Advice on experimental (and crude) repair

Discussion in 'Setup & Repair [DB]' started by Saxophone Phil, Jul 4, 2018.

  1. Saxophone Phil

    Saxophone Phil

    Jul 4, 2018
    Dunedin, New Zealand
    owner of 1959 Guitar Co.
    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?

    Attached Files:

  2. Hi,
    I wouldn't care much about the cracks next to the bridge, until they do something weird when you play (like buzz, or are dropping into the body or so). On my bass, luthier repaired cracks using patches of wood cca 3x2 cm glued to the cracks from the inside. He mostly (maybe exclusively) used the traditional glue made from cooked animal bones - don't know english for that, painters use the same for preparing the canvas. This might be doable without the need to open the body - luthiers use curved pliers to do that (and dentist mirror to see what they do). I don't know exactly, but I was surprised what major repairs they can do even with closed body. I wouldn't patch it from outside, it will look ugly.

    About the neck, I'd go to a luthier for advice. Luthier told me that the 'point' where the neck is connected to the body often gets loose, which is solved by putting the 'bone glue' into the holes, maybe with some wood patches or wooddust putty too, the goal being so that you feel the neck holds really sturdy. Also, old basses had more curved fingerboards because they were made for gut strings with larger vibration amplitudes. My bass (cca 1920?) had it too, the fingerboard was walnut. Luthier told me the best thing would be to replace the fingerboard, so he did. So I guess you can try to brush it and if you do it wrong, you still can go to a luthier. Check Rufus Reid Evolving Upward book, there are some texts about what the height of strings should be.

    Sometimes I'm surprised that the bad plywood sudent basses actually, when amplified in a normal gig situation, sound 'less compromised' than the solid wood good ones, which need to deal with too much bass freqs, too much vibration resulting in feedback troubles and so. Of course better bass sounds better in the end, but don't worry too much - if it plays like you want it to, then it's a great bass.
  3. Saxophone Phil

    Saxophone Phil

    Jul 4, 2018
    Dunedin, New Zealand
    owner of 1959 Guitar Co.
    Thanks, JJ. I think I can manage gluing 3x2cm studs over the cracks on the inside with hide glue - but conventional wisdom holds that the location of the cracks - over the sound post - means that the studs won't hold, and the location means that vibration is not being transmitted from the bridge to the belly properly, therefore messing with the sound.
  4. I have the same studs covering the same cracks as yours and they stick for about 5 years now. Luthier did it though, maybe there's more to it than I know. I vaguely remember a talk about the glue - that it needs to be permanently flexible to hold for years, and that modern glues like epoxy are unfit, because they are too hard and therefore will break. He also spent a lot of time using different kinds of putty, including one made from fern pollen.

    I think that more important for transferring the vibrations is the position of the soundpost inside the body. Players experiment on this, moving the soundpost using a string somehow. I never tried. I bet you can find the details on the web.

    I may be wrong, but generally I think that one or two cracks here and there will not affect the overall sound of the big all-vibrating body very significantly, bigger problem could be a buzz occuring on some tones. The cracks below the bridge are probably normal, as there's the biggest pressure possible in this place. Patches solve it good enough. I think that the span between the patches is like 5-6 cm on my bass.

    Friend once told me that he plans to build a double bass from scratch according some plan on the web... look for informations, surely there will be plenty. I like improvisation, but I wouldn't improvise here when the information can be had. Though, from what the luthier told me, I got the feeling that almost everything can be fixed like the bass was made from modeling clay... for a cost.
  5. robobass


    Aug 1, 2005
    Cologne, Germany
    Private Inventor - Bass Capos
    The cracks don't look too bad at the moment. Worry about the neck. A bowed neck on a cheap bass is often the result of the wrong glue used to bond the fingerboard to the neck. If you can get the fingerboard off without destroying it (pickling vinegar in a syringe bottle and loads of patience), then you might be able to clean up the surfaces and glue it back on with hot hide glue (that's what we call it). You can physically straighten the neck a bit while gluing to remove some of the bow. In the end, though, playing a bass with a badly shaped fingerboard is like driving a car with a flat tire. It can be done, but it ain't worth doing.
  6. You’re not Willie. Willie has a repair budget.

    One of two things is going to happen. Either the soundpost is going to come through the top, or you’re going to develop tendinitis from that bowed neck and those lousy strings.

