- Apr 20, 2009
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Getting the Facts about Ski Jumps
- Thread starter Turnaround
- Start date
I don’t know how to answer some of your questions. I have dealt with instruments with ski jumps that were as young as one year. All different kinds of strings, all different brands and models. Some had fret sprout, some didn’t. Fretted and fretless- I have dealt with ski jumps on both. Godin instruments can develop ski jumps too - my fretless Godin developed a small one.
Robert Godin’s comment is interesting- I have not heard that before and I’ve never tested that.
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I deleted my original post because I found a lot of the answers I was looking for nestled in the thread - what I was wondering primarily was whether there were factors that could exacerbate the development of a ski jump, above and beyond the beam weakness of the neck, such as:
1) Lack of humidity letting the neck "collapse" into a ski jump
2) Weaker fingerboard wood
3) Construction methods that overly compromise the strength of the neck in this critical area, i.e. theoretically the straight fret slots.
Ultimately, these might all play a role, but to what extent, it would be really hard to say without controlled conditions and a large sample. Again, thank you for this extremely interesting thread and your diligent work!
edit: Here's where I heard about the Godin thing:
About 8m50s and onwards.
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Those are good questions. Lack of humidity causes the wood cells to shrink, mostly in width. I doesn't seem likely that transverse shrinkage would cause a piece of wood to kink longitudinally.
The stiffness of the neck is a function of the stiffness of its components, including fingerboard. So a weaker fingerboard contributes to a weaker neck.
It's doubtful that the methods of cutting and shaping the wood add to the tendency for a ski jump to occur later. But the overall design may be a significant factor. A particularly thin neck, one with lesser cross-sectional area between the 12th fret and the body, would certainly contribute to weakness. Stiffening rods/bars in this critical area can help a great deal according to some of the makers I know (TalkBass member Bruce Johnson for example).
His actual quote was about the fingerboard, not the neck/fingerboard as a whole. He said that using a radiused slot for the frets gave about 30% more stiffness in the centre line of the fingerboard.
I think there is a point that could be argued here. Once the frets are inserted into the slots any stiffness that was removed by slotting the wood will be countered by the slight compression fitting of the fret tang. And consequently, when fretted I doubt that the tiny arc of space under the centre of the fret tang will diminish the fretboard stiffness by 30%. And I think its effect on the neck/fretboard assembly must be miniscule if there is any effect at all.
I think there is a point that could be argued here. Once the frets are inserted into the slots any stiffness that was removed by slotting the wood will be countered by the slight compression fitting of the fret tang. And consequently, when fretted I doubt that the tiny arc of space under the centre of the fret tang will diminish the fretboard stiffness by 30%. And I think its effect on the neck/fretboard assembly must be miniscule if there is any effect at all.
Really good points - I'd think that a multi-lam neck would probably be worth way more structurally than 0.5mm more wood in the middle of a fingerboard.
I'd be interested to see a ski jump on a Ric, as it has a few major differences from a regular Fender-style neck:
1) The truss rods run end-to-end;
2) There's a wooden "spine" running in between the rods;
3) They're much deeper in the neck than a rod that pushes against itself;
4) The neck is only 20 frets;
5) The fingerboard is super thick.
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Norlin era Gibsons are often underrated for they construction, i.e. the pancake body and the 3-pieces neck; but this might be the secret my Les Paul Custom never had any issue on the neck since 1972. Definitely the most stable neck I happened to have, only two minor setups in 48 years.
Attachments
They use cheap materials, but they're solid as heck. I wish they'd have kept the volute on the neck rather than reverting to the inferior 1950s design. Ah well, they're in the business of making replicas rather than guitars these days.
My 69/70 (Pre '70 body/post '70 neck) Gibson 335 had a volute. Even so, it split 3 different times...twice directly through the volute.
Saw this article in another thread.
The Perils of Bad Neck Shims — Haze Guitars
I seem to recall reading that article before, and if I'm not mistaken, @Turnaround challenging that guy on his assertions.
The Perils of Bad Neck Shims — Haze Guitars
I seem to recall reading that article before, and if I'm not mistaken, @Turnaround challenging that guy on his assertions.
Gerry and I disagree about certain things relating to neck shims. He's a highly qualified technician and his opinion is worth consideration. We're both right, but I am righter than him.
