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Thread: Washburn Bowl back neck re-set

  1. #1

    Default Washburn Bowl back neck re-set

    I am currently working on an American Conservatory (by Washburn) bowl back mandolin that needs a neck re-set.

    The instrument came apart easily with no issues or damage.This is a mandolin without a dove tail joint, but instead has a fairly wide dowel which fits into a corresponding hole in the neck block. I had originally hoped that just removing the neck and cleaning and re-assembling everything might work, but clearly I'll need to re-adjust the neck angle as well.

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    So, here is where things get confusing. The dowel is solidly glued in place to the neck. When I manually re-assemble the parts, they fit well, but the neck will still need to be angled back to make it playable. It seems to me that I'll need to adjust for the shift in the angle of the dowel once I re-angle the neck heel. I can imagine doing that by removing material from the top of the dowel end and adding material to the bottom of the dowel end; perhaps by sanding the top a bit and adding an appropriate amount of veneer to the bottom. In my rather crude diaphragm below, the red parts are where I would need to remove material, but in order to keep the dowel fitting tightly, I'll need to add additional material at the blue side of the dowel.

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    I sure would appreciate any insights folks with experience in this can share with me on the proper way to accomplish this.

    Thanks for any help you can give me!

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  3. #2
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    Default Re: Washburn Bowl back neck re-set

    What about changing the interior contours of the mortise/hole? (Focusing on the yin rather than the yang, in other words.) It seems like that could be a more stable repair than altering the tenon. Or... glue a new dowel into the body as a plug, then jig up the body on your drill press and make a new bore at the correct angle. It looks like you need one or two degrees of adjustment at most.

    This could also be a good time to build in some kind of a keyway to reduce future movement.

    (This advice is worth exactly what you paid for it.)

  4. #3
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    Default Re: Washburn Bowl back neck re-set

    I haven't done one exactly like this, but . . .

    1. Rather than using the guitar oriented techniques such as removing material at the bottom of the heel, you might instead consider installing a tapered shim to the face of the heel. This is because if you remove material from the face of the heel, you will be reducing its footprint and you will no longer have a smooth joint between heel and body. My first choice wood be rosewood. It's more work, but it will look better cosmetically. The final profiling would have to be done very carefully and cleverly-- a curved mini-scraper with a tight radius or a masked sanding block with a rounded surface might come in handy. You can touch up with violin varnish and/or shellac.

    2. Also consider whether it would be easier to remove material and add a shim to the dowel or whether it would be easier to work on the hole in the neck block. If it were me, I would re-work the hole.

    You'll have to get inventive to get a good fit either way. If you work on the hole, a slightly smaller piece of dowel with sandpaper glued to it might come in handy. I would be more inclined to do the work by hand than with a drill press. The better banjo people use a horizontal boring machine and a sled, but except for those who do a lot of banjo dowel resets, most of us aren't tooled up for that sort of work.

    3. Oh-- plan C: If the fit is good and the geometry is not, re-assemble the neck joint as-is, pull the fingerboard, and adjust the geometry by installing a long tapered shim to the bottom of the fingerboard. It might deliver you the best cosmetic results if you do it well. The more I think about it, the more I like the idea. It might be end up being the easiest and best looking solution in the long run.


    One thing that I'm sure of is that you will not want to remove the dowel from the neck heel.

    If anybody has better techniques, I'm all ears.

    Fun and games. However you end up doing it, let us know how it turns out and what you have learned.
    Last edited by rcc56; Nov-19-2022 at 3:08pm.

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  6. #4
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    Default Re: Washburn Bowl back neck re-set

    "3. Oh-- plan C: If the fit is good and the geometry is not, re-assemble the neck joint as-is, pull the fingerboard, and adjust the geometry by installing a long tapered shim to the bottom of the fingerboard. It might deliver you the best cosmetic results if you do it well. The more I think about it, the more I like the idea. It might be end up being the easiest and best looking solution in the long run."

    Definitely a vote for Plan C here. Great idea if everything else lines up.

