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Puzzled by Kerfed Linings

Discussion in 'Setup & Repair [DB]' started by xwtb, May 5, 2010.


  1. xwtb

    xwtb

    Aug 24, 2009
    Shawnee, Kansas
    My Kay has kerfed linings, and according to the Kay Bass info site, they all do. I haven't seen just hundreds of basses, but I take it that the Kay's construction is pretty much the exception rather than the rule.

    On the other hand, such linings are completely standard on guitars, so it seems to me the whole picture is backward from what commmon sense would tell you: you'd think the bigger, clumsier box would be the one that needed the added strength resulting from a kerfed lining's increased gluing surface.

    So is there some rationale behind all this, or is it just one of those things?
     
  2. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Do guitar makers use hide glue? I am not a luthier, but it's my understanding that hide glue doesn't have any strength unless the mating surfaces are very close together, so I am not sure that the kerfed linings will have more useful surface. Also, I suspect that the Kay linings (yes they are kerfed on my Kay too) were a manufacturing convenience.
     
  3. Jake deVilliers

    Jake deVilliers Commercial User

    May 24, 2006
    Crescent Beach, BC
    Owner of The Bass Spa, String Repairman at Long & McQuade Vancouver
    Its not about increased gluing area, its about cost.

    Kerfed linings are a factory shortcut. Kerfing just glues right in, solid linings must be bent first. And of course, the Spanish style of guitar construction is to glue in teeny blocks, one at a time! :)
     
  4. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    Very interesting-- thanks. What's the down-side to the shortcut?
     
  5. George700DL

    George700DL

    Jan 9, 2009
    Maryland
    I hate to bring up my bass build into every topic...:) That being said, I used kerfed linings on my bass, because the plans called for it. They are flipped around though - the kerfed side toward the rib - less of a chance of little trapezoids floating in the bass.

    I suspect the rationale in the plans was exactly what Jake said: to save time (no bending needed). It seemed like a good idea at the time. They do provide more surface for gluing.

    In retrospect, I would not do it again - it would have been a lot quicker to bend the strips (cutting the slots sure took some time, luckily I still have all my digits), AND they could have been made much thinner (and prettier). It's not an aircraft carrier.

    xwtb - are you getting this from the GAL plans? I'd suggest using regular heat-bent strips instead.

    George
     
  6. xwtb

    xwtb

    Aug 24, 2009
    Shawnee, Kansas
    If kerfed lining like the Kay's (which appear to be something like 3/8" quarter-round) can be bent w/o heat I can see the time- and cost-saving (assuming you have a supply of machine-kerfed strips to work with, that is!) Curiously, Kay follows up this down-and-dirty inner lining with a flat and apparently non-kerfed outer lining.

    No-- I never popped for the full GAL instructions. The short version on the plans skips the kerfing detail. My interest in kerfed linings comes from looking for a way to protect the exposed overhang of the plywood back. My Kay's edges are totally ravaged, and they're much tougher stuff than what I have for a back in my GAL-based project.

    As opposed to flat linings paralleling the ribs (in the GAL design as well as others), the Kay's inner linings offer a lot of surface in the plane of the top/back. So I'm wondering if that same-plane "shelf" couldn't be used to support a strip of non-ply material surrounding the plywood and extending across the edge of the ribs.

    George, don't you apologize for bringing up your build. As a real-world model for "lutheoretical" concepts, it's a big inspiration, to me and I'm sure to others.

    L.F.Miller
     
  7. uprightben

    uprightben

    Nov 3, 2006
    Boone, NC
    Drurb- the down side to the shortcut is that it is only a shortcut if you have a source of mass produced kerfed linings. Cutting those kerfs takes a lot longer than bending. I also find that approach to be less elegant- you end up with more mass with kerfed linings, and their shape is achieved by clamping instead of shaping them to fit well. IMHO, depending on clamping pressure instead of a good fit is how you make a bad sounding instrument.
     
  8. Eric Rene Roy

    Eric Rene Roy

    Mar 19, 2002
    Mystic, CT
    President: Upton Bass String Instrument Co.
    hmmm...I love Google. I knew I had seen a picture of the machine that cut the kerf's before.

    KerfingMachine.
     
  9. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Looks like an old lathe has been adapted to a new purpose.
     
  10. George700DL

    George700DL

    Jan 9, 2009
    Maryland
    That looks so much more efficient than my method of putting my fingers within centimeters of my table saw blade, repeatedly.

    I could easily rig this up on my lathe, but I don't plan on making kerfed strips again, ever.

