Getting the Facts about Ski Jumps

[_Obra_]

I am glad to see that this topic is still not neglected, although it means that from time to time, unfortunately, someone with the same problem appears.

Since I bought my P bass from 1968 exactly a year ago, I have a dilemma whether to fix the small ski jump or to leave it as it is and thus not reduce the value of the bass.

Since in my case the ski jump is relatively small, and the only problem it creates for me is a small buzz from 15 fret to the end of the neck, it is very possible that the solution is to just replace and level the frets.

The Rosewood fingerboard is very thin especially in the lower part of the neck, so I would not try to solve the problem by leveling the layer of fingerboard wood or any other radical interventions on the wood.

My question is whether replacing the frets on the original instrument would reduce its value during a potential sale, or is it better to try the third option, and that is straightening wood with pressing and heating?

 

[Pilgrim]

I'm following this thread because I have a 1963 P with a 1972 neck on it. The neck has a slight ski jump which doesn't really get in my way, as I don't play much above the 5th fret. However, it would be nice to correct the issue.

 

[Turnaround]

So in your experience can you tell us if the wood in most necks eventually achieve a point of stability after being compressed by string pressure? Or does the ski jump effect typically continue to worsen over time? Or is it a case by case basis that is dependent on the wood of each neck? Are some types of wood less prone to incurring a ski jump?

I'm sure there must be a limit to the amount the neck will bend. I don't know what it is, but I think that a ski jump will likely continue to get worse over time. It's not like "fret sprout" where the fretboard shrinks across its width in drier conditions, then expands again when there is more humidity in the air. A ski jump is not caused by changes in humidity, it is a result of constant strong bending forces. The forces do not reverse over time so the bend never gets an opportunity to straighten out. It would be nice if you could just remove the tension and the neck would move back over time of its own accord, but unfortunately that doesn't happen.

Some necks never develop a ski jump. And that has to do with two major factors. The first and most important is the rigidity of the wood. Slow growth wood tends to be more rigid than that which has grown quickly. So as a maker you would favour a piece of wood with close growth rings over one which has wider rings. But rate of growth is not the only factor, and it is not really possible to tell just by looking at a piece of wood. So yes, the propensity for the development of a ski jump is dependent on the particular piece of wood and the forces acting on it.

Looking at the problem from a different angle, the more tension there is on a neck, the more chance there is that it will kink near the 12th fret. So high-tension strings are more likely to induce a kink than low tension strings. You might think too that a 5 string bass might be more prone to the condition than a 4 string, but the additional amount of wood in the 5 string neck offsets to some degree the tension induced by the additional string. So it may not be more or less prone to kinking.

I don't have enough data to form conclusions about which species of wood are better or worse at resisting ski jumps. Perhaps some of the other pro's in this forum have data. I'll wait for them to chime in.

In the next post I will talk about a number of ways to deal with a ski jump - from least to most intrusive. And I will have a look at the effectiveness of different methods.

 

[Turnaround]

How to Treat a Ski Jump - Part 1

If you have been following this thread, you will know what a ski jump is and how it is formed. Here I will outline methods for treating the ski jump/12th fret kink, starting with the least intrusive and proceeding through progressively more intrusive procedures.

1. The first approach may provide a very satisfactory result for a mild ski jump. Live with it. You can live with it as is and just not play up on the higher frets. But by modifying your setup procedure you may be able to arrive at a setup that doesn't buzz yet maintains pretty low action.
Normally when doing a setup the relief is set first, then the saddle heights are adjusted. But to optimize the setup where there is a ski jump condition it is often useful to reverse the order and start with the bridge saddles. The reason is that the truss rod has little to no effect on the area of a neck between about the 12th fret and the butt end. And that is the area where the ski jump occurs. So we first concentrate on getting the bridge adjusted so that the bass plays well from the 12th to last fret, then deal with the neck relief.
I know there will be those that say "but neck relief will affect string height so we should set relief first then adjust the bridge for overall action". Well, we're talking about trying to arrive at a compromise position here, one that deals with a non-level fretboard, so we are approaching the whole setup differently. Some illustrations will help.

In the diagram above, the black line represents the neck with a kink (highly exaggerated) at the 12th fret (arrow). The red line is the string, and the triangle is a bridge saddle. Looking at the 12th fret, the action seems high. Measuring the relief by fretting the first fret and where the neck meets the body and checking the gap at the 7th fret (arrow in illustration below) indicates that the relief is decent (actually it isn't, but the measurements seem to indicate that it is).

But you can see that the string will be laying right on the frets when we play anything from the 12th fret up.

