Double Bass How to keep ribs aligned when gluing top on bass?

[unbrokenchain]

Context then question:

I wanted to fix this,

but couldn't get much movement without feeling like I was going to break something. Rib was detached from the lining, lining was still in the right place on the back (with a bunch of cleats from where someone repaired it before). The top of the bass wasn't particularly well attached, so I just went for it and popped the top (this pic is before I did anything, not sure why my photos get flipped sometimes).

Got the corner blocks and linings mostly right, or at least a lot better, and put the top back on. Here's the same corner now.


Let it all cure over the weekend, set it up and it plays beautifully.
I did a relatively decent job I think, but the neck block glue joint wandered ~1mm north of where it was before (while first clamped) when I was gluing the tailblock. The result is that the neck angle is slightly steeper than before so I had to raise the bridge, and the ribs on the upper bout reveal about 1.5mm of unfinished top.


It was not perfectly aligned (and not well attached) before from previous repair, I think I actually improved the alignment overall so I feel good about the repair and am going to play it as is, but I'm sure seams will open up again so at some point I'll likely try and do it again a little more perfectly. But that's my question - how do pro luthiers keep the ribs exactly aligned before the top is placed? Do you build a jig for each bass, or is there some secret I'm missing?

 

[KUNGfuSHERIFF]

Internal braces to stop it from wandering around, and a little bit of muscle when fitting the top.

I do the blocks first, pull everything into alignment and then do the seams between the blocks.

 

[unbrokenchain]

I do the blocks first, pull everything into alignment and then do the seams between the blocks.

That's what I did essentially, neck block then tail block then each whole side w/ corner blocks clamped first. Seems like the right amount of neck support is critical for initial alignment. But internal braces? How do you get them out once the top is on?

 

[KUNGfuSHERIFF]

You dry fit them, cut to length, as soon as the top is off and remove them before you put it back on.

 

[eh_train]

When you're putting the top back on and the alignment is tricky in one area, try fitting a temporary brace that can be removed after the glue job: Fit a temporary brace, saw through 3/4 of the brace near the mid-point, attach a string near the saw mark and thread the string through the endpin hole. The top gets glued on with the brace inside, then you pull on the string and break the temporary brace so that it can be removed.

I hope my explanation is clear enough. It works!

 

[unbrokenchain]

... The top gets glued on with the brace inside, then you pull on the string and break the temporary brace so that it can be removed.

Brilliant!

 

[David Potts]

You might need a small hook to pull the rib out into its correct alignment before clamping. Make it out of a thin strip if metal, with just enough bent over at the end to do the job and yet easy to withdraw once the job is done. A pair of very thin wedges can assist with the gluing. So will a lot of clamps - I once made 60. And an artist's palette knife for applying the glue. etc, etc.

The first thing I do when the top comes off is to fix a length of wood between the top and bottom blocks. This is usually enough to keep the ribs in shape until I am ready to glue up. Otherwise the weight of the neck plus fingerboard will distort the shape badly. Before I start gluing I do a dry fit with enough clamps to foresee any problems, check that I have all my equipment ready and prepare myself mentally.

 

[unbrokenchain]

You might need a small hook to pull the rib out into its correct alignment before clamping. Make it out of a thin strip if metal, with just enough bent over at the end to do the job and yet easy to withdraw once the job is done.

Ah, another great idea I hadn't thought of!

The lower bouts worked out nicely, and the corner blocks are right, I think where I went a little off was not supporting the neck enough (I didn't want too much support because it pushed the neck/tail blocks toward each other), it drifted back ever so slightly. You can see the gap between the top and the neck repair area in this shot. It's tiny, but enough that the bridge had to be raised 3/8" or so. I put some shims under the bridge feet so the adjusters aren't out so far.

I guess the question now is which is more worth it - pull the top off again (or at least upper bout and neck block) to get that mm back, or make a new bridge to fit the new position. I'm more inclined to leave it alone until something else necessitates top removal, but fitting a bridge takes a while too.

 

[David Potts]

From the above picture all you need to do is color the visible white gaps with something dark like van dyke brown and get on with playing. Each time the bass is opened there will be some damage to the edges as splinters are torn out of the soft belly wood. Finally you are up for some re-lining (re-edging), hopefully not for many years. Do as much as you can from outside before the next really important occasion (IMO).

 

[unbrokenchain]

From the above picture all you need to do is color the visible white gaps with something dark like van dyke brown and get on with playing...

I'm with ya! The gap up under the fingerboard isn't even really visible (flash photo makes everything weird, but my house is really dark), the exposed unfinished part of the top (last photo first post) bugs me a little, if it were any wider I probably wouldn't leave it, but I'll just call it "within spec for a home repair" for now. The glue joint is tight all around, the bass is back setup and sounds amazing. I cut some thin shims of cherry for the bridge feet, not going to worry with a new bridge for now either. If I have to open the bass up again I'll get it perfect. I enjoy working on basses, but not nearly as much as I enjoy playing them.

 

[Don Hergert]

@unbrokenchain, as a quiet lurker in this thread, I'd just like to send a big congrats your direction for getting, and fixing this bass. From everything I'm reading, it sounds like a treasure. Happy playing now!

 

[unbrokenchain]

@unbrokenchain, as a quiet lurker in this thread, I'd just like to send a big congrats your direction for getting, and fixing this bass. From everything I'm reading, it sounds like a treasure. Happy playing now!

Thanks Don! It's a long saga and series of good trades (involving a van, an electric bass, and a Kay upright), that's resulted in this bass being in my hands. It's not that I'm totally broke, but music is my primary source of income and I own/live in a log cabin from the 1800s that needs a lot more help than any instrument, so that's where any extra money goes for me. I was hoping/planning to get a particular Shen SB150 but that instrument sold before I moved my other Kay. I saw a carved bass in need of help for really cheap, sprang on it that day. Thanks to TB I've learned how to work on my own bass like I do my house and car, so this poor musician has a pretty fine (if a little banged up) instrument! And with little enough invested in it that I don't mind messing with it a little and won't have to cry but so hard if it explodes in my "meagerly" climate-controlled house.

But yeah, I'm really happy with it. Carved and a Kay, think I've got exactly the tools I need at my level of career and ability.