Tell me if you've heard this one before... my old Kay has a cracked heel

Discussion in 'Setup & Repair [DB]' started by Raymond Kallas, Oct 18, 2016.

  1. Hello All.

    I have a old 53 Kay TV-21that I'm restoring. I usually work on guitars, but I am a bass player and I've always wanted to work on a double bass. My Kay is in fairly decent shape except for the heel break. It's kinda of ragged, not a smooth break, but seems like it will fit back together fine. Since this is the original neck I want to try and save it.

    I've spent probably several hours looking at all the "cracked heel" posts on TB and I've concluded that there are 2 schools of thought on this matter.
    1) Using epoxy and lag screws is the best way to repair this.
    2) Using HH glue and a wooden or bamboo pin is the best way to repair this.

    I use HH glue to build and repair acoustic guitars so I like this approach. And using a wood pin seems sensible as the expansion/contraction factor is going to have less of a variance than metal. I'm sure I have the ability to do this repair, I just want to be sure I'm using the correct method.

    Also, the neck had a very sloppy fit in the mortise. I've been able to add some .4mm Poplar shims along the sides of the mortise and that seems to have improved the fit, but I still have enough gap at the bottom between the tenon and mortise.

    I'm including some photos of the neck heel now that I've gotten it to a chalk fit.
    Maybe one of the professional luthers here can offer some insights or wisdom on this?

    All input is greatly appreciated.

    Ray Kallas
     

    Attached Files:

  2. I'm far from a professional luthier, really just a monkey with a glue pot, but I've done that repair myself and might have something intelligent to say.

    The reason Kay necks always break is half because they're not cut on the quarter and half because the neck sets are riciculously sloppy.

    If you give a halfsawn neck air space to collapse into if the bass falls over, it breaks every time.

    Since you're determined to use the original neck, you'll need a good tight shim or three to make the neck joint tight, and set it with strong hide glue.

    As for the heel break, HHG might not be the medicine. The last one of those I did failed twice while it was my personal instrument in high summer so I went heavy using hide glue and a countersunk lag bolt, which some frown upon because wood moves and metal doesn't so it might work loose, and then reset the neck as normal.

    West Systems T-88 epoxy and urethane are also options for permanent glue joints. Not neck sets. Ever.
     
    spaghettiwestern and Ortsom like this.
  3. Thanks Kung Fu,
    Yeah, I'm aware of the flat sawn neck wood Kay used. It's a shame really. Imagine if the Kays that remain today actually had good necks. Wouldn't that be nice! Amazingly enough, mine is still very straight.
    I've already done the shims in the mortise and it's a nice tight fit, but there's still enough room for the glue. Just curious, did you use 192 gram strength HH glue on your failed repair?

    Ray
     
  4. Ortsom

    Ortsom Inactive

    Mar 23, 2016
    The shear strength of a well executed HHG wood-wood joint is as strong as they come, under suitable conditions. And potentially serviceable.

    Peel strenght-wise, however, this may not be the case; there may be stronger alternatives (in epoxy & PU glues). I cannot find reliable info on that. The top part of that break is exposed to a peel load: with the heel fixed at the button, the top part is in tension and the bottom part in compression. A proper fixation along the entire length of the heel reduces the load on the break, but a peel component remains.

    Of course, once repaired, that broken heel does not need to be serviceable, you just want the pieces to stay together (unlike the heel-to-block joint, that should be serviceable). That's where a lag bolt or something else with a high tensional strength (bamboo? pieces of thread?) comes in. BUT: HHG does not stick to steel, and using HHG humidifies the wood (causing later shrinking during drying). If you use steel, better not with HHG (use epoxy or PU). Of course you can do the lag bolt after the HHG joint has fully dried (but the mechanical action of a bolt may cause cracking). Bamboo could work with HHG, but I never tried that and bamboo has a quite impermeable skin that might not impregnate with HHG.

    And I'm not a luthier either, just a baboon with a slide ruler and a clamp. Maybe one of the real luthiers encountered elsewhere could chime in and positively contribute.
     
  5. robobass

    robobass

    Aug 1, 2005
    Cologne, Germany
    Private Inventor - Bass Capos
    No. approach #3) HHG with screws. You can remove the screws later, but I find that screws are a simple and effective way to clamp the joint tightly, so that you can get good adhesion with HHG. A tight joint is less important when using epoxy. I've used this approach three times and all were successful.
     
  6. Interesting. Once you remove the screws, do you fill the holes with wooden pins?

    Ray
     
  7. robobass

    robobass

    Aug 1, 2005
    Cologne, Germany
    Private Inventor - Bass Capos
    I just left the screws in.
     
  8. Hi Robobass,
    I saw in another post where someone used 3 screws, and I've seen the one big lag screw approach.
    What size and how many screws did you use for your repair, and what was the gram strength of the HH glue?
     
  9. I hope so too. I'm just starting out as a luthier and I've never tackled this kind of repair before.

    Thanks all!
     
  10. robobass

    robobass

    Aug 1, 2005
    Cologne, Germany
    Private Inventor - Bass Capos
    Raymond,
    I think I used two #6 drywall screws, and whatever glue my luthier gave me. IMO, the most critical part is drilling the pilot holes really accurately.
     
  11. james condino

    james condino Spruce dork Supporting Member Commercial User

    Sep 30, 2007
    asheville, nc
    Ray,
    Call the shop and I'll talk you through how I approach this far better than I can type; Facetime is also a great option. I pretty much have at least one old broken Kay neck on the workbench every day of the year for the last decade and a waitlist dozens deep. Like them or not, vintage Kays are fantastic job security where I live!

    J.
    www.kaybassrepair.com
    www.condino.com
     
  12. Hello James,

    I sincerely appreciate your offer. Facetime works for me. I'm assuming you'd like to see my heel break.
    I'm in the PST zone so I did this on my lunch break, it would be 3 pm your time. Or before work, which is 8am for you. Another option is if you're in the shop on Saturday, any time of the day is good for me.
    Let me know what works best for you.

    Thanks!
    Ray