Getting the Facts about Ski Jumps

[Turnaround]

Further to the last post...

Using the string as a straightedge as I suggested may seem useless when trying to assess for a backbow or an S curve, but it’s not. If you keep the string fretted at the last fret and move up one fret at a time at the other end you will be able to determine where there’s a dip or a hump. One long straightedge from first to last fret is better, but you can use the string method for a preliminary assessment

 

[craigie]

Just a note of caution...
You shouldn’t use the glue line of the fretboard or the edge of the binding to determine straightness of the neck. In fact it’s not the straightness of the neck that’s the critical factor - it’s the level-ness of the frets. Under ideal conditions both the frets and the neck would be flat, but that ideal is not always achieved. The critical flatness is the frets. Sighting the fretboard glue line or the binding may offer a quick check, but it can be misleading. Best use a straightedge on top of the frets. Don’t have one? Fret a string simultaneously at the first and the last while the string is at tension and it will act as a good-enough straightedge for this kind of assessment.

This makes sense.

If the neck isn’t straight but the frets are, then there must be frets that are filed down lower than others. Not such a problem with lots of fret life but once they’ve been levelled a few times could mean an earlier refret I suppose? I guess at that point a neck planing is in order.

 

[l_iamsurfbass]

Just a note of caution...
You shouldn’t use the glue line of the fretboard or the edge of the binding to determine straightness of the neck. In fact it’s not the straightness of the neck that’s the critical factor - it’s the level-ness of the frets. Under ideal conditions both the frets and the neck would be flat, but that ideal is not always achieved. The critical flatness is the frets. Sighting the fretboard glue line or the binding may offer a quick check, but it can be misleading. Best use a straightedge on top of the frets. Don’t have one? Fret a string simultaneously at the first and the last while the string is at tension and it will act as a good-enough straightedge for this kind of assessment.

Thank you for your thoughts Richard and I agree with you especially for 78' music master case in fact I did check the fret height and although following the glue line as you say makes the humps more apparent it is much less apparent when placing the straight edge on the neck and using feeler gauges. Less apparent but still there.
Yesterday I started experimenting with the squier neck, I clamped it down and left it in a my hot garage for a whole afternoon (Here in Malta temperatures are reaching 40degrees this week) after removing it from the claps in the evening the neck is 60% better, I plan on leaving it for longer and hoping for better results. Before I use heat lamps.
Didn't take any pictures yet in the meantime this is an exaggerated caveman drawing of what my neck looks like and how I clamped it.

I clamped the neck into a forward bow at the approximate highest point in the 'S' (shown with the red arrow). I am aware that it is not the normal way to do this but I figured to first remove the 'S' hump from the 5th fret and then If I am left with a forward bowing neck to clamp it the other way into slight back bow.
Interesting fact for your research about ski jump issues, this neck spent most of its life off the guitar body with no string tension in a hot garage and truss tightened.

 

[l_iamsurfbass]

This makes sense.

If the neck isn’t straight but the frets are, then there must be frets that are filed down lower than others. Not such a problem with lots of fret life but once they’ve been levelled a few times could mean an earlier refret I suppose? I guess at that point a neck planing is in order.

I did suspect this at first however in the case of the 78 bass which is my main issue due to the obvious higher value I know for a fact that there was no fret work done in the past as it was pre-owned from new by a guy who hardly ever used it and was sat on a stand in a studio with string tension released. (probably the reason for the neck bend)
Just hoping I can save this bass as I love the way it feels and sounds and it has a really nice birds-eye maple neck & headstock.

 

[Turnaround]

Yesterday I started experimenting with the squier neck, I clamped it down and left it in a my hot garage for a whole afternoon (Here in Malta temperatures are reaching 40degrees this week) after removing it from the claps in the evening the neck is 60% better, I plan on leaving it for longer and hoping for better results.

Good approach, but I doubt that 40 degree heat won't yield results that will hold for long. I would want the heat to be held around 60 to 65 Celsius for a couple of hours. If you choose to use a heat lamp, be careful - it's really easy to burn the wood.

 

[Gigglingbuns]

Is heat-treatment + fret-level a relatively inexpensive way of getting the most of an instrument (long term) that exhibits minor 12th fret kink symptoms. It's a $650 bass.

The kink is more obvious with more relief on the neck. My current specs on a 5er are, 2.5-2mm action (B string-G strings). I can fingerstyle cleanly everywhere, the only issue is popping the D + G string between the 11th-14th fret, there is a buzz. The buzz doesn't go away as relief changes. I'm just trying to get the most out of the bass.

 

[JD Ronson]

I ended up taking my bass in - they started with a a setup, but ended up leveling the frets. I'd stay as far away from heat as possible unless it's EXTREMELY necessary. When all else fails, take it to a REAL pro and get a good assessment.