Forgive me if I missed it somewhere in the discussion, but is there any demonstrable difference between bolt-on and neck through as far as prevalence, or location of classic 12th fret kink? I've had a couple basses develop minor kink over the years, and they were both bolt on, but none of my through necks ever did, which may mean nothing. Intuitively it seems like neck through would spread the sudden change in rigidity you have from unsupported cantilever to bolted connection over the entire neck beam length, but my "intuition" has often proven dead wrong.
Bruce did address this in an earlier post in this thread. Don't bother to go digging for it, I'll quote it here:
"Yes, the ski jump condition can happen on a neck-thru too, for the exact same reasons, although you don't tend to see it as often. There are several reasons for this:
First, the transition of the back of the neck on a neck-thru is usually more gradual and deeper than it is on a bolt-on. It's transitioning to the full thickness of the body, rather than just the thickness of the neck itself. The wood is a little thicker at that critical area.
Second, most neck-thru basses are 24 fret, which means they have a longer fingerboard. That doesn't affect the ski jump problem much, but a 24 fret neck will usually be fitted with a longer truss rod. The anchor end is further towards the body. If it's a classic single-rod truss rod, this means that the rod is deeper in the neck as it goes through that critical transition zone. So, it's supporting more of the load.
Third, most modern neck-thru basses use double-rod style truss rods. They definitely support more of the load through that transition zone.....IF the truss rod is moderately tight. If the truss rod is loose and flopping around in there, then it isn't supporting anything, and the highly stressed wood may stretch.
So, neck-thru basses have fewer problems with ski jumps, but they still can develop them in some cases. The bad news is that, if a neck thru develops a ski jump, you can't just trim the jump and reset the neck angle. You have to actually un-kink the neck.
Ski jumps (I call them 12th fret kinks) are primarily a problem with bolt-ons, Fenders and others with similar geometry of the heel transition and the truss rod. "
Thanks Bruce.
Thanks for the reply.Gerry and I disagree about certain things relating to neck shims. He's a highly qualified technician and his opinion is worth consideration. We're both right, but I am righter than him.
Would you mind going into detail about your disagreements, or do you prefer to just leave it at that?
I wish I still had my '83 Aria Pro II SB Elite I, to take a picture of the fretboard.
It was a neck-thru, and had a very noticeable ski-jump.
And that was before I'd ever heard of the term.
IIRC, the lift occurred from about the 17th fret, to the 24th.
Gerry feels that a shim can be the cause of a ski jump. I do not. I am testing that very condition, but it is something that takes a LONG time. Check post number 134 in this thread. The test was started in Feb. 2019. As of today no distortion of the heel has occurred as a result of the introduction of a shim.
I agree with your assessment. the "12th fret kink" can not be caused by a shim at the end of the neck pocket, but a deformation of the end of the neck heel can, (but IMO, only if the neck screws are over tightened for a significant period of time) I have a 1966 Fender Mustang (guitar, not bass) with a "end of the pocket" shim, and in the over 50 years its been in there, it has not deformed the neck.
I agree with Richard. You can find cases where the end of the heel has curled up a bit; the end of the fingerboard lifted up, or the end of the heel curled upward. But it's from normal wood movement, grain lines and internal stresses. The wood curled by itself from its own internal conflicts.
But I don't buy that an end shim and screw loading caused the bending. That doesn't make sense engineering-wise. It would take a lot more force than the screws can apply to bend 3/4" thick maple over that short of a distance. To bend dry wood, you have to apply enough force to cause it to deflect quite a bit, and then hold that load on it for a while. Right to the Yield point, in engineering terms. With the end shim and screws, how much deflection can you get without stripping out the screws? Very little, nowhere near the Yield point. If you aren't loading it up enough to get near the Yield point, the wood isn't going to stretch and bend.
Out at the 12th fret zone, the string tension load is significantly bending and deflecting the neck. You can measure the deflection with a ruler. If the wood on the back of the neck reaches the Yield Point, then it stretches and the neck gets a kink.
But I don't buy that an end shim and screw loading caused the bending. That doesn't make sense engineering-wise. It would take a lot more force than the screws can apply to bend 3/4" thick maple over that short of a distance. To bend dry wood, you have to apply enough force to cause it to deflect quite a bit, and then hold that load on it for a while. Right to the Yield point, in engineering terms. With the end shim and screws, how much deflection can you get without stripping out the screws? Very little, nowhere near the Yield point. If you aren't loading it up enough to get near the Yield point, the wood isn't going to stretch and bend.
Out at the 12th fret zone, the string tension load is significantly bending and deflecting the neck. You can measure the deflection with a ruler. If the wood on the back of the neck reaches the Yield Point, then it stretches and the neck gets a kink.
