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Some questions on gluing and clamping

Discussion in 'Setup & Repair [DB]' started by gandalf1, Jan 3, 2013.

  1. gandalf1


    Feb 28, 2008
    Stony Brook, NY
    Hi All,

    I’ve learned a wealth on this forum about hide glue itself, including strength, preparation, benefits, sources, etc., but I’m having trouble finding information on the actual glue-up and clamping process. Thus, a few simple questions, hopefully easy to answer for those that do this daily.

    1. Should glue be applied to one or both surfaces to be joined?
    2. Clamping sequence. Hide glue gels 1-2 minutes after it’s removed from the pot and applied. Does the final clamping need to be completed before the glue gels, or is it OK to apply glue, then hold the pieces in place as tightly as possible by hand until the glue gels (1-2 minutes), then apply the final clamps/clamping pressure over the next 2-3 minutes and let stand overnight? I can certainly see the benefit of clamping before the glue gels, but I can’t imagine getting everything clamped up in such a short time, especially for a complex or tricky clamping situation before the glue gels!
    3. What is the school of thought on clamping pressure and gaps? Is a lot of pressure desirable, really forcing the pieces together, or less (but still significant) pressure, and allowing a thin glue layer to remain between the pieces. [I know this is really a "feel" question, and is rather vague; a more proper question might be what are recommended clamping pressures, in psi, but this might not be available from the manufacturers, and is hard to replicate anyway in the shop without load sensors on the clamps]
    4. I’ve read that a small amount of liquid hide glue or urea can be added to normal (granular) hide glue to extend the setup time. Any thoughts on how much to add versus increase in setup time? Is there a limit to how much to add? How much is the final strength compromised. I'd rather not add anything if I can help it, but depending on the answer to #2, I may have to increase the gel time.

    Thoughts and advice are most welcome. Thanks all. I’m starting to get close to regluing all of the braces back into my flatback (see related thread for the woes: http://www.talkbass.com/forum/f3/repairing-braces-romanian-flatback-870011/) and just wanted to clarify the gluing sequence I should plan to use.

    As always, the wisdom of this forum is very much appreciated. Thank you.

    -Jon Longtin
    Stony Brook, Long Island, NY
  2. 1. I typically prep the glue surfaces with a thin layer of glue before the final glue-up. It seems to help the adhesion.

    2. I have successfully press-fit cleats, holding them in ace until the glue gels and not bothering with clamps. I would not try that on a structurally important components.

    3. Gaps should be eliminated to the greatest degree possible. Hide glue sucks at filling voids.

    4. Never tried it. I have heated a bass bar in my stove before fitting it to the top, which seemed to extend the open time slightly.
  3. RCWilliams

    RCWilliams Commercial User

    Apr 23, 2007
    Merriam Kansas (Kansas City)
    owner RC Williams Co. LLC
    are you gluing plates? if so, no gaps, the plates should be able to be held together dry and there should be no light visible at any point between the jointed surfaces when held up to a light source without much pressure required. you can heat the surfaces to increase the open time a little. always dry fit and rehearse the clamp up procedure a couple times if you are not used to it. never glue up in a rush, don't put anything in your glue unless you do some experiments with it first. a little granulated urea added to a batch of glue will increase the open time. a little is supposed to strengthen the glue, a little too much will degrade it. some bar clamps tend to pop up the plates a bit more than others, but it is a good idea to have some cauls set up to keep the plates in the same plane. I mix my glue to the approximate viscosity of 30n to 40 wt motor oil.

    that's my story and I'm sticking to it... till I come up with a better one.
  4. eh_train

    eh_train Supporting Member Commercial User

    Jan 12, 2004
    Owner, Stand Up Guy Basses (Repair/Sell/Buy upright basses)

    Not sure if the responses, so far, addressed Gandalf's first question (glue one or both surfaces?). I think, though others may disagree, that gluing both is a huge help.

    KFS, now that I re-read, in your point #1 you mentioned prepping the surfaces (that's plural surfaces) by sizing them with a thin layer of hide glue. This layer acts as a sealer and is left to dry before the actual joining takes place. When you are gluing "for keeps" the earlier coat of glue helps tremendously with "grab".