 

[vaesto]

I've counter-bent the ski-jump on my bass, held it in clamps at +/- 60C for a couple of hours and in the result the jump is gone!!! The real trick is not over bend, since you'll get back-buzz issue, but I was lucky. Now the neck is stright or even has a little fallback past 14 fret. I'll keep an eye on it and check how stable the effect is.

 

[Gigglingbuns]

Is heat-treatment + fret-level a relatively inexpensive way of getting the most of an instrument (long term) that exhibits minor 12th fret kink symptoms. It's a $650 bass.

The kink is more obvious with more relief on the neck. My current specs on a 5er are, 2.5-2mm action (B string-G strings). I can fingerstyle cleanly everywhere, the only issue is popping the D + G string between the 11th-14th fret, there is a buzz. The buzz doesn't go away as relief changes. I'm just trying to get the most out of the bass.

I took my bass to Mike Koontz, a respected luthier Southeast Michigan, he said it just needed a fret-level with the action I was trying to get from it, no ski-ramp/12th fret kink he could measure. So huge sigh of relief.

 

[walterw]

I've counter-bent the ski-jump on my bass, held it in clamps at +/- 60C for a couple of hours and in the result the jump is gone!!!

how did you get that heat and how did you measure it?

 

[vaesto]

how did you get that heat and how did you measure it?

Hi, we've got active ironing board which gives ~80-85 C on the surface So I used it and covered the neck with blanket (several layers), which gave me this temperature on the neck. For measuring I've used cooking thermometer

 

[Fender_Bender]

Interesting thread, one I only found today. I’m thinking a way of making the neck stronger through the critical zone, as well as being able to engineer the strength into specific areas, would be to make a multi laminate neck but with horizontal laminations, not the familiar vertical laminations. You could have a layer of say wenge (or ipe etc) engineered to finish somewhere in the vicinity of the 9-12th fret area with more flexible laminations above it extending the length of the neck to be able to provide the required relief in the lower registers. Could look cool as hell too depending on the species chosen.

 

[Turnaround]

After 3 months I see no deviation. I doubt that I will check and report every month as I originally stated. But I will look again in another 3 months and see if I can detect any deviation. Stay tuned if you have the patience - this is going to take a while.

Last time I checked this test was May. Now in December I have checked again and still no bend in the neck heel.

 

[pigpen1]

Every Fender Jazz I've ever owned, at any price level, had a little ski jump or 12th fret kink. They all have slightly more relief at the 12th fret than at the 7th or 8th. Just a bad design I guess. I'd definitely pause before ever buying another one.

 

[vaesto]

I've heat-treated the neck, which has developed ski-jump about 5 months ago. So now I report: generally the method works, neck is straight again and it looks like it holds the straightness, though, in the first month it has reset a bit, but this might also be seasonal changes. At least I see no obvious ski-jump as it was before.

Here is a picture:

Blue surface is an active (heating) ironing board (kudos to my wife). It heats up to 80-90C. Alternatively any heat source may be used. The only rule - it needs to be consistent and evenly distributed.

Leveler is generic. I've used a piece of band and a screwdriver (clamp is just to hold the screwdriver to tie up the neck at around 12 fret where ski-jump starts so that frets almost touched the leveler. Thick paper under the band and both ends is used just to protect the finish. At the end the neck there is a wooden block between the neck and leveler to make a counter-jump-bend. I've tried to clamp neck to the leveler instead of a bandage, but then it is hard to place the neck on board to transfer the temperature effectively and evenly.

I've covered all this with double layer blanket to keep the temp inside. The neck has got around 60-65C (I've checked the temp at the truss rod nut). I've kept it in heat for 3 hours and finally let it cool down to room temperature for additional 2 hours.

It is a great alternative to the much-surgery re-planing work. It costs nothing (to me) but gives good results. Respect to those guys on youtube and warpedneck.com for sharing the ideas and encouraging me to give it a try.

 

[Gianni "Orlandez" Orlati]

This first thread has been in the works for a while. The "pros" involved in this project are 202dy, walterw, JLS and myself (Turnaround).
I approached the others a while ago after hearing once again that shimming a neck can cause a ski jump. I've heard lots of opinions from many sources about the cause of ski jumps, but no actual facts concerning the subject - opinions are not facts in my book. I decided to enlist a few of my TB friends to join me on a study of ski jumps to uncover the facts about this relatively common occurrence. The result of this effort will show up in this thread.

