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Need advice re neck reset with neck angle change

Discussion in 'Setup & Repair [DB]' started by Stu Elston, Jul 6, 2017.


  1. Stu Elston

    Stu Elston

    Apr 25, 2004
    Knoxville, TN
    I just posted, in the general Basses [DB] area, an overview of the DB in question here; the post is titled "German/Czech (?) Ply Flatback ID, ca. 19??" This old girl is pretty quiet, because her bridge is pretty short - 5 1/8" measured at the top of the arch between the D and A strings. Chuck Traeger's book suggests it should be more like 6 3/4". The top seems pretty sturdy, so the increase in static pressure from the downward component of string tension will hopefully not be an issue, and the increased dynamic component (from vibrating strings) that will accompany an increase in bridge height should increase the volume.
    You can see the shallow neck angle that is responsible in the image attached to this thumbnail: CB-bass-side-full.

    Now, the neck joint seems to have failed, so it seems like a good time to address the wrong neck angle. Here are a few shots of the neck join failure, beginning with one from the player's perspective: CB-button-neck-joint-failure-0. CB-button-neck-joint-failure-1. CB-button-neck-joint-failure-2.

    It looks to me as if the only thing keeping the neck stable at this point is the button. The string tension acts to rotate the neck around a horizontal axis through the top of the face of the neck tenon where it bears against the upper edge of the face of the mortise, and as it does so, the bottom of the heel rotates into tighter compression against the button (actually, the shim between the button and the bottom of the heel). Interestingly, at this moment, the bass is in a stable state of tune, and a week ago I returned from a week-long bluegrass camp where I played and jammed for at least 3-4 hours every day, without noticing anything wrong with my tuning. I have noticed the gap between the heel and button in the past, and it did seem a bit larger at the camp, but I was too busy learning tunes and playing bass to think through what it meant.

    BTW, I read a recent thread here about the important and underappreciated role that the button plays. If I have analyzed my case correctly, I have another data point in that discussion.

    A little history is in order. I've had this bass since Fall, 2006, and it was rehabbed sometime around roughly 2004 after having been rescued at an estate sale. I don't know much about the details of the rehab, but there is evidence (pictures later) that the back was at least partially removed and that work was done on the neck. A crack in the bass-side upper bout rib was repaired. The fittings (endpin, tailpiece, bridge, a pickup) were replaced/upgraded at that time. The neck joint failed in January, 2013, 4.5 years ago. I took it for repair to the local guy (gonna leave names out of this) who was rumored to have been involved in the rehab. He claimed not to remember having worked on the instrument and I clearly remember him saying that the bridge did not look like his work. He did not say a word about the low bridge height, nor offer to fix the neck angle at the time. I've only gotten serious about this bass in the past 3 - 4 years and was naive at the time and didn't know to question the height of the bridge. The luthier (who, BTW, is fairly highly regarded by local performing guitarists and fiddlers) did reset the neck and the bass sounded better afterward - I believe he adjusted the sound post a bit.

    So - the first neck joint lasted about 8 years and the second one lasted 4.5 years. Is this nomal, abnormal, or somewhere in between?

    Now on to the repair . . . I want to achieve, in addition to a stable neck joint, a higher bridge. I'll shoot for around 6.5" (from 5.125"), which is a roughly 25% increase (actually closer to 27%). The geometry associated with rotating the neck from its present orientation to a higher angle is pretty simple, and is described in Traeger. Basically, with a distance of 22.2" between the front face of the neck butt (under the fingerboard) and a line between the inside notches of the f holes, and a distance along the face of the neck butt between the top of the bass and the button of almost exactly 6", a shim that tapers from zero at the button to (6/22.2) X (the increase in bridge height needed) should provide the needed correction. I think I can get about 0.2" by increasing the overstand (currently measures 0.81", Traeger recommends 1 +/- 1/4"). I like an overall height increase of 6.5-5.125 = 1.375", which is reduced to 1.175" by the overstand increase. Plugging this into the formula above, I get a required shim thickness (at the top surface of the bass) equal to (very nearly) 0.32". The mortise appears to be about 3/4" deep, so this might be workable.

