Neck Repair Splines

Discussion in 'Guitar Building' started by Jim_E, Apr 10, 2014.

  1. Jim_E

    Jim_E Active Member

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    If anyone is interested I'd like to discuss the pros and cons of repairing a Gibson style headstock break using splines to add strength - do they really add any strength, if so is the amount of strength based on how they're cut and where they're placed, etc...
     
  2. Fret Hopper

    Fret Hopper Member

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    You should check out this thread over on mylespaul, where BCR Greg is doing repairs to one of Jon Bon Jovi' s guitars. BCR Greg is truly a master of neck repairs. In this example he uses neck splines to reinforce the neck repair.

    Repairing Jon Bon Jovi's Les Paul Classic. - MyLesPaul.com

    You might check out BCR Greg's other repair threads. He has done some truly unimaginable repairs, and has results making you wonder "where is the repair?".

    Hope it helps answer your questions.

    Fret
     
    Last edited: Apr 10, 2014
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  3. poro78

    poro78 Well-Known Member

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  4. Adam

    Adam Well-Known Member

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    I've done Gibson neck repairs without splines, just use a high quality epoxy (24hr cure type). Haven't had one come back yet.
     
  5. Duplex Dave

    Duplex Dave Active Member

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    Sometimes splines are little over-kill, adding more work than necc. If there is a good amount of surface area like the LP in the MLP link epoxy will be more than adequate, like Adam said. I prefer the West Systems slow cure. If a headstock will break again it will not be along the repaired joint (if done correctly).
     
  6. Jim_E

    Jim_E Active Member

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    While you guys are saying that they're overkill I'm wondering if they do anything at all the way I see some of them done. To me it depends on the section size of spline, the grain direction, how they fit the mortise, glue etc.

    I see a lot of spline jobs where the mortise is shallow, grain is the wrong direction and it doesn't make any sense to me as there is little to no strength added.
     
  7. Jim_E

    Jim_E Active Member

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    Well that’s interesting but I think it demonstrates what I see most of the time – those mortises don’t look parallel sided, flat or deep enough, in other words the question is how much strength are you adding – the splines would fit poorly and the grain direction on them looks off by 90 degrees, the extra piece on top of the splines is for what? then slather it in epoxy?

    I have a little experiment I’m cooking up to see how much a weight 3/8” wide by < 1/4” thick (50’s Honduran mahogany) spline can actually take before it snaps like a toothpick, results to follow...
     
  8. BWGuitars

    BWGuitars New Member

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    I dunno, you're arguing with a dude that has like 35+ years and a lot of respect repairing vintage instruments. Plus it doesn't sound like you read through that link but scanned through the pics...



    Composite construction. It's not the strength of the spline itself, but the strength of the whole thing once the spline is glued into place. Laminated construction is quite strong, and is a function that isn't predicated on the strength of the weakest component in the mix.
     
  9. Jim_E

    Jim_E Active Member

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    Well thanks but I'm not arguing with anyone, certainly not someone on another site because that isn't my link and I'm not talking to him, we're here and discussing the pros and cons, remember... and when we're talking about 35 years experience that's quite a coincidence as I'm just now in my 35th year.

    Composite construction indeed, how about you wait until you see what I have to offer toward that end before you start dissing the idea of testing? I'll be sure to take the composite angle into it.
     
  10. BWGuitars

    BWGuitars New Member

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    I'm always interested in further testing ideas in lutherie, but the way you framed it seemed relatively confined to just the strength of the spline itself, not the spline as a means of adding strength to a headstock repair. In this application, the strength of the spline itself has little bearing, and is more about (as you mentioned) the grain orientation, fit of the joints, etc.

    If you take ALL the factors into account while testing, I'll be looking forward to what you have cooking up in regards to the tests! :)
     
  11. Jim_E

    Jim_E Active Member

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    Ok so here's the plan, feel free to comment;
    I have 6 pieces of poplar cut to 2 1/2" x 6" x 3/4" thick, each has two dados cut on the tablesaw that are 1/4" deep x 5/16" wide, this is to approximate the section size what's left of your typical spline when the repair is complete.

    I also have six perfectly fitted splines which I'll trim flush after gluing them in. They are 50's Honduran, I can tell you that as I bought the lumber myself in the late 70's and it had been in someone's shop for many years prior to that.

    I have 3 complete test pieces each with the grain of the splines oriented 1 of 3 ways - vertical, horizontal and rift.

    The object is to isolate the two splines and see exactly what they bring to the equation, to find out how much extra strength two glued in splines add to the repair joint.

    To do this I plan on gluing the splines into the dado's but not gluing the poplar end grain - so that the two pieces of poplar are joined by the glued in splines and nothing else.

    I'll test the strength by using a machine head and a top E string to see if I can tune it up to standard pitch, if any of them don't break at standard pitch then it'll be time to see exactly how many pounds of pull it does take to break the joint and which grain
    orientation takes the most load.

    The hot hide glue is cooking right now, 48 hours in the clamps and I should be ready to report back shortly after that...

    [​IMG]
     
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  12. BWGuitars

    BWGuitars New Member

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    Interesting.

    That should give a good idea of how strong the spline itself is, and whether or not the spline will break before the glue will (not that it needs to be tested, the hide glue will likely be much stronger than the spline itself).

    I would recommend a second round of testing, aiming towards the idea of a composite strength test next.

    I would prep out 2 angled joints, one glued together surface-to-surface, then another glued surface to surface, but WITH splines in the mix. Then test how much force is necessary to break each of the test joints.

