Double Bass Advice on experimental (and crude) repair

[KUNGfuSHERIFF]

An overlaid soundpost would be appropriate and acoustically invisible if done well. It will be critical that you set the grain of the patch at least 45 degrees offset from the top grain.

 

[Saxophone Phil]

Is 45 degrees ideal? Would 90 be better? Sounds like this is the way to go.

dhergert - the goal is to take a bass that has been officially condemned by a luthier and turn it into a playable instrument. So sound quality is important, appearance is not - but laying in a patch like this has the advantage of not looking ugly.

 

[KUNGfuSHERIFF]

At 45 degrees the belly and patch will move roughly in sync. At 90 maybe not but I’ve done so successfully.

 

[Steven Ayres]

if I put cut a thin piece of spruce - say 1 or 2mm thick, cut to a circle perhaps 50mm in diameter - and put it right right above the soundpost (inside the belly), and shorten the soundpost by the same amount, would that be disastrous for the sound?

That's essentially what I was describing above, and it's a common repair.

 

[robobass]

45°? I thought the common practice was to rotate only a few degrees. More rotation gives more strength, in a sense, but what about shrinkage? Also, less rotation means less interference with the top vibrations.

 

[robobass]

Thinking about it more, the patch will have almost all of its stiffness along the grain. I really think you want to rotate it only as much as needed to prevent the cracks from pulling the grain of the patch apart. 5°? 10°?

 

[Saxophone Phil]

I think robobass has got it there - it seems to me that somewhere around 5° or 10° will be the best compromise between the strength of the repair and maintaining the natural movement of the wood. Anyone have a good reason to use a greater angle?

I've ordered a new bridge and strings (things take forever to arrive in New Zealand), and I'll begin as soon as they arrive. The first job though, is to dismantle a piano to get the spruce for the repair!

FWIW I've given her a name - she's "the Bride". As in the Bride of Frankenstein (she's being brought back to life, she'll have scars and bolts in her neck). Also references to Duchamp and Tarrantino.

 

[GretschWretch]

I think robobass has got it there - it seems to me that somewhere around 5° or 10° will be the best compromise between the strength of the repair and maintaining the natural movement of the wood. Anyone have a good reason to use a greater angle?

I've ordered a new bridge and strings (things take forever to arrive in New Zealand), and I'll begin as soon as they arrive. The first job though, is to dismantle a piano to get the spruce for the repair!

FWIW I've given her a name - she's "the Bride". As in the Bride of Frankenstein (she's being brought back to life, she'll have scars and bolts in her neck). Also references to Duchamp and Tarrantino.

Given where you live and what was filmed there, I say call her "Bride of the Dunedain." And inlay a big golden ring in the tailpiece.

 

[Saxophone Phil]

Ha ha! (but people down here in Dunedin would probably just think I spelled Dunedin wrong).

 

[Saxophone Phil]

Thanks for all the help I got here on this project - in the end she turned out beautifully - after around 50 or 60 hours of work. Here's the tale in detail...

 

[Sam Reese]

Hi Saxophone Phil,
I have an old Czech bass that has a bad crack in the top where the sound post resides. I am intrigued by the hole you cut into your bass. Has it held up well and/or developed any buzzes or rattling noises since you completed the repair? I told my luthier about the hole and he was concerned about structural integrity. Please advise, we will appreciate your input.
Sincerely, Studiodawg.
PS- anyone else with similar stories, please chime in and post some images or videos.

 

[Saxophone Phil]

My repair has held up well - you can see how long from the date of the first post. She's had a lot of use too. The bass came out really, really well. She's not loud, but not as quiet as some basses, has a beautiful midrange. No buzzes or other nasties from the repair. I've never had to open up the side door, but it's good to know I could if i needed to adjust the soundpost if needed.

certainly my approach was very, very easy and cheap, and the bass plays great. Mind you - she was never an expensive bass, so I would think twice about this method if your bass was good enough to justify doing the repair the proper way (remove top, gouge out hole for patch) which would of course be very expensive.

 

[craigie]

Great job mate! Nice to see the video too!

