the side with the problem, reclamped, glue squeezed out, and now it's a perfect fit. Not everything came out as tight as I would have liked (perfection :hmm:), but it seems really solid. The other side "C" is ready to glue but I think I need to pace myself... On second thought, I think maybe I'll go heat up the glue. :) -don
 
#6
Doesn't that depend upon how accurately the rib fits the blocks?

I wanted all the pressure I could get, but I assumed my sins at the bending iron had found me out. A little too much here, not enough there, and pretty soon you need some real pressure. :-)

I don't leave quite that much overhang, so there is more room for clamps, but I am not satisfied with either my bending prowess or my clamping/gluing efficiency.

If the fit of rib to block is "perfect", does it require less pressure to successfully glue & clamp?
 
#7
arnoldschnitzer said:
I don't think that's enough pressure. Most builders use heavy counterforms covered in cork, then apply pressure with a pair of heavy clamps.
Click to expand...

I guess we'll find out. For the most part, there is virtually no gap between the ribs and the blocks. Also, you may be underestimating the lbs of pressure possible with bungee and cauls. The cauls were chalk fitted, so there's pretty even pressure on the joint. Plus, I worked really hard at getting the ribs bent to fit with practically no pressure. I tried putting high density foam between the caul and ribs, but didn't feel like it pulled it tight enough. When I was working this through in my head, I had a harder time imagining how to use regular clamps and have the flexibility as far as pulling from certain angles. The beauty of this is that if a caul isn't fully closing a gap, I can pull the bungee around another dowel (different angle) and usually pull it closed. I fully appreciate what most builders do, and your input Arnold, but if the goal is a solid joint, then I think (hope) I'm ok. I've also thought about not starving the glue joint by applying TOO much pressure. I suppose in this, as in all things, time and experience will show me if I've miscalculated.
 
#9
Right now the ribs are just under 9", but they'll be trimmed back to 8-3/8" at the saddle and 7-1/4" at the neck. I don't think that it will be oversized at all then. In fact, it's a pretty small bass. This is the first time I've bent wood, so I'm not sure how much the width adds to the difficulty. Thanks for the encouragement. -don
 
#10
Don Harris said:
Also, you may be underestimating the lbs of pressure possible with bungee and cauls. The cauls were chalk fitted, so there's pretty even pressure on the joint.
Click to expand...

I took another look at your photo, and I can see what you mean about the bungees exerting pressure. How long does it take you to get all that in place? My only concern is that with 3/4" material acting as your counterform, and it being clamped toward the ends, there may be a little springback. That might cause the center of the joint to have insufficient pressure. A trick of mine is to use heavier counterforms and make them slightly convex, thereby exerting force in the center when clamped at the ends.
 
#11
I've gotten pretty quick winding the bungees around, maybe under 20 seconds-then adjust things- and with a second set of bungees in another 15. I dunno. Time seems to distort while the glue is setting.

The counterform bowing is a concern to me too. I need to glue a backing board to them to make them stiffer. Thanks for the convex tip. A straight edge along the ribs at the block shows it to be straight and the corners are trimming up nicely though.
 
#12
I just glued an upper bout and put some of my 2" conduit pipe behind the caul as temporary remedy for being springy. Working fine. My baby food jar of glue in a little saucepan has tipped over in the water now a couple times. Gotta fix that.

I'm being really careful that I don't wind up a bungee and have it slip off a dowel and whack me in the face. This bass building thing is dangerous! Hot pipes, sharp blades, flying bungees...
 
#13
I took the mold with the ribs glued on to my luthier's group tonight. Our teacher checked out the joints at the blocks and thought that they looked great. That was a relief. He was, however, concerned about my using douglas fir for the end block. He too said that doug fir is very splitty and was concerned that the endpin would act like a wedge, and if the bass was set down hard, could easily split. So now I have to decide whether to inlay some cross pieces of wood into the tail block to discourage splitting, or unglue the lower bout from the tail block and make one out of basswood, which is what the rest of the blocks are made out of. At least I haven't done the butt joint yet, so I wouldn't be making too much of a mess of things. I was hoping to get the last rib piece glued on tomorrow (it's already bent) so I could get an outline for the top and start carving, but now I have to deal with the end block:eyebrow: .
 
#15
Don Harris said:
So now I have to decide whether to inlay some cross pieces of wood into the tail block to discourage splitting, or unglue the lower bout from the tail block and make one out of basswood, which is what the rest of the blocks are made out of.
Click to expand...

We all go backward to go forward at some point. If you remove the tailblock, don't try too hard to slip the rib/block joint. With the fresh strong glue in there, you are likely to damage the fragile rib. You would be better off taking the block out in pieces, eventually wetting and scraping the glue off the rib. If I were you I would do it, since repairing a split block is a huge job by comparison.
 
#17
If I ever had any worries about hide glue being strong enough to hold this thing together, I don't anymore. I started by using a little artist brush to add warm water at the edge of the joints and probing with a mechanic's rule to see if things would loosen up. It was painfully slow with barely any progress. Then I spritzed the ribs over where they meet the block and put the heat blanket on for a bit (this is where having the blanket on a dimmer with a temp scanner worked great. I kept it at 260F to 280F, so no scorching). I was nervous so I didn't leave it long, but I could tell that things were moving in the right direction as an edge was coming loose. So a little more water and a little more heat and things came off with no damage to the block (who cares?) or ribs. Where the heat blanket was sitting against the ribs above the block I think I caused a little more distortion/wavy thing going on across the grain from the heat. I'm no longer shooting for perfection, but rather, learning, so it doesn't bug me so much when I goof. That's what I keep telling myself anyway. Now I'm trying to clamp out some of the wavyness with a pipe and caul and a spritz of water across the grain. I think it might actually be helping.

I'm making the new block with basswood, but I have to cut the wood in half, change the orientation of the grain, joint it, and glue it back together for it to work. All of this with a circular saw, dozuki (sp??) and hand planes. It's all about the experience, right? This weekend there's a sale at Woodcraft, so I think I might buy the Rikon 14" Deluxe bandsaw and maybe a spindle sander (a jointer would be nice) so I can quit mooching off of friends, and quit getting so much exercise with hand saws and planes.
 
#19
Thanks for the link, clink (I'm on the brink of a blink I think...sorry, I use to be a songwriter). That one only has a 6" throat. If I get one I want to be able to resaw ribs and backs, so the Rikon, with a 13" capacity would work better for me. The Jet at Woodcraft has a more powerful motor, but I think only a 10" throat. I read on a guitar building forum that the Rikon 14 Deluxe worked well for resawing in that particular person's opinion, and guitar backs (1/2) would be about as wide as ribs.
 

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