Since the truss rod won't help us in the area beyond the 12th fret, we need to address the choking on the upper frets by raising the saddle. Once you have the saddle set to play cleanly beyond the 12th fret leave it there. No matter what you do with the rest of the setup the saddle must be there to avoid fret buzz beyond the 12th fret.
Now you can deal with the neck relief. If you change the amount of relief you will be affecting the open string clearance on the entire neck, but it will not affect the string clearance on fretted notes from the 12th fret up. By its very nature neck relief will affect fretted string clearance mostly in the first 3 to 4 frets with diminishing effect as you move up the neck. So concentrate on getting the relief set right so that the neck plays cleanly on frets 1 to 4. You may well find that the amount of relief is less than you normally have.
This is a compromised setup, but if the ski jump is mild you may well find that it's entirely workable and not much of a compromise at all.
In the next post I will deal with something that is often suggested as a way to deal with a ski jump, but is actually not effective. And in further posts I will discuss more intrusive measures.

 

[Whale]

Watching this thread with rapt attention!!

 

[_Obra_]

Watching this thread with rapt attention!!

Best thread on TB

 

[JuanB]

A big thanks to the pros contributing to this thread. I was curious if basses where the truss rod adjustment is at the heel of the neck are less prone to ski jumps forming. I figured if the truss rod is making it all the way to the heel, there would be some greater structural rigidity at the transition from the neck to the body. In particular, I was wondering about basses similar to Stingrays which have a truss rod wheel just outside the heel of the neck.

 

[Turnaround]

The location of the truss rod adjustment has little bearing on the propensity of the neck to form a ski jump. Any effect the truss rod will have will be minimal. Bruce Johnson has done lots of work in the area of rigidity and re-inforcement to counter the stretching that results in a ski jump. Check out posts around #99 in this thread.

 

[Whale]

Turnaround, I imagine you will be discussing fretboard leveling in your upcoming entry regarding "more intrusive measures". I was wondering if you might provide some insight into leveling the fretboard without string tension and how the leveled neck then reacts once the strings are reinstalled. When pressure is applied again does the ski jump typically reappear, but to a lesser extent or ???

 

[Turnaround]

Turnaround, I imagine you will be discussing fretboard leveling in your upcoming entry regarding "more intrusive measures". I was wondering if you might provide some insight into leveling the fretboard without string tension and how the leveled neck then reacts once the strings are reinstalled. When pressure is applied again does the ski jump typically reappear, but to a lesser extent or ???

I’ll be sure to address your question.

 

[Gilmourisgod]

I sense clarity emerging from my mental fog on this subject, gonna try the "live with it" approach on my ski-jumped MIM P bass ASAP. Looking forward to more, which im guessing involves some fret filing.

 

[Turnaround]

This time I’m going to look at something that is somteimes suggested as a way to handle a ski jump, but is not actually effective - a shim.

The suggestion of using a shim in such a case comes from a misunderstanding of the geometry involved. The thinking is that since the ski jump is a rise at the butt end of the neck and by using a shim to tilt the neck forward you can alleviate the ski jump.

You often see a ski jump depicted like this (exaggerated):

The butt end of the neck is no longer parallel to the plane of the body. So if you were to add a shim on the outer end of the neck pocket you could bring the upper end of the neck parallel to the body again.

But it's not really like that at all. If we make the body of the bass transparent we can see that the neck in this illustration is not seated in the pocket.

Of course this isn't what's happening - the ski jump condition does not lift the tail end of the neck up from the base of the pocket - it's screwed down there. So the geometry of ski jump is not that the tail of the neck has lifted, it's the headstock end that has raised with the bending point being near the 12th fret.

The problem here is that if you lower the bridge saddle enough to get decent action at the 12th fret, it will choke out as you fret further up the neck:

So if you were to treat the ski jump with a shim in the outer part of the pocket you would just end up raising the headstock end even further. And as a consequence the action at the 12th fret will be higher. If you now lower the bridge to achieve the previous string height at the 12th fret you end up with the same geometry as you started with, just rotated slightly. The relationship of the strings to the neck remains the same and your ski jump problem remains.

With the shim in place we could try to make it work by first raising the saddle so that it plays cleanly past the 12th fret, but of course that would raise the action higher. And it's a mistake to try to further compensate by adjusting the truss rod - there's no relief in the neck now - just a kink, and right where you don't want it. Relief is meant to give added clearance at the first few frets, not around the 12th. Using the truss rod to compensate at this point will add a backbow into the equation and we end up with what some call the dreaded S curve.