 

[robobass]

Congrats! You rescued a ten foot pole bass (how my local luthier thinks) and turned it into what appears to be a very playable instrument. I am also a hobby repairer. The only thing I would have done differently would be to remove the fingerboard, clean the surfaces, and re-glue with an ebony shim. The reason being that if the joint isn't hide glue, then you might get further warping, and a shim would add stiffness and increase overstand. There is also the CF rod technique to consider. Otherwise, I personally could not invest so many hours in such a project. It would make more economic sense for me to just work at my job and pay a luthier. Still, I do want to someday open up my Pfretzchner and press out all of the top sinkage with plaster molds. This job will probably take hundreds of hours, and not be economically rational in the end. But, I just love the bass, which has done me very well over the thirty years I've owned it.

 

[dan1952]

I have a 60's era (70's?) Hofner-built Anton Shroetter plywood bass that had a badly bowed neck, but with a nice thick ebony fingerboard. Contrary to what most folks here recommend, I planed the fingerboard straight, shaping it to the original radius as I went. I used decreasing grit sandpaper and emery cloth to polish it up. The action (no gauges available) is now as low as any jazzer could want, and it has stayed straight for nearly 3 years. Wear a mask, ebony dust is evil!

 

[dan1952]

OK, here's the situation. I'm a sax player who's just fallen in love with double bass. The only problem is I can't afford to buy a decent one. What I do have is a 1950s German student-level bass that has serious problems. Despite these problems, I find I'm picking the instrument up quite quickly - I play a little bass guitar, so a lot of musical skills transfer, and I'm doing OK. And I'm loving playing it. But the bass... well...

The first problem is that there are two cracks behind the bridge, above the soundpost. (I've attached a photo).

The second is that the neck is bowed, and/or perhaps on the wrong angle. This means that the bridge (which is deformed) is as low as it can be taken, yet the strings are too high in the middle of the fingerboard.
She does look pretty, in a distressed kind of way though.

The local luthier points out that it was never a great instrument: fingerboard made of non-ebony mystery wood, plywood back and sides (but carved spruce top). To repair it properly will cost far more than it is worth.

Now here's what I'm planning to do. I'm asking your advice if there are better ways to approach these problems or if what I'm intending to do is completely doomed. But please remember - I can't afford to do the obvious thing and buy a new Chinese student bass (i.e. my wife won't let me). I do have time, tools, and some skills at repairing guitars and saxophones.

The cracks: Yes, I know the approved method is to take the belly off, make a plaster cast to support it, and carve out and replace the wood from the inside. That's beyond me. So what I'm planning on doing is making the repair from the outside. She's not a pristine instrument, so a visible patch on her belly might just look funky in a frankensteinian way. I have an old piano soundboard (100 year old spruce!) that I can use for the wood. I'll shave half the thickness of the wood away, in a rectangular shape over both cracks, and glue a new insert in, then use a scraper to take the new piece down until it's flush. I could also put studs on the inside. Another idea might be to use harder wood (maple?), but I'm guessing that this area of the belly is pretty critical in terms of sound production.

The neck - my intention is to use a scraper and sandpaper to try and even out the relief on the fingerboard - effectively shaping the fingerboard to compensate for the bowed neck. If I take 2 or 3 mm off at the nut, then I think I'll be able to get a bridge to sit right. The bridge needs to be replaced anyway.

I'm a blues and jazz player, so a wierd-looking bass is not a problem for me, and she will mainly be heard through a pickup anyway, so the acoustic sound is not as critical as if I was an orchestral player. And have you ever noticed Willie Nelson's guitar?

I outlined above how I planed the fingerboard straight. Contrary to what some folks have said, the neck won't warp more than it already has, so this "repair" should work. Although most bass players would like to think that there is some magic involved in bass repair, the same principles apply in guitar lutherie when it comes to this. The tension of 4 bass strings isn't that much different than 6 guitar strings, and a piece of 60 or 70 year old maple is done warping. It probably did that when it was nearly new and somewhat green. As for the top cracks, some clamps to flatten the cracks, some hide glue, and some small cleats across the ends of the cracks should stabilize them. Cheap and relatively easy fixes!

 

[dan1952]

Oopsie, didn't see that it was completed.