  7. #5

    Default Re: Washburn Bowl back neck re-set

    Thanks very much, everyone. I appreciate hearing things from the mandolin world viewpoint!

    rcc56, great explanation of the problem! The current fit is very tight so I'm also leaning towards plan C. As I recall the fingerboard is rosewood, probably Brazilian, and I should be able to take it off with little or no damage. I also appreciate plan A, and will ponder that as well, though I expect that would involve some world class fitting.

  8. #6

    Default Re: Washburn Bowl back neck re-set

    Having done “C” twice, once on an American Conservancy bowl back, and about to do it to a zouk, I must have made the major mistakes and now learning the minor ones. “C” is a good bet.
    First, the dowel in the neck heel may actually be part of the heel, not glued in. There’s hardly enough depth there for a dowel, and it can easily be milled into that shape.
    Second, the shim idea is much more controllable than sanding a tiny angle in the body. And can be revised. Shim at the fingerboard, even easier.
    And: The fingerboard is thinner than on later instruments, is very old and dry, and may not come off in one piece, as the fret cuts are relatively deep, and even inlay graves deeper (yes, I had a break at one of these). Go easier and hotter.
    Shimming under the fingerboard is also controllable, adjustable and can also correct any flatness issues that have developed, but since the board is meant to sit flat on the soundboard, it is going to look a little different in that area, so prepare for clean and finished edges. You don’t have binding, which is good, because replacing same is also not going to cover the shim. When you reassemble the board, clamp it under something very flat, full length as the tiny frets won’t stand much correction later.
    And another mistake I made: unlike a dovetail or even a rectangular tenon, the dowel doesn’t locate the board in rotation angle: the fretboard does, so unless like me you are belt and suspenders, make sure that the board winds up decently untwisted with respect to the soundboard. Belt and suspenders is adding another dowel or metal hardware from the inside. For a weak, cracked neck block, I added another layer of wood as a bulkhead, plus a bolt.
    Enjoy!

  9. #7
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    Default Re: Washburn Bowl back neck re-set

    You can use a 1" x 5" 25 watt heat blanket, available from McMaster-Carr or MSC Industrial to lift a mandolin fingerboard. You can use the same heat blanket to lift flat top guitar bridges. A Harbor Freight router speed controller will work for a temperature controller. If you work on guitars often, you might also get a 2" x 5" 50 watt blanket for guitar fingerboards. Sometimes it helps to use just a drop or two of water on your lifting knife.

  10. #8
    Full Grown and Cussin' brunello97's Avatar
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    Default Re: Washburn Bowl back neck re-set

    Thanks for posting this project!

    It is interesting to see the dowel joint on your AC. The one I have here awaiting its revival has a dovetail neck joint.

    I'd encourage consideration of what is being called "Plan C" in this conversation.

    I have done this to numerous US bowlbacks (Martins, L+H labels, Washburns) and a range of Italian MOR bowlbacks.

    Not a lot of options with the Italian bowlbacks due to their intergral neck / neck block construction.

    Another good thing for your case is that US bowls had far thicker fretboards than the Italian bowls of their era.

    Many of the MOR Italian bowls had their frets cut after the fretboard was attached so with their particular thinness, the fretting cut went right through them into the neck proper.

    Removing the fretboard can result in a lot of separate pieces.

    I've also tapered replacement fretboards to do the job in one step on both US and Italian bowls.

    I made a simple jig which allows me to taper fretboards or shims sanding against a shooting board at whatever shallow angle is required.

    That's been my SOP on MOR Italian bowls as the fret spacing and intonation on these can be muy sketchioso.

    Resolves two problems at once.

    I've been able to resuse the old brass frets in the preslotted repleacement fretboards.


    Another positive of the "Plan C" method, is that if you can cleanly remove your AC fretboard, nothing you're doing precludes more radical neck adjustment strategies at the dowel / hole.

    Have fun and keep us updated on your process!

    Mick
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  12. #9

    Default Re: Washburn Bowl back neck re-set

    Again, thanks for te excellent info, everyone! I've been infatuated with bowl backs for some time since excellent quality instruments are frequently available for very low prices since most folks don't know how to deal with them. So glad to see so many on this forum have experience with these undervalued instruments.

    Here are the latest update...

    I definitely agree with what most folks have stated, and have moved forward with plan C.