All of these illustrations are of course gross exaggerations. But they do illustrate what is going on and why a shim treatment is the wrong approach since it ignores the fundamental nature of the ski jump. An effective treatment will deal properly with the geometry. So in the next post I will start to look at the ways we can correct that geometry.

 

[Turnaround]

How to Treat a Ski Jump - Part 3

OK now on to effective treatments. He's what I will be discussing, from least to most intrusive:

1. Reversing the kink
2. Levelling the frets
3. Levelling the fretboard

But before I go further I should mention that though I am using a fretted instrument in these examples, ski jumps also happen in fretless instruments. The principles are the same and I am not going to insult your intelligence by going over how anything I say relates to fretless. You can figure that out.

The first and least intrusive way of dealing with the ski jump is to reverse the kink, typically by heating the wood and bending it back. Why, you may ask, do I consider this the least intrusive when you could treat it in what may be an easier way? Because the other ways involve cutting some bits away, either filing down the frets, or planing down the fretboard. Heat treating takes nothing away (assuming you can do it without damaging the finish) so it is the least intrusive.

WarpedNeck.com is worth checking out as a place to have this heat treatment done if you are not able to do it yourself. The method involves heating the neck in the area of the kink, bending it back and clamping it there (or slightly over-bowed) and letting it cool.

I don't use this treatment because I am not convinced that it works. It may seem to work for a while but too often I have seen heat treated bends revert to their bent state after a period of time. However, I have heard of many heat treatments that seem to be holding after a longer period. And actually an induced bend like a ski jump is more likely to respond well to heat treatment than other kinds of warps. The reason is that many warps are not a consequence of the wood being stressed after it was fabricated into a neck, they are the consequence of natural stresses that occurred during the growth process of wood. If you had a board that was cut from a tree that was growing on a slant, there is inbuilt stress in the wood that helps to counteract the effect of gravity on the leaning tree. When that tree is cut into boards, the boards will start out straight but as time passes the wood will adapt to the lack of angular stress and the internal structure will flex the board into a relaxed state, i.e. warp, evening out the internal stresses. In the case of a ski jump, the wood started out relaxed and was stressed under string tension until it bent and gradually it held that bent position. Theoretically heat treating will allow the internal induced stresses to relax and the neck will settle back into its original state. Still I don't go that route - it's effective, maybe. I'll go into this further later on.

The second treatment is, as so many have suggested, fret levelling. Here's the crux of it. We know the ski jump is a kink in the neck above the 12th fret, so it seems logical to treat the neck. But actually we don't need to worry about what the neck is doing so long as the frets are on the same plane. For that matter the neck could have all kinds of hills and dales, but if the fret tops are even it will play great. So forget about the neck, let's just treat the frets. If the frets are large enough we can just level them and we're good to go. Here's an illustration of a fretboard with a ski jump - the kink occurs just past the 12th fret (the 12th fret is in red).

You can see that as it stands a straightedge along the upper frets shows that there is a gap that is apparently largest at the 15th fret. And here's a straightedge that continues the straight line along the fret tops on the rest of the neck to the 12th fret:

So clearly if we cut down the upper frets we can put all the fret tops in the same plane. But as you can see, the last two frets are going to get cut down a lot leaving very little fret left. In this case I would suggest that the ski jump is too severe to use the fret levelling method as an effective treatment. If the ski jump was milder, fret levelling would be a good choice. So how can you tell if your bass is a good candidate for fret levelling? A straightedge is going to show you a gap, but it doesn't directly tell you how much you would have tp remove from the upper frets. It does tell you indirectly. In the upper illustration you can see that the gap is largest half way between the ends of the straightedge, i.e. at the 15-16th fret. Since that gap is halfway between the endpoints, the gap in the middle is half of the amount that will need to be removed from the last fret. If you use a feeler gauge to measure the gap at the 16th fret, double that amount. Measure the height of the last fret. Subtract the fist measurement from the last and you have the finish height of the last fret. Take a look at a feeler gauge that is that calculated amount - that's going to be the height of the last fret. Remember that when you cut the frets down you will need to re-crown them so there has to be enough fret height left to accomplish that. It gets increasingly difficult as the fret height lowers.

So if fret levelling is going to leave the last fret too low, we will need to lower the fretboard rather than the frets. This involves removing the upper frets and planing the fretboard flat, then replacing the frets and levelling them. However we can run into cases where the ski jump is so severe that planing the fretboard will reduce its thickness to near zero or worse:

The red line shows the cut line, leaving very little fretboard thickness at the butt end. If the fretboard were thin to start with this cut would go completely trough it. In a case like this it may be worth considering a combination of a partial fretboard planing with a fret levelling as above, i.e. cut down the fretboard a bit, and cut down the frets a bit. And of course you can use a variation of the technique I outlined above to pre-determine how much of the fretboard you will need to cut.