    I guess it is time to think about the condition of the neck block, because I have been toying with the idea of a bolt-on solution. So I have a sound-post-trap-door, through which I took the following photo: CB-neck-block-interior.
    Whoa! But first, notice the cleats repairing a crack in the bass-side upper bout rib - clear evidence that the ribs are solid in spite of the ply top and back (I think I mentioned this in the post over in the Basses [DB] area.

    The two large pieces glued to the neck block look to me like spruce, 1/8” thick; note the dent made by a clamp(?) in the lower one. I don’t know whether these were added during the most recent neck reset or during the original rehab. They look newer than the rib crack cleats – and the repaired rib crack has been part of this bass as long as I’ve owned it – but that could just be due to the cleat wood coming from a different piece of stock than the neck block pieces.

    Does the presence of these pieces tell me that someone split the neck block in the process of removing the neck at some point? If so, does that make a bolt-on neck solution impractical?? I’m thinking that the bolt(s) could have heads inside the body (under fender washers?) and tie to threaded inserts in the neck heel. You could bore holes from the outside/rear of the neck heel clear through the neck block, with the neck correctly positioned, of course. No way am I going to drill from the inside unless I remove the back, and if I remove the back, I might as well replace or at least investigate a repair of the neck block. I think I have the nerve to attempt to reset the neck, and even change bridge height through a combination of increasing the overstand and increasing the neck angle with a tapered shim between the face of the tenon and the neck block mortise, but I ‘m not sure I want to R&R the back.

    Ideas, anyone?
     
  2. Ortsom

    Ortsom Banned

    Mar 23, 2016
    Stu,

    interesting instrument: ply top & back + solid ribs, low bridge. But I don't know age or where it came from, nor do I have answers to many other questions you ask. It does not look exceptionally old to me, and it might well be 1st part 20th century, as you say, or maybe even newer. It might not be a shop/factory instrument, but instead something assembled from a factory-made rib cage & other parts. But all that is pure conjecture.

    Nice access port, and I see your (5¼"?) HD magnet found steel in the neck joint. Some other comments:
    • IMO a proper neck joint should last at least till one drops the bass. Absent of that, last several lifetimes.
    • Yes, the button is important; some adjustable or removable constructions only hang on the button. Via the button the heel pulls at the back to build-up the torque to keep the neck in place. As the button is farthest away from the pivot point at the top, if the force acts there it is lowest. Yet IMO this button graft seems a little bit pointless & largely cosmetic, as it does not overlap in a long enough seam with the back, hence is not likely to be very strong. Nevertheless, it still appears to be in place, and the glue failed a little more inward, between that shim & heel.
    • Your heel might be hanging on some bolts only.
    • The 2 pieces of x-grain spruce might be covering something up, but I cannot see a split in the block.
    • Before you plan to take of top or back, or replace the block, have a good look at that glue that was used to attach top & back to the ribs. It might not be hide glue.
    I'd first get rid of those blackened pieces of spruce (?) at the sides of the heel, maybe you'll see more, possibly 2 bolts/screws. But more likely the heel tenon will stick into the mortise in the neck block, and then you still don't see anything. Does wiggling front <--> back tell you anything? Of course the strings are gone.

    Then, maybe you can remove those 2 pieces of spruce on the block, through your access port, though that might be more difficult than it seems. You might find the heads of screws below it. If so, take them out & the neck comes off. Or give'm bigger rings & tighten to attach more firmly (though their location might be too close to the top, the forces would be lower if the bolts are close to the back). Maybe those screw heads have been pulled into the (soft) block, due to the string force; that would look like this.