    Trade it in on something that won’t hurt you.
  7. robobass


    Aug 1, 2005
    Cologne, Germany
    Private Inventor - Bass Capos
    What's up with Willie's guitar though? It hurts me to even think about!
    Last edited: Jul 4, 2018
  9. notabene


    Sep 20, 2010
    SF Bay area
    Read up for a while. Repairing the top cracks is probably possible without taking off the top. But read up on patch material, shape, et al. And learn about hide glue (not in a bottle). For the neck, photos would help, but, again reading up would help. I too am a sax player who has repaired three totally wrecked basses and made some nice basses out of them. You can learn to correctly fix this, but life is short, and developing the "feel" for really getting the most out of an instrument in which every change influences everything else takes a lifetime. One can but try.

  10. Steve Swan

    Steve Swan

    Oct 12, 2004
    Burlingame, California
    Retailer: Shen, Sun, older European
    The wise-ass answer is to trade your wife in on one who will allow the fairly minor expense of a good chinese student bass for $2,000, more or less. Compared to other mid-life side trips such as buying a Porsche, a motorboat, or having a kept mistress in an expensive apartment, it is a pretty small expense. Life is too short to play on crappy get-by instruments. Get something that is a good value in an entry level instrument. You will enjoy the experience 10 fold more.
    Fretless55, lurk and jsf729 like this.
  11. Steven Ayres

    Steven Ayres Supporting Member

    Mar 11, 2007
    Northern Arizona
    If you're going to patch the top, make a thin spruce patch a little longer than the crack and a couple of inches wide at least so it will catch the sound post. Make the sound post the right length so it doesn't stress the top, and you'll be fine, the hitch will be acquiring the necessary long-throat, low-profile clamps. (If you can't clamp it up right, don't bother, it'll just be an ineffective mess.) The neck could be a bigger hassle; use a straightedge to measure the actual relief at its greatest and its position on the fingerboard, and let us know. The tip about the wrong glue is a good one.

    Tinkering with a neglected bass can be rewarding, I get that, just so you're aware that it can eat up a lot of time and still come out wrong.
    TwentyHz and Tom Lane like this.
  12. Saxophone Phil

    Saxophone Phil

    Jul 4, 2018
    Dunedin, New Zealand
    owner of 1959 Guitar Co.
    Thanks for the insightful comments - yep I realise this will take time and might still fail.
    Neck bow measurements -
    E string - 3mm at the point where you finger Bb
    G string - 3.5mm at the point where you finger Eb (the curve is different on this side - the fingerboard is lower for a longer stretch than on the E string side - but note that there's a bevel under the E string). The E string is OK to play, and has a reasonable relief: the bow is more manifest in the other strings.
    measured by holding the strings flat at the nut and bridge ends of the fingerboard, and measuring the gap.
  13. craigie

    craigie Guest

    Nov 11, 2015
    I have a cheap Chinese bass with a similar neck problem and it’s not worth the expense of having a luthier install a new fingerboard. It’s not even worth the expense of buying a fingerboard online and installing it myself. So I’ve been waiting to figure out how to get a suitable piece of wood and shape it.

    The issue was the cheaply made neck which bowed forward. This caused the fingerboard (painted softwood) to curve our right at the point where it meets the neck. I cut it off (vinegar and anything else didn’t work- it was glued solid with very hard glue). Then I laid the bass down with weights on the headstock to straighten the neck back.

    If you won’t play into thumb position I say just cut the fingerboard off where it meets the neck. Maybe leave a strip along the E string which isn’t bad as you say, to support your right hand. Then you can try and shape what’s left to get a reasonable relief.

    If it’s doing what mine did because if a bent neck, trying to carve or plane down the fingerboard will just make it curve forward more since it’s thinner and has less bending resistance and where it meets the neck is a point of inflection.
  14. Saxophone Phil

    Saxophone Phil

    Jul 4, 2018
    Dunedin, New Zealand
    owner of 1959 Guitar Co.
    I can think of ways to support the fingerboard - if it gets too thin after I sand it flat I can glue a piece of kowhai (NZ wood similar to maple) underneath to keep it straight.

    I don't think weights will help your neck - even if you straightened it out once before, if it bowed under pressure before it will do so again. You could get a cheap ebony fingerboard from AliExpress though. The local luthier here said he thought that if my bass had an ebony fingerboard (instead of mystery hardwood) the neck might still be straight.