But now the caveat.... every "effective" treatment I have outlined may only be temporary! No neck is manufactured with a ski jump - it develops over time as a consequence of the stress put on the neck by string tension. If the neck bent under the strain, there is no reason to assume it won't bend more. At one point the neck was straight. Let's say it developed a severe ski jump after ten years. If you had treated it at the 5th year you would have had another mild ski jump at the ten year mark. The problem is that there is no way to know. Is it done bending? And if I straighten the neck with a heat treatment or modify the frets or fretboard, why should I expect the neck to better withstand the bending stresses when I apply string tension? It bent once - it is likely it will bend again.

If necks are susceptible to the development of ski jumps, isn't there something that can be done to prevent them? Of course. Bruce Johnson has addressed that in this thread around post #99. But that adds cost to the instrument and in a highly competitive environment manufacturers have to weigh additional costs and the effect of higher pricing on their ability to capture and hold market share. So strapping the neck as Bruce suggests is rarely done. But perhaps it is advisable to apply re-inforcement as part of treating a ski jump.

Some specific questions have been raised in this thread and I intend to address them in the next post or two.

Thanks to all who have provided comments on this thread. It's encouraging to get feedback.

 

[Turnaround]

Turnaround, I imagine you will be discussing fretboard leveling in your upcoming entry regarding "more intrusive measures". I was wondering if you might provide some insight into leveling the fretboard without string tension and how the leveled neck then reacts once the strings are reinstalled. When pressure is applied again does the ski jump typically reappear, but to a lesser extent or ???

As mentioned in my last post, I intend to answer specific questions that have been raised. And this is one.

A ski jump is caused by the tension of the strings. Typically it takes some time to develop, and it becomes "set" - i.e. when string tension is removed it is still there. If you level the frets or the fretboard it doesn't immediately form a ski jump when the string tension is reapplied.

But your question brings up another item of interest - that of levelling without string tension. With a decent quality neck you can reasonably count on a satisfactory result when levelling when a neck which is not under string tension. You start by getting the neck as straight as possible, then level the frets. Then when the neck is installed it will bow under string tension which you control with the truss rod to give the desired amount of relief.

BUT - there are three gotchas when using this approach. When I say "start by getting the neck as straight as possible" you would do that by tweaking the truss rod. Under ideal conditions you won't need any tension on the truss rod at all to get the neck flat (that's the was it was manufactured). But if it takes a little tension on the rod it's probably OK. But if it takes a fair bit of tension on the truss rod to get the neck flat you are starting with a significantly compromised neck and the results will likely be similarly compromised - perhaps very seriously.

The second gotcha bass to do with the quality of the neck wood. An ideal neck is stiff and resists bending. There are a few brands of mass-produced instruments that seem to use far less than ideal wood and you cannot count on them behaving at all well under string tension. This lack of quality is usually reflected in their price. Not always though.

The third thing has to do with how a specific neck behaves under string tension. Ideally the neck would bow evenly giving just the right amount of relief. But wood in not a homogenous material, and it does not always bend in a nice even curve. So if we level a neck without string tension, there is no guarantee that it will form a nice even curve when under tension. One of the ways to deal with that is to put the neck under tension when it is levelled. There are tensioning jigs that will do that. They are not a perfect solution, because you put the neck under simulated string tension, then get it as straight as possible, then level the frets. Hopefully the neck under tension will form just the right curve when the strings are re-installed and the trussrod relaxed a hair to induce relief. It's a pretty good bet that it will be near ideal, but it is possible that the relaxed trussrod will induce an uneven curve - actually highly unlikely.

A variation on using a neck tensioning jig is to level the frets under real string tension. You leave the strings on the instrument, tuned up, and use a special beam that rides under the strings. You need to raise the strings up a bit at the nut to provide clearance, but this method works well.

I hope this answers the question.

 

[Bruce Johnson]

If you want to know more about pre-tensioning necks while leveling, here's an old thread where we went into the subject in great detail:

Stewmac/Matt Vinson Style Neck Jig

This thread also covers the same subject:

Neck jig for fret level?

 

[Whale]

Thanks to both Turnaround and Bruce for the VERY helpful information!! Your experience and patience is more appreciated than either of you might realize. The hours you've put into researching the issue(s) and the hours spent sharing your wisdom help bassists across the globe.