    On the bridge height, break-over angle, neck angle: in my opinion it is not the neck angle or the break-over angle that co-determine how loud the instrument is, but of those three (choosing my words carefully here to avoid the ozquisition) only the bridge height. The magnitude of the activation (or actuation) of top & back, as a result of a lateral string motion, is proportional to the bridge height, and independent of the other 2. In fact, as the break-over angle increases, the static downward load on the system increases, which tends to stiffen-up the system & make it less responsive. And of course, given overstand, string height & bridge location, the neck angle is fully determined by the bridge height, via simple trigonometry.

    If there are a couple of screws/bolts in there, and you manage to get them out cleanly and the block looks fine, I would just plug all holes properly with wood. Then I suggest to make a hinging adjustable neck, as shown elsewhere on TB. Make an elevated hinge point near the top, and tightening a bolt near the button will increase bridge height, & v/v. Or otherwise provisionally test the bridge height you want, with tapered shims or so. Using the existing screws & holes may not work for adjusting the neck angle: bending the bolts during tightening will cause them to shear, so that you instrument may explode.

    I recommend to also test for the desired breakover angle, by changing the saddle height. Higher saddle --> lower load --> louder is what I found on another instrument.

    Thanks for the riddle & Good luck!
     
  3. Matthew Tucker

    Matthew Tucker Commercial User

    Aug 21, 2002
    Sydney, Australia
    Owner: Bresque Basses, Sydney Basses and Cellos
    No matter how stable it feels, the fact that the neck joint is not solid will be robbing the bass of tone and volume, and the change in neck angle obviously won't help the bridge height. Unlike on a violin, the button is actually not really that important on a double bass with a reasonably deep mortise. What IS important is that you have good solid well-fitted contact between the neck and the block, whether through the use of glue or a bolt or whatever. If anything has any "give" in it, you're going to lose sustain, volume and tone.

    To achieve a solid neck joint and a higher bridge, you will need to remove the neck; if the block is split - and you will see this when you remove the neck - you will need to replace it with a decent one (an even bigger job involving removing the back); rebuild the mortise with very slightly thicker sides, and shape the root of the neck smooth and flat, extended as far as you need at the heel. Then re-set the neck properly centered and at the correct angle for the bridge height you want. A shim is usually not necessary; you simply remove wood from the back and sides of the floor of the mortise as you fit the neck to get the overstand and bridge height you want.

    It is a difficult job to do well even if you are an experienced luthier. Much harder than adding an access port. Repairing the button securely is even harder. If you are determined to do it yourself, I'm sure you can do it. I suggest you choose the advice you take very carefully, and keep things simple.

    Once everything fits exactly, I think whether you glue or bolt will make little difference to the sound.
     
  4. robobass

    robobass

    Aug 1, 2005
    Cologne, Germany
    Private Inventor - Bass Capos
    :):):)
     
  5. Stu Elston

    Stu Elston

    Apr 25, 2004
    Knoxville, TN
    Thank you, Matthew and Ortsom, for many good suggestions. I have a lot to check out and think through before I come up with a plan or solution. I had ordered a Thompson bass from The String Emporium last week, based on having seen, heard, and played one owned by a fellow student at a bluegrass camp earlier this summer, and picked it up at the Nashville air freight terminal yesterday, so now I have something to play while I take the time to do this one right.

    Ortsom said, "I see your (5¼"?) HD magnet found steel in the neck joint." Good guess, the magnet is indeed scavenged from a 5 1/4" hard drive head motor. But it is incidental, sort of. It's (it was) held on the bass-side upper bout rib with double sided foam tape, and serves to attach a steel binder clip that in turn holds a flip-book of chord charts. But your remark got me to realize that a nice strong (like neodymium) magnet is one way to possibly detect the presence of screws involved in a neck joint. Alas, after removing the magnet and tape (and goo), and scanning the neck area with the magnet, I can feel no attraction that would indicate a ferrous metal object. I'm not sure how deeply a steel screw could be embedded in wood and still be detectable this way, so I'll have to experiment on that, a little, tonight.

    I also need to confirm that I'm dealing with hide glue in the old work done in the neck area.