First, a stab at defining what a ski jump is. It is an apparent rise in the fingerboard and/or neck occurring near the body joint of the instrument and continuing to the bridge end of the neck. This is not to be confused with relief which is a gradual, slight, and relatively even curve along the full length of the board. The ski jump is a much more pronounced curve occurring for a short distance at the butt end of the board. Sometimes this distinction gets lost - I have heard excessive relief called a ski jump - it isn't, it's just excessive relief.

First off, the pro team is going to be examining instruments that exhibit this condition. We are going to MEASURE what is going on. We aren't just going to sight the curves in the neck, we are going to put some tools to work and determine (in thousandths of an inch) just what amount of curvature is occurring, and just as importantly where it is occurring. Important to the study is where that curvature begins to deviate from the normal relief curvature of the neck. Once we have a body of measurements we will be able to start to look for the causes of this deviation.

My thanks to 202dy, walterw and JLS for agreeing to participate in this study. And my thanks to Joshua and Heavy Duty for agreeing to champion this effort and to enlist the support of the TalkBass team.

The day couldn’t start in a better fashion ... very interesting !

 

[Gianni "Orlandez" Orlati]

In my opinion, the ski jump phenomenom could partially be explained using Poisson's ratio, which is the negative of the ratio of transverse to longitudinal strain as a result of an applied stress. After all, a bass neck is essentially a post-tensioned beam-column. In the design of post tensioned concrete, it is necessary to provide stirrups in the post tension anchorage zone to prevent "bursting" in that area.
My background is in structural engineering.

You’re right in using your engineering background in this case but @Turnaround is right .. the ski-jump in a bass neck is just due to the way the truss rod works in relation to the extent of the external constraint provided at the neck heel.
In dealing with beam-like De Saint Venant objects, Poisson’s modulus is not that important and bass’ necks make no exceptions in this regard.
What I still have to see on this thread is how to deal with the issue when in possession of a Fender of Fender-like neck exhibiting ski-jump at various degrees.
I’m not interested in luthier-made instruments, which are made of fancy woods and characterised by questionable shapes, allegedly designed for, inter-alia, minimising the magnitude of any ski-jump occurrences.
I like the feel and how P and J basses sound, and, a combination of the two models made by putting together a P-bass body and a J-neck.
These instruments, however, and especially those provided with a J-neck, seem to be often plagued by this dreaded problem; in my case, if this is case, the neck starts to lift up at the of the neck heel zone and I believe that, aside from trying to adjust the truss-rod, modifying the strings tension trying different types of strings and the like, a nice 0.25 degrees neck shim from Stewmac may help in dealing with the issue, although I still have to try one ...
Any hands-on feedback in thus regard?

 

[_Obra_]

You’re right in using your engineering background in this case but @Turnaround is right .. the ski-jump in a bass neck is just due to the way the truss rod works in relation to the extent of the external constraint provided at the neck heel.
In dealing with beam-like De Saint Venant objects, Poisson’s modulus is not that important and bass’ necks make no exceptions in this regard.
What I still have to see on this thread is how to deal with the issue when in possession of a Fender of Fender-like neck exhibiting ski-jump at various degrees.
I’m not interested in luthier-made instruments, which are made of fancy woods and characterised by questionable shapes, allegedly designed for, inter-alia, minimising the magnitude of any ski-jump occurrences.
I like the feel and how P and J basses sound, and, a combination of the two models made by putting together a P-bass body and a J-neck.
These instruments, however, and especially those provided with a J-neck, seem to be often plagued by this dreaded problem; in my case, if this is case, the neck starts to lift up at the of the neck heel zone and I believe that, aside from trying to adjust the truss-rod, modifying the strings tension trying different types of strings and the like, a nice 0.25 degrees neck shim from Stewmac may help in dealing with the issue, although I still have to try one ...
Any hands-on feedback in thus regard?

I have the same problem on mine 1968 P bass. After reading all this thread I still have a problem with buzz on frets 14 to the last one. Without shim, action is too high, with shim, and truss rod tighten to a maximum, action is better (at Fender specs) but buzzing is still there...It's gonna kill me. I like the instrument so much, it has everything, huge sound, light body, tons of mojo...

 

[Turnaround]

I have the same problem on mine 1968 P bass. After reading all this thread I still have a problem with buzz on frets 14 to the last one. Without shim, action is too high, with shim, and truss rod tighten to a maximum, action is better (at Fender specs) but buzzing is still there...It's gonna kill me. I like the instrument so much, it has everything, huge sound, light body, tons of mojo...

You cannot fix a ski jump with a shim. Some have had success with a heat treatment, some with cutting down the upper frets, and others by re-planing the fretboard. If you try to correct the problem with a shim you are only rotating the problem, but it still exists to the same degree. The kink is still there.

 

[TheLowDown33]

Great thread. As a bass-playing civil engineer/nerd this is amazing content.