    George
     
  11. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    Thanks! ;)
     
  12. james condino

    james condino Spruce dork Supporting Member Commercial User

    Sep 30, 2007
    asheville, nc
    The other huge thing to consider about kerfed linings is that if they are used alone with no outside lining, they make for a very flexible set of ribs. Take the same set of ribs and use a solid lining and it is MUCH stronger and resisitant to flexing. Reversing them so the kerf is the gluing surface helps stiffen them a bit.

    Kerfed linings are mainly a function of production speed and ease in a factory. Remember that when you are talking about Kays, they didn't just make plywood basses. At the peak of production, I believe the factory was cranking out over 100,000 instruments per year. Imagine how much production time the bean counters were able to save when you consider the idea of having to bend linings for 100k instruments vs. grabbing a flexible kerfed lining and instantly gluing it in.

    I've worked in an instrument factory and you can't imagine what it is like trying to explain things to non-musician beancounters.....imagine building $10,000 guitars and the head guy calling the shots only life experience is working in a Pepsi plant and getting the job because he did a good job with the bottled water division...:meh:

    j.
     
  13. George700DL

    George700DL

    Jan 9, 2009
    Maryland
    That part itself could be a good thing, couldn't it?

    George
     
  14. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    As far as my understanding goes, no. I'm no luthier, but I've been told that stiffening the ribs can allow the plates to vibrate in a more desirable fashion.
     
  15. George700DL

    George700DL

    Jan 9, 2009
    Maryland
    I guess this is where "optimum" does not equal "maximum".

    George
     
  16. drurb

    drurb Oracle, Ancient Order of Rass Hattur; Mem. #1, EPC

    Apr 17, 2004
    Actually, I think it does. Stiffening the ribs allows more of the energy to be transmitted to the resonant plates. That's my understanding, anyway.
     
  17. George700DL

    George700DL

    Jan 9, 2009
    Maryland
    On the other hand though, I read and (and heard) from some luthiers that ribs that are too stiff kill the volume. I think the safest statement that could be made in this regard is: there is a happy medium.

    George
     
  18. Jake deVilliers

    Jake deVilliers Commercial User

    May 24, 2006
    Crescent Beach, BC
    Owner of The Bass Spa, String Repairman at Long & McQuade Vancouver
    Au contraire James, you believe incorrectly! Kay made about 58,000 instruments total, about half of which were basses.

    Their best years were from 1949 to 1955 when they produced 3,000 instruments each year.

    Serial numbers are available at www.thebassspa.com
     
  19. james condino

    james condino Spruce dork Supporting Member Commercial User

    Sep 30, 2007
    asheville, nc
    I was always under the impression that they built huge numebrs when you combine their house brand (Kay) along with all of the others that they subcontracted. If you've got the solid numbers, I'll take your word for it. Either way, it sure looks like they had the assembly line cranking at a pretty fast pace when you look inside some of them!

    A customer of mine has told me that somewhere out in the web there is a video she has seen of Mr Rodgers visiting the Kay factory on "career day" and there are basses flying by the production line at NASCAR speed. I haven't been able to find it but I'll try to track her down.

    As for the stiffened ribs, I used to really like to build with heavy stiff ribs with the idea of keeping the vibrational energy focused on moving the top plate, but these days, across a variety of instruments and sizes, I really like the ribs to be thin and unsupported so that they vibrate all over the place.

    This is a bass forum, but I build across several different instrument sizes, from mandolin up to the bass and find a lot of commonalities across the spectrum. In the nerdy guitar world, I've had about 6 prewar Martins on the workbench in the last month and every one of them were fantastic instruments- LOUD and feistey- and they all had ribs that were approx. .050" with no reinforcements. Fragile yes, but also fantastic resonance. There is a Carleen Hutchings article where she talks a lot about bass ribs and cites an example of one at 3.0mm where the sound was completely choked and after thining them down about .5 mm the voice opened up tremendously. I'm sure we can all give examples to the contrary. If only Uncle ken was still here.... Once again- 10 different luthiers, 10 different ways to build....

    With that, I'm turning off this silly computer and headed out to play my (unkerfed, solid lining, unsupported 2.3mm ribs) bass for the afternoon....Ciao...

    j.
     
  20. George700DL

    George700DL

    Jan 9, 2009
    Maryland
    My ribs are 2.5mm, and if I ever open up the bass, I'll replace the linings with very thin ones. I like the idea of flexible ribs. I think the curves of the bouts, especially the C-bout, add plenty of stiffness as is.

    George
     

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