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Headless four string ”Brucefied”

Discussion in 'Luthier's Corner' started by MPU, Feb 24, 2018.


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  1. MPU

    MPU

    Sep 21, 2004
    Valkeala Finland
    Bruce, this one is for you: How deep should I route the softening chambers? Is it fine if I leave something like a bit over 1/4” for the top and back? Or should the top and back be thicker?
     
  2. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    That really depends on the size of the chambers you are routing. If they are relatively small, you can leave just 1/8". For larger chambers, where the span across is 2" or more, it's safer to leave 1/4". Just to keep someone from caving it in later on.

    A simple way to do chambering is to rout a pattern of straight slots, parallel and leaving 1/4" to 3/8" wall between them. Make the slots like 3/8" wide and deep enough to leave 1/8" of the top surface. That's simple to rout and work with.

    If you make those slots parallel to the centerline, you are turning the center area of the body into a row of little parallel I-beams. As a rough guideline, think of what percentage of the volume of wood you are removing. You are weakening the body by about half of that percentage. That is, if you are removing 50% of the wood, you are weakening the beam by around 25%. The webs and the top and back surfaces are still carrying the bulk of the load.

    If you cut the slots crosswise, perpendicular to the centerline, that weakens the structure much more. That's like cutting big holes in the web of an I-beam. The top and back surfaces are still carrying the bulk of the load, but because they are thin, they could buckle. In that case, removing 50% of the wood may remove 50% of the strength. You could have structural problems. The body could bend and collapse under the load of the strings. Which is not a good thing.

    In general, you are trying to weaken the body somewhat. Not drastically. As a starting point, I'd suggest removing 30% to 50% of the wood volume from the center area of the body, leaving some ribs parallel to the centerline.

    Making the center area of the body weaker like this allows it to flex more with the strings, adding extra background harmonics. Because the length of this weaker zone is roughly 1/4 to 1/3 of the overall scale length, these added harmonics will tend to be in the mid-range. This is what we call warmth.

    The overall purpose of my structural tricks is to make the deep lows and the highs very clear, and then add harmonic warmth in the middle. The truss rod and the rigid neck/body joint make the deep lows clear. Careful mounting of the bridge and the nut make sure the highs are clear. Chambering the body brings in that mid-warmth and keeps the overall instrument from being too cold and sterile sounding.
     
  3. MPU

    MPU

    Sep 21, 2004
    Valkeala Finland
    Thanks! I’m routing slots parallel to the centerline. Pics later today.
     
    mobdirt likes this.
  4. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Yes, the slots you show on the drawing on the previous page look fine. That's the basic idea. The chambers don't need to be straight line slots, but that's just simple to do. The main thing is that you want to keep some ribs going along approximately parallel to the centerline, and not let the span of the individual chambers get too wide.

    Rout them deep enough that you are only leaving maybe 1/8" thick top and back. Obviously, you have to think and plan carefully where you are going to do some contouring on the exterior surface! You may need to cut the chambers shallower in some areas to allow for that.
     
    mobdirt likes this.
  5. MPU

    MPU

    Sep 21, 2004
    Valkeala Finland
    72564A65-2E22-48B6-85E2-726EBFA67C7D.jpeg 9C7E019C-7849-46EE-AE56-02E96D598DED.jpeg Chambers routed. I may have to deepen them a bit, depending on how thick the body will be. That’s easy and fast with screw holes as locating points. I made one template which I moved with spacers. The screw holes are in the pickup cavities so they will be routed off.
     
    MovinTarget likes this.
  6. MPU

    MPU

    Sep 21, 2004
    Valkeala Finland
    913A9801-303B-4666-B440-A537500C445B.jpeg Body halves are glued together. They are at work where I do most of the woodwork that needs machines. I brought the neck blank (three piece maple) home for truss rod installation. I made a routing jig for the first Brucerod and found it tonight. After threading the rod ends and making the anchor I’m ready for routing. That’ll have to wait until tomorrow.
     
    Last edited: Feb 28, 2018
    MovinTarget likes this.
  7. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    So, you are putting the truss rod adjustment at the heel on this one? It confused me for a second when I looked at the picture above.
     