    That should tell you how much added strength (if any) the splines provide when simulating a headstock break being glued back together without splines and with splines. That's what we really need to know at the end of the day.

    Attached is a quick sketch of what I'm talking about.
     

    Attached Files:

  13. Jim_E

    Jim_E Active Member

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    Well that's also an interesting proposition that may give a different viewpoint, but I'm not sure it's necessary, thinking about what the added strength of the spline is, I think isolating the splines is the most straightforward way to answer the question.

    To be clear, when I glue up the test pieces I'll clamp the poplar pieces end to end (dry) and then glue in the splines so that the poplar joint is real tight and the splines are fully supported along their length.
     
  14. BWGuitars

    BWGuitars New Member

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    That will only show how strong the spline is, not how much added strength they add in a neck repair which is what it seems like you're really after. All the factors in a neck repair should be taken into account, including the interaction of the added splines AND a simulated neck repair.
     
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  15. Jim_E

    Jim_E Active Member

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    IMO the strength of the spline (when glued into a mortise and fully supported) is a good representation of how much strength they add to a joint.

    If the splines are glued in to the test blocks and fully supported then we've simulated their position in the repaired headstock and we're simply reducing it to the strength of a spline and therefore answering the question of what the spline brings to the equation in the most direct manner.
     
  16. BWGuitars

    BWGuitars New Member

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    I still disagree, but I'm still looking forward to what you find out with this test :)
     
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  17. Jim_E

    Jim_E Active Member

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    I clamped the poplar blocks end to end, dry, then glued (hot hide) and clamped the splines into place, without getting any glue on the poplar endgrain, so that only the splines are holding the two blocks together and so that we’re only finding the strength of the splines themselves. I glued them up and left the pieces in a warm room for 48 hours.

    [​IMG]

    Grain direction wise, the splines are glued in so that they are the equivalent of flat, rift and quarter sawn – one sample for each grain direction, all cut from the same piece of wood.

    I flushed them up so that they’re 1/4” deep x 5/16” wide, this I think fairly approximates the section of your typical finished spline, you see them lots that aren’t 5/16” wide and many not even 1/4” thick at the shallow end, so it’s seems generous to me.

    [​IMG]

    I installed a ping tuner head at one end, clamped one side of the block at an angle and strung it up with an E string (.052).

    [​IMG]

    [​IMG]

    I was sure going into this that I wouldn’t be able to tune that string up to E before I got a face full, and it was pretty funny trying to wind the tuner with my arm outstretched like I was diffusing a bomb, but I was able to tune all 3 test pieces up to F sharp (which is as far as I dared to) with no issues, no crackling or any other signs the wood was near the failing point.

    On to the good part, just how much does it take to break the spline? I decided to clamp one end of the test pieces to the bench and hang weights off the other end.

    First I clamped them down with the splines facing up. with the 90 degree joint in the poplar block this means the weight is putting the spline under tension, pulling on it more or less the way the strings would when the spline in place in a headstock repair.

    To my surprise, with all 3 samples I was able to hang 100 pounds of weight before I observed movement between the poplar blocks, at which point I stopped adding weight to preserve the samples for what I figured would be the final test.

    Then I clamped the first one to the bench with the splines facing down, I don’t think you can really call this “compression” of the spline, as in the opposite to what was “tension” in the last test, but it’s definitely applying force in the opposite direction – opposite to the string pull.

    The first test piece flexed wide open and barely held 10 pounds, it snapped when I added another 5 pounds.

    [​IMG]

    So, with the other two pieces I went back to see what it would take to break them with the splines facing up, loading them in the same direction that the string pressure would. Both pieces, which had previously held 100 pounds before they showed signs of movement failed at 120 pounds.

    [​IMG]

    So what I take from this (and it obviously only relates to this micro sample), is that if;

    (a) the mortises are well cut, and by that I mean flat and parallel sided, with a flat bottom at 90 degrees.
    (b) the splines are well cut fit and properly and tightly to all 3 sides of the mortise (grain direction doesn’t seem to make much difference, maybe 10 percentage points).
    (c) the spline (where it crosses the break) has a minimum section size of 1/4” x 5/16”.
    (d) the glue is stronger than the wood.

    Then – these splines can handle about 100 pounds of pull, from the direction that the strings would place the load (spline on the backside of the headstock), applying force the opposite way, they break with less than 15 pounds of pull.
     
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  18. Jim_E

    Jim_E Active Member

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    What... isn't someone going to at least criticize my method or me personally or something?... can of worms perhaps?
     
  19. BWGuitars

    BWGuitars New Member

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    I already voiced my thoughts.

    I liked your test, hence liking your post ;)
     
  20. rusdfh

    rusdfh New Member

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    I have repaired many Gibson headstocks (50 or so would be conservative) most of which were simply glued with original tightbond and clamped. This all happened in the 70's. This approach worked for me if, and its a big if, it was a clean fresh break, all the wood was there and the neck would go back in place cleanly. In others words nobody jacked with it and no big chunks fell out. The tightbond didn't creep and some came back after being broke again but not at the original glue joint. BCR does repairs that are well outside this criteria and makes guitars that simply weren't worth repairing in the 70's playable again. We did reinforced headstock and neck repairs on valuable guitars but you could buy another old Les Paul for $350 or go to Manny's and buy a 59 for $2500 so a lot of stuff just got trashed. Dug your data and test method been a lab rat myself for about 35 years
     

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