    The fit with the neck was an uncommonly good fit, so I started by using HHG to re-glue the neck using "big rubber bands" to clamp the neck into place. I did this with the fingerboard still attached, though I was careful to keep the glue away from the fingerboard extension so it would be easier to remove. This helped keep the neck properly rotated as it all came together as suggested above.

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    The next day, I heated the fingerboard old school style, with an old iron, being careful to avoid scorching the Brazilian Rosewood fingerboard. I do have the LMI temp adjuster and the small 1 X 5 bridge heating pads, but have found the iron heats very evenly through the frets and the fingerboard came off clean and easy with no damage.

    I then measured the needed shim by adding thin pieces of wood under the fingerboard extension to find the correct thickness. I have a variety of scrap hardwoods around and found that a thin piece of cherry was almost perfect thickness, and since I plan to stain it to match the rosewood anyway, I went with that (none of the rosewood scraps I have matched the color anyway and were much thicker). I cut a piece slightly larger than the fingerboard and thinned it to a long tapered bevel on a belt sander using a stick with double stick tape to hold it in place. Once it reached the appropriate bevel (full thickness at the body end, down to nothing at the headstock end) I used HHG to glue it to the back of the fingerboard (previously cleaned and leveled). This left me with a fingerboard with a slightly wider wedge glued to the bottom. I'll sand that to match the dimensions of the fingerboard before glueing it all together.

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    I've cut everything so the final measurements should be about 1/16th "overset" to allow for potential bowing of the neck.

    Let me know if anyone see's potential problems with any of this and thanks again for your advice!

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  14. #10

    Default Re: Washburn Bowl back neck re-set

    I've been tied up lately, but finally got around to completing this project. I was able to glue the shimmed fingerboard with no problems. Everything fit back together well and the shim adjusted the angle of the fingerboard perfectly. I used a bit of tobacco brown dye to color match the shim under the fingerboard extension and did some minor finish touch up around the fingerboard.

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    The nut was the original ebonized maple one and was damaged so I replaced it with a new bone nut. The frets were fairly well worn, but I was able to level them and crown out the divots.

    The original bridge had been shaved down from the bottom over the years as the action rose so I glued on a thin piece of ebony to the bottom return it to it's original height.

    After a new set of ultralight strings (9-32) and a re-seating of the bridge feet, the action came in at .013 at the 1st fret G and .011 at the first fret E string. It's got a great tone, woody but full and clear, and boy is it loud!

    I am pleasantly surprised at how well this came together. Using the shim was definitely the way to go. Thanks very much for all the great advice!

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  16. #11
    Registered User Tavy's Avatar
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    Default Re: Washburn Bowl back neck re-set

    Good to see this one finished off and getting played again - not sure about the size of that headstock tuner though

  17. #12
    Full Grown and Cussin' brunello97's Avatar
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    Default Re: Washburn Bowl back neck re-set

    Nice work all around!

    I'm glad this came together so well....another vintage bowlback saved for the next century.

    I agree with you: the project on these Washburn bowls can be astounding.

    I appreciate all the photos and step by step description.

    Does that bow mean this will be a wonderful gift for someone?


    Mick
    Ever tried, ever failed? No matter. Try again, fail again. Fail better.--Samuel Beckett
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  18. #13

    Default Re: Washburn Bowl back neck re-set

    Congrats; award yourself a nice ribbon! Oh, you did! So how does it sound? My fancier AC is beautiful, but not too exciting, but the second one, lesser trim level, really is nice; clear and crisp with a solid low end. Both are holding up after the repairs. Hope I don’t feel obligated to keep getting their relatives just to understand what makes one better than another.

  19. #14

    Default Re: Washburn Bowl back neck re-set

    Well, the bow is just because I planned to return it to it's owner a couple days ago and the holiday spirit just overcame me!

    This has a surprisingly full tone with a strong low end and a clear, bright, high end floating on top. Right now it's just a bit mid-rangy because it hasn't been played enough to break it in again. I expect it will open up the more it gets played. It's almost astonishingly loud. I'm surprised at how much I like the sound.

    While this one was a repair, I have quite a few I've bought over the years simply because they were beautiful, well made instruments at dirt cheap prices but in need of serious repair. With this project under my belt, I think I'll feel more confident to take on another one.

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