The reason I've been following this thread is due to a "ski jump" neck on a vintage bass that is not only valuable, but is very special to me. Previously, someone tried to level the frets, but (as you might suspect) the last few were taken down to almost nothing and there is still a fair buzz happening. My fretboard is not a thick slab of rosewood. Fender constructed my specific model with an ultra thin fretboard so planing it level is not an option. Even if I set up a jig to mimic the effects of string tension a few swipes of the plane would remove the fretboard completely.

I suppose that I could add a new neck and toss the original off into the corner, but I like the feel of the original and if at all possible I'd prefer to keep my bass "intact". A "perfect" replacement neck from the same year would be nearly impossible to find, too.

With very few options left available to me I haven't much choice but to roll the dice and see if Erik at WarpedNeck.com can work his magic for me. I will, of course, have to refret my neck, as well. I will be sending my neck to Erik shortly. Fingers crossed, but whatever happens I will definitely report back on the results.

 

[Bruce Johnson]

Thanks to both Turnaround and Bruce for the VERY helpful information!! Your experience and patience is more appreciated than either of you might realize. The hours you've put into researching the issue(s) and the hours spent sharing your wisdom help bassists across the globe.

The reason I've been following this thread is due to a "ski jump" neck on a vintage bass that is not only valuable, but is very special to me. Previously, someone tried to level the frets, but (as you might suspect) the last few were taken down to almost nothing and there is still a fair buzz happening. My fretboard is not a thick slab of rosewood. Fender constructed my specific model with an ultra thin fretboard so planing it level is not an option. Even if I set up a jig to mimic the effects of string tension a few swipes of the plane would remove the fretboard completely.

I suppose that I could add a new neck and toss the original off into the corner, but I like the feel of the original and if at all possible I'd prefer to keep my bass "intact". A "perfect" replacement neck from the same year would be nearly impossible to find, too.

With very few options left available to me I haven't much choice but to roll the dice and see if Erik at WarpedNeck.com can work his magic for me. I will, of course, have to refret my neck, as well. I will be sending my neck to Erik shortly. Fingers crossed, but whatever happens I will definitely report back on the results.

If you want to permanently repair and save this neck, keeping it as original as possible, here's what I would do:

First, use the heat method to get it as close to straight as you can. WarpedNeck.com are very good at that. Second, add the carbon fiber backstrap under the skunk stripe. I went over this some pages back on this thread. This will guarantee that it won't pull back, and is a nearly invisible repair. After those things are done, pull the frets, lightly resurface the fingerboard, and refret it.

 

[Whale]

If you want to permanently repair and save this neck, keeping it as original as possible, here's what I would do:

First, use the heat method to get it as close to straight as you can. WarpedNeck.com are very good at that. Second, add the carbon fiber backstrap under the skunk stripe. I went over this some pages back on this thread. This will guarantee that it won't pull back, and is a nearly invisible repair. After those things are done, pull the frets, lightly resurface the fingerboard, and refret it.

Thanks for the advice Bruce. Sadly, my neck doesn't have a skunk stripe. It's a 1982 Fender '62 AVRI, so the only way to add a carbon fiber insert is to pull the fretboard and route a pair of channels beside the truss rod... which I'm not opposed to doing. But since that is a fairly involved task I'll do as you suggest by trying Erik at WarpedNeck first to see how well he does with my neck.

 

[Turnaround]

My question is whether replacing the frets on the original instrument would reduce its value during a potential sale, or is it better to try the third option, and that is straightening wood with pressing and heating?

Opinions vary about whether or not fret replacements lower the value of a vintage instrument. If a potential buyer is a collector of vintage instruments that does not intend to play it, just display it, then original worn frets may be of value. But if the buyer is a player I would say replaced frets add to the value if they were replaced well and with the appropriate wire. Consider frets to be like tires on your car - they are consumables - they wear out and you replace them. So replacing them as part of other maintenance is also valid and does not reduce the value of the instrument.

At least that's my take on it.

 

[_Obra_]

Opinions vary about whether or not fret replacements lower the value of a vintage instrument. If a potential buyer is a collector of vintage instruments that does not intend to play it, just display it, then original worn frets may be of value. But if the buyer is a player I would say replaced frets add to the value if they were replaced well and with the appropriate wire. Consider frets to be like tires on your car - they are consumables - they wear out and you replace them. So replacing them as part of other maintenance is also valid and does not reduce the value of the instrument.

At least that's my take on it.

Thanks so much for Your appreciated opinion