    Paul (Eh_train)
  5. uprightben


    Nov 3, 2006
    Boone, NC
    You can also hit the joint with some heat after clamped in order to reflow the glue. I like to do this after I've used water to clean up squeeze out, and then give the clamps another little turn after. Just be careful not to burn anything...
  6. arnoldschnitzer

    arnoldschnitzer AES Fine Instruments

    Feb 16, 2002
    New Mexico. USA
    Jon, when gluing up plates you do a small area at a time, applying glue with a thin artist's spatula. Put on the clamps immediately, then clean off any squeezed-out glue before it sets. Once hide glue has gelled, it is no longer an adhesive. There is no reason to size anything except the endgrain on the blocks. It's a good idea to join the top and bottom ends first, as the fit there is crucial. Good luck.

    Oops, just read that you are gluing the braces. Warm the brace, add a little (5-10%) urea to the glue, practice your clamp-up, grab a helper, brush glue quickly onto the brace, put in place and get the clamps on pronto. You have 40-60 seconds to get it right. If you have any question, abort immediately, wash off the glue, dry the parts and start over. When gluing braces to a flat back you need a caul underneath to spread the clamping pressure, which should be moderately strong. Ideally, glue squeezes out all over. I usually wait until the squeezed-out glue gels, then remove with the end of a small ruler.
  7. Urea? Did I read that right? Good to have you here on the boards Arnold...
  8. RCWilliams

    RCWilliams Commercial User

    Apr 23, 2007
    Merriam Kansas (Kansas City)
    owner RC Williams Co. LLC
    oops, I guess I needed to read all the way to the end, wrong blue job in my reply
  9. arnoldschnitzer

    arnoldschnitzer AES Fine Instruments

    Feb 16, 2002
    New Mexico. USA
    Yes, you read correctly. Liquid hide glue has so much urea that it stays liquid at room temperature. But this makes it prone to re-hydrating in humid conditions. If you run out of urea, just pee in the glue. That's what the old-timers did. :eek:
  10. jnel

    jnel Guest

    Dec 19, 2012
    and while your urine is a curen, you can go do something else
  11. gandalf1


    Feb 28, 2008
    Stony Brook, NY

    Thanks for the excellent feedback regarding gluing and clamping! As I expected (and feared), it sounds like everything must be have all final clamping in place before the glue gels. I think I'll put this above my workbench:

    "Thou shall maketh sure to fitteth thy joints well dry, with thine temperatures residing thus well about room temperature. Thou shall moveth quickly and with grace in thy clamping process. Thou shall bring thy full brunt of thy clamps upon thy joint before thy glue doest gel, and thou shall not hesitate to confess thy mistakes and start once again."

    Arnold/RCWilliams, thanks in particular for tips on the entire clamping sequence, urea additive recommendations, clamping pressure, and use of a caul. This is exactly the advice I was looking for.

    I appreciate the advice on gluing the top plate as well. That's going to be a whole new kettle of fish when I get to that point, and I am sure to have a bunch of questions.

    Once again, my respect for luthiers has been bumped up a notch, as these folks can make reliable joints that last decades on a daily basis.

    Next stop: shaping and tuning the braces. I'll start a new thread on this.

    Thanks again to all for the advice and tips.


    (N.B. Nice article on making cauls here: http://www.mikes-woodwork.com/Cauls.htm).

    On a parting note for urine and urea: the Romans used a heated mixture of urine and water as a bleaching and cleaning agent for those beautiful white robes of theirs. So valuable was the commodity, that ‘pee pots’ would be placed outside local clothing cleaner outfits for passers by to relieve themselves. Imagine having that gig on a 95 [SUP]o[/SUP]F day in Italy.
  12. jnel

    jnel Guest

    Dec 19, 2012

    Here, hear

    And may I propose a toast to all bass luthiers

    while you are charging your measuring cup, may I remind us all that any toast to luthiers is always a "bottoms up" ...

    To the luthiers...to the luthiers :eek:

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