Leveling - techniques for protecting some regions while focusing on others?

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by UsableThought, Jan 7, 2018.


  1. UsableThought

    UsableThought Supporting Member

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    I can show you a graph of exactly what it will look like, and there is no "fallaway at the nut end." I can think of only two ways your statement could be true: (a) if we were to define "nut end" as frets 1-19, which is not a sensible thing to say; or (b) if we lived in a world without adjustable bridges & saddles, which we don't.

    To sum up, sanding frets level from 1-19 with a 0.003" slant down to fret 1 is not going to create "fallaway" at the nut end. Bear in mind how crooked and humped a typical buckled neck is - imagine we simplify it to a 2D profile and draw the whole thing on a graph. Now imagine we pick a straight line that removes the crooks & the humping from this profile, whether we remove the minimum of material or some amount of material more than the minimum. Depending on the exact nature of what is being removed, if we keep the same graph as the frame of reference, the resulting straight line will inevitably have a slant when compared to the horizontal axis. You are never going to be able to draw an "unslanted" line for where your leveling beam will wind up; it will always be constrained by the profile it encounters and how this profile is progressively altered until you get to "done."

    To put it another way, let's say I didn't introduce the tilt at fret 20: I'd now include these frets in the progressively lowering straight line introduced by the leveling beam as I did the work. The resulting line would not be that far off from the line that you say creates "fallaway"; it too would have a "slant" of some sort if you drew the whole thing on a graph. I actually do such graphs as part of my planning; I have a whole system worked out. It's extremely simplified - I follow only 3 lines down the neck, and each line is 2D, so I don't have a 3D plane; but I find it helpful.

    EDIT: Re-reading what you wrote, you're not actually saying anything different than I am. The way you describe it, the 3 low frets at the end of the tongue wouldn't get leveled because they'd be shorter; the way I'm doing it, I guarantee that those frets won't get accidentally touched. But whether we do it my way or your way, the result would look the same if we graphed it - you'd have just as much of a "slant" on frets 1-19 as I would.

    So I think the only disagreement is that we think and work differently and plan for different contingencies; it's not that the work would end up being much different.
     
    Last edited: Jan 9, 2018
  2. walterw

    walterw Gold Supporting Member

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    dude, you've driven off the road, bounced over the ditch and are now tearing through the soybean fields :p

    you're worried about the last few frets? either

    1. the last few frets are in fact lower than the rest, in which case the full-length flat beam won't touch them, or

    2. the last few frets are not lower than the rest, in which case the flat beam should touch them.
     
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  3. UsableThought

    UsableThought Supporting Member

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    So I guess the conversation and technical disagreement has turned ignoring my carefully made points in favor of derogatory language? You made a statement you can't support ("fallaway at the nut") and when I point this out, you don't respond directly, but turn to mockery. I edit my comment to agree that yes, your way could work too; again no direct response from you.

    This isn't like you; you're normally a super guy. Maybe I rub you the wrong way - if so, I'm sorry. Goodbye for now, and hope you have a better tomorrow.
     
    Last edited: Jan 9, 2018
  4. walterw

    walterw Gold Supporting Member

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    i guess it does seem like me and i'm sorry, was not my intent. internet humor translation failure strikes again

    i liked my metaphor about driving into the weeds but it was just meant about the subject at hand, nothing personal at all.

    either way, the correct method for overall tension-leveling with the long beam is without any taping of frets; you adjust the neck for minimal humps and dips and do the whole thing.
     
    Last edited: Jan 9, 2018
  5. UsableThought

    UsableThought Supporting Member

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    Thanks. It may be a small thing, but that makes me feel better. A forum isn't quite the "real world," but I prefer getting along with folks I've come to "know".

    We could get into a whole discussion about jigs which would be interesting in itself. You have far more experience than I do using a jig, not to mention every other aspect of guitars. On the other hand, it's the very fact that I have so little experience that drives me to think harder, question my assumptions, hunt down particular points of interest, and use unusual planning methods a pro simply wouldn't need. No doubt I make extra labor for myself, but I learn more and enjoy it more too. I've made a note of your views and will save it for future reference; so thanks for that also.
     