    I removed strings/bridge/pickup/tailpiece last night. The neck joint is clearly broken - it moves when firmly wiggled. It seems more free to move laterally (wiggle motion from bass to treble side and v.v.) than in the perpendicular plane, from the backside towards the top and v.v., for what that's worth. It does move in both planes, just more laterally. But it is not so loose as to suggest that it will be trivial to remove. So time permitting, tonight I'll break out a thin palette knife and some hot water and start by removing those black trim strips, then go from there, slowly, carefully . . .
     
  6. RSBBass

    RSBBass

    Jun 11, 2011
    NYC
    Be aware that not all screws are magnetic.
     
    Matthew Tucker likes this.
  7. james condino

    james condino Spruce dork Supporting Member

    Sep 30, 2007
    asheville, nc
    Did I read this correct: you took your BASS to a fiddle / guitar guy, NOT a bass guy- twice- and are wondering why it is not holding together like a BASS?????? Is the banjo guy next?

    Knoxville is an hour and half drive from Asheville.....

    j.
    www.kaybassrepair.com
    facebook @ Kay Bass Repair
     
    salcott and Matthew Tucker like this.
  8. Matthew Tucker

    Matthew Tucker Commercial User

    Aug 21, 2002
    Sydney, Australia
    Owner: Bresque Basses, Sydney Basses and Cellos
    James I read it that Stu WANTS the fun of a button re-repair ... :)
     
    james condino likes this.
  9. Ortsom

    Ortsom Banned

    Mar 23, 2016
    Stu, congratulations with your new bass!

    If the neck wiggles while the heel really does not want to slide forward, it's probably hanging on some screws, with play having developed as outlined above. As you cannot see any from the outside, they are likely below the mysterious patches on the block, on the inside. If you manage to get them out through your access port, you'll have very little damage & are ready to go for the next stage. If you can't get them out that way, it'll be a bastard.

    We all know not all screws are magnetic, we have been over this before extensively. And even if there are screws, and even if those are magnetic, I'd be surprised if you could feel them that way, and that the magnet would stick in the position of the photo, because of the distance. And Stu not previously saying anything about the magnet sticking there is another give-away. HD magnets are quite strong, but have a strongly curved field that is spatially limited. With a magnet like that, you can feel maybe 10mm deep at best (?). But the magnet was there (thanks to double-sided sticky tape), so I had to mention it.

    Try the magnet on the inside, over the spruce patches. If you feel anything there, then you know. But if you don't feel anything there either, that doesn't mean there are no screws there: they could be sunk beyond the sensing depth, or non-magnetic. Cheap to try.

    The choice to contract-out such a repair / upgrade to an instrument like this is up to the owner.
     
  10. Stu Elston

    Stu Elston

    Apr 25, 2004
    Knoxville, TN
    Gee, it's hard to know where to start, there are so many interesting comments and suggestions to work with . . .

    First and foremost, I have very little in the way of concrete information about the intrinsic value of this bass - as in, is it likely to be worth the $, or my time and effort, to fix it? There's obviously a second factor involved, which is how extensive is the damage, and what will it take to repair that. I don't have a good feeling, at this point, for either side of that comparison - value vs. cost-to-repair, with cost either involving outright money, or time and effort, or possibly some combination.

    I put a post in the general DB basses section to get some feedback on the value side of the comparison, and this thread in this section of the forum to get the other side.

    James, I know that you're roughly 1.5 hours away, and will explore this with a PM. BTW, the bass may have been to the "fiddle / guitar guy" twice (if he actually did do the original rehab) but I only took it to him once and I think it is clear I'm not taking it back to him. I went there because the musician who oversaw the original rehab recommended him, but I don't actually know that he did the original work. I do know that he has (or at least had at the time I took it to him for the neck reset) a contract to work on all the stringed instruments for a local high school orchestra. So it seemed reasonable at the time to take it to him . . .