  8. MPU

    MPU

    Sep 21, 2004
    Valkeala Finland
    Yes, adjustment at heel. That way I don’t have to worry about the truss rod when making string clamp at the nut end.
     
  9. MPU

    MPU

    Sep 21, 2004
    Valkeala Finland
    BF0A1874-EBE1-4BDA-83DE-DE833D12C970.jpeg C2C39E9B-A346-4B60-970C-9E114BED0967.jpeg Body out of clamps, thickness sanded and sanded to shape. Truss rod mounted and the neck is ready for Brucebar cavities and gluing fretboard. Hopefully I’m routing the cavities tomorrow and can glue the fretboard.
     
  10. MovinTarget

    MovinTarget Supporting Member

    Jan 30, 2018
    Maryland, USA
    Hmmm I have to check if ABM has a US distributor... I was looking at the hipshot kits headless kits for a 5 string conversion I had kicking around my head as I thought that was about my only option...

    Does the ABM system require angled mounting or can they just be mounted flat on the body?
     
  11. rojo412

    rojo412 Sit down, Danny... Supporting Member

    Feb 26, 2000
    Cleveland, OH.
    They can be flat and Allparts sells them. Well, the tuners, not the head pieces.
    (wait... they have a black 4 str headpiece and locking nut now...?)
     
    MovinTarget likes this.
  12. saved

    saved

    Aug 14, 2012
    greece
    Is the blank wood of neck longrr,or will you have the truss rod not all the way to the neck?
     
  13. MPU

    MPU

    Sep 21, 2004
    Valkeala Finland
    It’s way too long. Truss rod will be from nut to heel.
    I got the Brucebar cavities routed and fretboard glued. 541C5D00-F8F7-41C3-B0D9-CD189DD04A88.jpeg
     
    moonshinegtrs likes this.
  14. Jon Clegg

    Jon Clegg Supporting Member

    Feb 9, 2015
    Northern Virginia
    Brucification is the new sensation that's sweeping the nation.
     
    Joshua and MovinTarget like this.
  15. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Yeah, it's scaring me. I keep peeking out the windows of the Secret Underground Lab, fearing that there might be crowds of screaming teenage girls. Wanting me to modify their basses.
     
  16. MovinTarget

    MovinTarget Supporting Member

    Jan 30, 2018
    Maryland, USA
    Maybe they think you are a plastic surgeon and subconsciously omitted the "b" in "basses"....?
     
  17. MPU

    MPU

    Sep 21, 2004
    Valkeala Finland
    Keep on dreaming, you old pervert. At least here most of the bassists are bearded, bald men with beer bellies. Crowds of them behind your door... maybe you really should change your locks:)
     
    Last edited: Mar 2, 2018
    Triad and MovinTarget like this.
  18. T_Bone_TL

    T_Bone_TL

    Jan 10, 2013
    SW VT
    It's cool, they have the vicious guard dog keeping the underground lab safe. They probably actually have a whole pack of them, but Bruce is cagey enough to only show one in pictures.
    img_5593b-jpg.jpg
     
    moonshinegtrs, ICM and MovinTarget like this.
  19. MPU

    MPU

    Sep 21, 2004
    Valkeala Finland
    That beast eats beer bellies for breakfast. I’m glad I have Atlantic Ocean between me and it.
    Back to bass building; I’m leaning towards J bass pickup size. The P2 shape looks too big. It means I have to make pickups too. I’m going to make Lane Poor N’ish sidewinders.
    One question about fretting. In order to make the neck as much one solid piece as possible should I glue the frets? Dan Erlewine says gluing the frets really makes a difference. What do you guys think?
     
  20. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    I'm not completely delusional. Maybe you saw on the other thread that I recently gave a tour of the Secret Underground Lab to the local Cub Scout troop. Well, pictures got in the local Fillmore newspaper. The Fillmore Girl Scout troop saw the pictures and want in on the action. They too want to tour my shop and learn the secrets. So, I actually will have a crowd of teenage girls in my shop soon. Hopefully not jumping and screaming and wanting autographs.

    I'm also scheduled to give a talk about Building Things and Craftsmanship to a bunch of kids at the local library in two weeks. That's how Brucification will spread. Start with the local youngsters.
     
    moonshinegtrs, MovinTarget and Joshua like this.
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
    May 15, 2021

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