  6. KGWagner

    KGWagner Member

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    Any tool can be misapplied or improperly used to achieve unexpected or unwanted results. But, I think maybe you're taking the hypotheticals to an extreme here. What you say could/would occur in the situation you describe is true, but it probably shouldn't be a situation you'd try to plow through with a leveling file. If you saw what you're describing, you'd probably want to take other actions first before trying to level the top plane. You're describing an unresolvable (through normal adjustment) bow, which you really wouldn't want to take out with a leveling file. It means the neck geometry itself is a problem, and will almost certainly and ultimately require refretting as you'll need to de-fret it to clear the primary problem, which is a bad foundation. Trying to correct that by leveling the frets will turn the thing into a tar baby where every action you take tends to make the problem worse.
     
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  7. Dave Weir

    Dave Weir Gold Supporting Member

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    At the risk of also driving off into the ditch...
    I was thinking about doing all the final neck carving while it is under final tensions. A couple things maybe you guys have opinions on. is it worth the complications, and could the complications be minimized.
    So if I make the neck as straight as I can, and then bring it up to tension with strings and rod and then get it as straight as I can again, how far off is it going to be? I'm sure every neck is different but are your humps and valleys like .005" or .01" or .25"? Maybe another way to ask is what kind of readings are you getting on those dial indicators?
    And then if you set it all up and level the frets, does the back of the neck still have a s curve? Anything anyone could notice?
    As far minimizing the complications, it seems like there are two forces acting on the neck. The rod trying to make a kind of parabola one way and the strings making an offset parabola the other way and the offset of the two forces is causing the problem. But the strings are really only applying force at the two ends. So if I apply the same forces at the two ends while I shape the neck, and engage the rod, and make it straight, when I string it up it should all be straight, right?
    I have AAA. Should I call a tow truck?
     
  8. KGWagner

    KGWagner Member

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    You may want to watch this video - it may answer your questions.
     
  9. Dave Weir

    Dave Weir Gold Supporting Member

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    Yeah, that's part of it. My construction is a little different but I can build in an up bow by putting some tension on the rod before final shaping, then shape it straight, then relaxing the rod will result in an up bow. .03" seems like a lot, I'm thinking more .01", but I'll give it a try.
    What I was really trying to account for is the little S curve caused by the rod and string pull not having the same apex. I guess another approach would be try to measure where the forces are applied. Jig it up and just apply string tension and measure a bunch of points and then just apply the rod tension and measure the points. I think I'll get two reverse parabolic curves which don't quite line up. Then decide if the offset is not enough to worry about, or can be resolved applying both forces and carve it under tension, or alter the truss rod so the the forces line up better.
    Even though I think I understand the concept, I've never been able to measure this S curve. If I make the neck so it's straight after it's fretted, and then string it up and tighten the rod, they all seem like they are pretty darn straight under tension. So I'm kind of thinking it's not worth worrying about. But if there is a way to realize it and deal with it that's not too much trouble, I always want to do better.
     
  10. KGWagner

    KGWagner Member

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    Not sure why it hasn't been done yet, but a laser might come in handy for some of that. Shoot a straight line, then measure clearance below it. You'd see any unusual or unbalanced curves more easily than you would with a straightedge. But, maybe not. Just a thought I had. Probably seem silly tomorrow.
     
  11. Dave Weir

    Dave Weir Gold Supporting Member

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    So you set up the neck on the jig and get it as straight as you can under tension, and set the dials to zero. Then release the tension and the use the screws and straps to force it back in the same shape. Is that pretty much it?
    Could you do it this way: get it as straight as you can under tension, then leave the truss rod alone. Mark the position of the neck at the nut. Remove the strings, then using only a jack under the nut, put the neck back where it was. Truss rod forces are exactly what they will be in the final set up. A vector of the string force at the nut is pretty close to final set up.
     
  12. KGWagner

    KGWagner Member

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    I'm not sure what you're trying to accomplish. I suspect you're making this much more complicated than it needs to be without any good reason for doing so. But, keep in mind that you'd probably change the geometry of the neck since when strung, it's under more of a shear load than a torsional load. Different kind of stress/tension, and the grain structure/orientation of the wood may affect how it reacts to the different loading.
     
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  13. UsableThought

    UsableThought Supporting Member

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    That is what I used to assume from hearing about the jig, before I actually had the chance to use one myself. StewMac's marketing and instructions seemed to imply that you can trust the gauges as your only guide, and have no worries once you've re-zeroed.