    Within limits, Matthew is correct, I would really like to be able to do the needed work myself, and really would consider it fun - LOTS of fun (couldn't find a jumping-up-and-down emoticon, consider it inserted). Background: I'm a PhD experimental physicist; I have worked with both magnetic and electrostatic charged-particle spectrometers and ultra-high vacuum systems. I've designed and constructed these devices and their components by hand, sometimes from raw metal stock, with both hand and machine tools. I do know a bit about magnets and non-ferrous materials, including non-magnetic (e.g. type 304) stainless steel hardware. This experience can make me seem a bit arrogant about DIY stuff, but I've also been around long enough (nearing retirement) to have made lots of dumb mistakes and to have learned how to recognize when I'm getting in over my head . . . and I realize that none of this, by itself, translates into experience with wooden objects (although I do have a little of that).

    I have removed the black heel trim strips that Ortsom referred to to further explore the neck join, and I think I can see that it is going to be real trouble getting the neck out without extensive effort. Two factors contribute to this conclusion: (1) When I wiggle the neck, the wiggle doesn't reveal a crack in the glue joint immediately adjacent to the neck - it reveals several (roughly) parallel cracks in the adjacent wood of the mortise. Those cracks run in the wood at an angle to the nearby neck glue joint. This adjacent wood is either part of the neck block or a shim inserted between the neck and the neck block - I can't tell which. And I was unable to take a picture that shows this. (2) I cut away, with a sharp knife, a blob of glue that had squeezed into a gap between one of the trim strips and the neck. I was unable to melt this with a heat bath like you'd use to melt hide glue flakes. I'm afraid that if I push my luck with brute force, I run the risk of doing sufficient damage to require removing the top and replacing the neck block. But I'm not sure I'm reading these "clues" correctly. And, of course, it may be that a neck block replacement is unavoidable in any event.
     
  11. So the neck was set with carpenter's glue? Awesome. Drip some of the strongest white vinegar you can find in there and see what happens. If you can get it loose enough to wiggle fairly freely, the neck can be levered out of the block using the top over the block as a fulcrum. The worst likely scenario there is that the fingerboard pops off.
     
  12. Stu Elston

    Stu Elston

    Apr 25, 2004
    Knoxville, TN
    Between the post previous (where I speculated that the glue might not be hide) and yours (KFS), I realized that water might either evaporate or become chemically involved with the glue as it dries/cures, so I took another glob and a roughly equal volume of water, and the combination dissolved/melted at around 160 F. So I take it back, it looks like it might be hide glue, after all. My experience with hide glue is limited to having to built a mountain dulcimer with hide glue, i.e. from the flake state to a cured joint, but I've never tried the reverse.

    So, is it correct that a 'glob' of cured hide glue takes a little H20 as well as heat to return it to a fluid state? Seems reasonable, but as others have suggested and I freely acknowledge, I'm a bass-repair-virgin.

    Also between then and now, I have found that I can work/worry a thin (artist's) palette knife, which measures 0.010 - 0.012" thick at the tip, into the glue joint space along the sides of the neck join, in many places to a depth that looks consistent with the depth of the mortise. Once or twice during this, I heard a (promising? scary?) pop, probably the glue joint cracking? The neck is looser now, and when I wiggle it, I see less of the parallel, segmented, diagonal cracks within the wood on the sides of the heel. This seems to me like progress, but there is clearly a ways to go, and what do I know??
     
  13. That popping or cracking sound is the glue letting go. And it's a very good thing.

    You can make a simple steam rig with a hot plate, laboratory glass, stopper and rubber hose. Be careful, because steam and old plywood are mortal enemies.
     
  14. james condino

    james condino Spruce dork Supporting Member

    Sep 30, 2007
    asheville, nc
    With that much education and a healthy curiosity, you've got the perfect credentials to join the other luthiers I know who spent enough money to buy a house learning something they did not want to do for the rest of their lives so now they now make $19,000 a year as a luthier working three times as much as before.....!
     
  15. Matthew Tucker

    Matthew Tucker Commercial User

    Aug 21, 2002
    Sydney, Australia
    Owner: Bresque Basses, Sydney Basses and Cellos
    Also may I repeat that a neck reset with block replacement and button repair is a complex job even for someone who has done it plenty times before.