    It is worth thinking about how high I might play in thumb position though - if the extreme end of the fingerboard was not there I could get a better action in the main playing area. Seems a pretty ruthless idea, but perhaps ruthlessness is what my poor bass needs.
  15. Saxophone Phil

    Saxophone Phil

    Jul 4, 2018
    Dunedin, New Zealand
    owner of 1959 Guitar Co.
    OK, I have a plan.
    1 - I'm going to make an access door in the C bout - there are a few pictures of similar projects on TalkBass, and it looks doable.
    2 - This will allow me to get easier access to the inside. I'll still use a spruce patch on the outside of the belly, but now it will be much easier to put a row of cleats in the cracks from the inside. Also easier to clamp, and fit the soundpost. I won't need to buy a fancy soundpost tool!
    3 - to fix the neck the main job is to reset the angle. So rather than trying to fix it with scrapers and sandpaper I'll remove it and re-fit it as a bolt-on neck, which will be possible since I will have access to the inside. Again, there are some good pics on here. The bolt on approach will allow me to shim the joint until I get the angle perfect. And while the neck is off it will be easier to sand it straight.

    One suggestion I've had for removing the neck is a hypodermic syringe filled with hot water.
    Anyone have any thoughts on where I might go wrong?
  16. dhergert

    dhergert Gold Supporting Member

    Jan 17, 2018
    Blue Zone, California
    Not necessarily wrong, but interesting...

    My Alcoa aluminum bass has a 7"x7" trapdoor for access in the driver side C, installed during the time when it was being repaired and hot-rodded (before I owned the bass). This trapdoor is hinged and uses velcro to keep it closed, and to keep it open. I've found it handy for a myriad of adjustments and a few key mods since I've owned the bass, and I've even been known to leave the door open for my cats to catch dust bunnies. A big plus is that it's very nice to open it up as a driver-side sound hole to increase volume where I can benefit from it.

    My suggestion, if your bass would still be structurally sound enough to do so, is to keep this access door you're considering as something you can open later on, maybe even making it easily open-able for use as an auxiliary sound hole for your playing benefit.

    Also, recently a modern aluminum bass has been seen here in TB that has both a driver-side lower bout access hole, and an upper-back plate access hole for neck related adjustments, both which are normally closed but can be simply re-opened as needed. Your bass's neck surgery may also benefit through time from a similar upper-back plate access hole, again if your bass would be structurally sound enough to do so.

    I'm not a bass luthier and we do have excellent luthier advice available here from a number of very good folks, so consider my thoughts here as only from a user standpoint. Adding one or both of these access doors to your bass may be less practical than I could predict.

    Best of luck with this interesting project!
    Last edited: Jul 5, 2018
  17. turf3


    Sep 26, 2011
    Probably not germane to the question at hand, but I have heard of drilling a few tiny holes in the piece to be patched, then using nylon monofilament line pulled tight from the outside to clamp on the inside. The tiny holes can be filled in with some brown wax later.

    Also have heard of using neodymium magnets as clamps (if you have ever had any experience with these, they are VERY STRONG).
  18. Drilling holes to effect a crack repair is Paleolithic malpractice.

    OP, if you reinforce a soundpost crack with cleats, how do you expect to refit the soundpost with cleats in your way?
  19. Saxophone Phil

    Saxophone Phil

    Jul 4, 2018
    Dunedin, New Zealand
    owner of 1959 Guitar Co.
    Well, you can't put a cleat right under the soundpost - the nearest cleat would have to be a cm away. I'm only thinking of cleats because they would be easy with an access port.

    QUESTION - 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? With an access port it would be a very easy repair, and easy to clamp (just put soundpost back and bring strings up to pitch). I realise that what I would be doing is to thicken the belly at a crucial point, but given the size of the instrument (compared to a violin) would that be enough to compromise the sound to a perceptible degree?

    And if the effect was to make the instrument a little quieter - she might play just as well when amplified (and might even be more feedback resistant). Another plus side to an access door - I could do the simple repair described above, and if it had a bad effect on the sound it would be easy to undo (I'd need to buy a new soundpost, but the patch could be removed easily).
  20. dhergert

    dhergert Gold Supporting Member

    Jan 17, 2018
    Blue Zone, California
    Sort of shy about it, but this is a similar concept...

    Here's what I did to spread the soundpost tension over a wider area of my Alcoa bass in order to protect some weld repairs that had been made to it.

    It is much easier to match 6 points to the curvature of the top table than it is to match a solid surface to the curvature of the top table (especially when there are repairs to avoid).

    It works nicely, and in fact from a tone and volume standpoint this has actually been better for my Alcoa than the standard soundpost (which I've kept unmodified). However keep in mind that an Alcoa bass is a much different beast than a wooden bass.

    Isn't the OP's project a true jungle repair? It seems to me the whole aim of the OP's work here is to preserve the top and make the bass playable, at this point probably with little regard to how good the tone and volume are. Short of this work, it sounds like the bass's future is in grave doubt. Have I misunderstood this?
    jleguy likes this.