Double Bass Reassembly Questions and Tips

[NC Violone]

Hello Fellows,

I'm about ready to reassemble this old Bohemian bass. Unfortunately the top and the back are both off. The form has been pretty well maintained.

What are the best practices for gluing up the top and back?

Which one first? I thought the top might first.

I also thought that clamping it up dry, getting it into proper postion, and then pinning it with small dowel might help.

My thought was that I would use straight edges to line of the neck, and also to make sure the angle of the neck is where it needs to be. The new finger board isn't on yet, but I can easily spot glue it temporarily. If I'm not mistaken, the measurement I'm after is around 150mm from the intersection of the top of the bridge along the plane of the fingerboard. Does this sound right?

This bass is like the other broken down Bohemian flat-back that come through here. $150.00 and a lot of sweat equity. So far it seems promising, but it certainly might sound lousy when it's done.

Thanks for any advice you can share.

 

[ctregan]

I think the back is usually glued on first. Clamp it with the inside of the back facing up so you can monitor the edge overhang dimension as you go. Also, consider using some kind of internal bracing to hold the blocks in proper position.
Do a dry run and choreograph your every move.

 

[NC Violone]

Thanks. I don't think it's desirable for the top and back to both be off, but the back was a wreck, and the top needed help as well, so I didn't see any choice. Also, the glue was so dry and brittle, but were barely hanging on anyway.

I guess what I'm slow on is how would you align the neck along the center seam of the bass, and the neck angle without the top on.

 

[ctregan]

A completely restored bass will perform better than one that was patched together. It sounds like you are doing the right thing.

You should be able to find the centerline of the bass with the centerlines of the upper and lower blocks. I would try to internally brace them into position.

To see if the neck is straight with the body, tack a piece of plywood flat over the ribs near the bottom block (like a top), transfer the center line to the plywood. Then use a long straight edge to line up the neck center line and the body canter line. You may need to use a square to raise the block center line up to the angled of the neck center line. Other people may have different methods.

I hope this is not confusing, It would be easier to explain with a picture.

 

[Matthew Tucker]

is the neck still glued in? What's the overstand?

look at your overhangs. Even all round? The last plate you glue on you may have to make some compromises. But all else being the same, I think I'd glue the back on first.

you should probably clamp it all together dry run first. That will give you some clues about neck adjustments you may need to make.

 

[arnoldschnitzer]

I would get the neck out of its mortise. (It should be relatively easy, as you can work the joint loose from both sides.) Then you will be better able to fit, align and glue the rib assembly to the plates. Afterward you will have a ridgid corpus which you can properly set the neck to. (Pitch angle, lateral alignment and overstand can be optimized.) I have learned the hard way that removing the rib assembly from both plates is not the best idea. I also think that gluing it to the top plate first makes sense because you are not dealing with tapers or bends, and because the top plate, being fragile softwood, needs to be stressed as little as possible. If you align the rib assembly to the back first, you will likely have serious overhang issues when fitting up the top.