    I think you should go see James. Even if you don't leave the bass with him, you'll learn stuff.
     
    Stu Elston likes this.
  16. Stu Elston

    Stu Elston

    Apr 25, 2004
    Knoxville, TN
    Yep - I agree - working on visiting James.
     
  17. Stu Elston

    Stu Elston

    Apr 25, 2004
    Knoxville, TN
    Update: I drove through the Smokies, from Knoxville to Asheville, yesterday, to visit James Condino and to get an evaluation of my bass and its problem. Once he got out his steam generator, it was a matter of half an hour and we had this:hyper::
    CB-neck-free-at-last. This is on James's workbench. The neck itself seems to be in great shape and will take a bit of cleaning up - that will be my problem - before we consider how to trim the face of the tenon to achieve a better neck angle/bridge height. Cleaning up the neck block and mortise is also my assignment (shown on my worktable; I was too excited being in James's shop to think to take more pictures):
    CB-neck-mortise. The major problem will be getting the face of the mortise flat. There is a lot of crud to clear away, including yellow glue from some previous repair. Note hole near the center of the mortise. It looks like once upon a time there was a screw through the neck block into the heel of the neck: CB-neck-tenon-face. (Sorry, it's hard to tell Eloise she can't be part of the action). Maybe the screw (which wasn't actually in the hole and must have been part of some earlier work) was just used to keep stuff aligned and tight while glue was setting - it clearly wasn't a very large screw; maybe a #8. Here's a closer look at the face of the neck block/mortise (not pretty): CB-neck-mortise-close. Very little cleanup has been done so far (obviously); I've ordered a steamer to help and it should arrive tomorrow. There is yellow glue in spots, which James suggests might yield to some vinegar.

    The good news is that the neck is sound, the body seems more or less sound, and I have a pro to consult and help when I get in trouble:thumbsup:. Also - there wasn't a ton of hardware in the neck joint!

    The bad news (IMO) is what appears to be cracks partway down the center of the face of the mortise and to the right (bass) side. My impression is that James thinks that he/we can fix this without replacing the neck block. We didn't talk a lot about the detail of this while I was there, so I can't speak to what he might have in mind. I worry about the fact that the plane of the mortise face seems deeper than the edge of the top plate (notice the shadow) - I suppose that edge could be cut back a bit, but I think we removed a shim from the face, so we'll need another shim, or what? Maybe deepen the face enough to inset a piece that's too thick to be considered a shim, and thick enough to permit using dowels to tie the sides of the crack together? This feeds into what I can get away with as I clean that face up - how careful do I need to be in removing wood? (very!) The face clearly needs flattening . . .

    Interesting side note: I'll probably always be uncertain as to the provenance of this instrument. James had a neck heel with at most 6 or so inches of neck length that he said was from a German shop bass (he mentioned Pfretzschner) that had shape and size uncannily identical to my neck heel. Same taper of the tenon, same shape of the toe, same break-shape from heel to neck. But then, they probably turned out thousands of such necks.

    A very worthwhile way to spend part of a Saturday afternoon. Thanks, James, I learned a thing or three!
     
  18. james condino

    james condino Spruce dork Supporting Member

    Sep 30, 2007
    asheville, nc
    Late response; I just got back in town from the Guild of American Luthiers convention. The nerdfest was ok, but the week before on a sailboat in the San Juan islands and then climbing Mt Rainier after was a whole lot more fun!

    Stu was great to have in the shop for a couple of hours- patient, easy going, and fun to chat with. He forgot to mention that while we worked away I had several other customers show up and get in line. They mentioned their band, so instead of sitting around, I prodded them into playing a full set of nice traditional bluegrass on a couple of my other instruments while we worked away- classic North Carolina Saturday afternoon....

    As for his bass- it has a few issues, but it was in better shape than I expected and there is a back story behind it. With a bit of love and a 1/4 pound of hot hide glue, there is still another half century or two of great music left in that old bass.
     
    Last edited: Jul 25, 2017