    But as I have since discovered, this simple picture would be true only if you assume the jig itself is so stiff that its frame doesn't deflect that any measurement tool you own could show; and that once you have the dials re-zeroed and the support rods brought up, you no longer have to be concerned about the neck deflecting further - for example, from the weight of whatever tool you're using to level, even if you aren't exerting further downward pressure.

    In my experience, these assumptions aren't true for wooden jigs. Metal jigs I have never used, but metal can't be assumed to be perfectly stiff either - that's why they have elasticity grades for different metals, and probably why StewMac are careful to say only that flex in the metal jig is "reduced," not eliminated. And it's not just me: In my opening post for this thread I linked to a David Collins comment about all this; here is that link again; I very much recommend that persons who are new to using a jig read what he has to say: http://fretsnet.ning.com/forum/topics/are-neck-jigs-necessary?commentId=2177249:Comment:148425

    I especially agree with this point he makes - it describes my own experience to a T:

    "In spite of these weaknesses [the jig] is a fantastic tool, and can be of great use to many. Furthermore, it was a great advancement in the trade compared to average fret work before, not only for aid it may offer in control, but increasing awareness of many factors of influence which were commonly left unconsidered before Dan developed and promoted this tool. This awareness and call to attentiveness may bear more credit for improving the work of many than the tool itself in my opinion."​
     
    Last edited: Jan 10, 2018
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  14. Dave Weir

    Dave Weir Gold Supporting Member

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    What I'm trying to accomplish is little better understanding of the forces acting on the neck, and how I can best accommodate the important ones. I don't have a handle on the difference between the bend created by 100 pounds a couple degrees and half an inch off center and 5 pounds applied at a right angle. I could easily be over thinking it. That's one of my specialities. Along with overlooking the obvious.
     
  15. KGWagner

    KGWagner Member

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    Because we're dealing with wood and its variable density, grain orientation, moisture content, etc., some things are just unknown until the forces are actually applied and we can measure how it reacts. You can expect and predict certain things in general, but mean ol' Mr. Reality dictates that many things be adjustable to compensate not only for personal preference, but for how the parts ultimately behave under stress. Even an OEM like Fender, whose production guitars have a high degree of sameness to them, cannot predict what a neck is going to do even though they're all made of the same material that's cut/shaped on super-accurate CNC machines. You can read many stories from many sources over many years how some players will sit down at the dealer and go through 10-12 "identical" Strats and only like the sound/feel of one (if any) of them.
     
    Last edited: Jan 10, 2018
  16. Dave Weir

    Dave Weir Gold Supporting Member

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    I get all that. So let's back up. What is the point of the neck jig contraption? If it's to simulate the effects of string and rod stress when you level the frets, is there any advantage to simulate those stresses while carving the neck?
     
  17. KGWagner

    KGWagner Member

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    I can't think of any, but I'm not the last word on such things, either <grin>

    Besides, assuming you were able to stress the thing accurately before carving, the very act of carving it would change how it behaves. Cross-sectional geometry would change as you cut away material, which would change its longitudinal strength/stiffness, allowing grain pattern pathways to exert more or less influence on or resistance to stress. Then, you have to fret the thing, which adds a LOT of stress that's not even in the wood to start with. So much so, you sometimes don't even have to measure it - you can see it. I'm sure there are other considerations, but just those two alone are huge and should suffice to stop any further travel down that path.
     
  18. Jack Daniels

    Jack Daniels Supporting Member

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    I have built hundreds (really) of necks that are in use around the world today. I can't see an advantage of carving the neck while in a jig simulating neck tension. But I do build with the end in mind.
     
  19. Dave Weir

    Dave Weir Gold Supporting Member

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    I have a pretty good idea how fretting affects the woods I use. I can deal with that. I'm only using two kinds of frets and one saw. It seems like refrets to a customer specs would be a lot more difficult.
    And I was also thinking that it would all change as I cut it, so that was really the point of the first questions. How much "error" would I want to accommodate? Maybe carve the neck unstressed say to within .05" and then apply the tensions. You guys are probably right. More trouble than it's worth.
    To Usable Thought: Sorry I kind of went off topic. You have a lot of people I really respect looking at this thread and I kind of wanted to get involved. Then you go quoting David Collins and I'm hooked.
     
    Last edited: Jan 10, 2018
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  20. Jack Daniels

    Jack Daniels Supporting Member

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    Fender built 10's of thousands of necks without any kind of special tension jig. They work ok.
     

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