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keeping level

Discussion in 'Hardware, Setup & Repair [BG]' started by matty4string, Jun 17, 2016.


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  1. matty4string

    matty4string Supporting Member

    May 11, 2016
    How the hell do i level a fretless neck and still keep the radius? Is it possible if so how? ps i have limited tools
     
  2. sissy kathy

    sissy kathy Back to Bass-ics Gold Supporting Member

    Apr 21, 2014
    Halethorpe, MD
    You don't. Put in a slight amount of bow, then level the string path. When leveling is done you'll have a slight hour glass shape to your fingerboard. @Turnaround can explain this really well, I've called him but you might IM him.
     
  3. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    alpha-music.com
    huh?

    never heard of that method.

    i take out the bow, level by whatever method (same as with frets) then once i've got things perfectly flat (in each string path like you say) relaxing the truss rod a little will re-introduce that slight relief i'm looking for.

    for me it's putting the neck in a tensioning jig to recreate its state with strings on it, then leveling with a long 24" heavy flat beam with sandpaper on it.

    frets or not, it's a matter of sanding evenly across the board so that the radius doesn't get really changed.
     
  4. megafiddle

    megafiddle

    May 25, 2011
    You can preserve the radius (and cylindrical shape) by simply moving the leveling beam continuously from one side of the neck to the other while leveling (sanding lengthwise).

    The slight hump that results from angled strings on a cylindrical neck can be removed by the hourglass shape mentioned above, but if the neck is going to have some relief in it, like 0.010", it's hardly nescessary. The hump only amounts to about 0.001". It would be lost in the relief.

    -
     
  5. Bruce Johnson

    Bruce Johnson Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    The basic answer to your question is that you use a long, flat, hard sanding block, tilting it to follow the radius. Sand with long straight strokes along the length of the fingerboard. Now, sanding with a flat block on a radiused surface means that it is only sanding a narrow little stripe with each stroke. What you do is incrementally tilt the block a little bit with each stroke, working your way across the radiused surface, covering all of it and blending it all into a smooth radius. That's the basic technique.

    You don't need or even want to use a radiused sanding block for this job of truing up a fingerboard surface. You are (hopefully) not taking off very much wood at all, or significantly altering the radius. Radius sanding blocks are more suited for the rough cutting; putting a radius on the top of a new flat board.

    Getting into the finer details of leveling a fingerboard:

    Sissy Kathy has the right idea, but misspoke. What Walter described is correct. Before you start the level sanding, you tighten the truss rod to put a small amount of backbow into the neck. The sanding is done with the truss rod tight. Then, after the surface is level and true, you loosen the truss rod to bring in the amount of relief that you want.

    The hourglass geometry thing is complicated to explain. It becomes more important with smaller radius (rounder) fingerboards, and less important with flatter fingerboards. There's a long, detailed thread about it here on TalkBass from a few years ago. Basically, as you are sanding those long thin stripes down the fingerboard, you need to angle those stripes to match the actual paths that the strings follow. The strings are closer together at the nut than they are at the heel. Sanding the stripe down the center, you go straight down the centerline. As you are sanding off to either side of center, you not only tilt the sanding block to follow the radius, but you also angle the sanding block to follow the taper of the path of the outboard strings.

    The critical thing is that the narrow little stripe of wood directly under each string is straight and flat. Those are what we call the string paths. The wood surface areas between and outboard of the string paths are not as important. They all get blended into a smooth, radiused shape by the incremental tilting and angling of the sanding block.

    I know this all sounds complicated, but it isn't as complicated to do as it is to explain. A correctly leveled and trued fretless fingerboard is more than just a smooth cylinder or even a compound radius cone. To work correctly, it has to be shaped by concentrating on flattening the string paths.

    I usually sand with the long flat hard boards up to 400 grit. Then I use smaller rubber blocks for 800 grit, gray Scotchbrite, and white Scotchbrite to get the scratches out, followed by oil and buffing.

    There's not really many tools needed for truing up a fretless fingerboard. It's mostly patience and technique. And some understanding of the geometry involved.
     
    Last edited: Jun 18, 2016
  6. sissy kathy

    sissy kathy Back to Bass-ics Gold Supporting Member

    Apr 21, 2014
    Halethorpe, MD
    Maybe I wasn't clear, I said 'bow' because forward bow is relief. I thought saying 'bow', rather than the redundant 'backbow' would be understood.
     
  7. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    alpha-music.com
    interesting.

    i've always striven to get it as straight as possible, which often means there might be a slight backbow here and a small upbow there.

    the goal being that they're both about the same distance from the imaginary perfect line, so that i need to remove the least material to get to flat all the way down.
     
    202dy likes this.
  8. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    That's my approach too. String tension will put the desired amount of relief in the neck, the amount controlled by the truss rod. The levelling is done under string tension, or in some cases with simulated string tension, but with the board as flat as possible before levelling begins.
     
    202dy likes this.
  9. Bruce Johnson

    Bruce Johnson Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    To me, the important thing is that the truss ends up moderately tight when the bass is all up to tune with the right relief. That's important for stability, and in many necks, also plays an important part in the sound. So when I surface a fingerboard (or level frets), I first tighten the truss rod fairly tight. Held in that condition, I make the fingerboard/frets flat. When the bass is strung up and pulled up to tune, the neck will usually pull forward into a small amount of relief. It depends on how stiff the neck is. The relief can be fine tuned up or down with the truss rod, but the truss rod is basically tight.

    If you release the truss rod to make the neck flat first, sure, that makes the leveling job easier. But the bass can end up with the truss rod loose when it's tuned up and in playing condition. That's not good. You can't really adjust the relief, and the neck will become much more sensitive to the weather.

    Terminology to me: Bow, Forward Bow, UpBow and Relief all mean forward curvature of the neck; headstock moved forward. Backbow is backwards curvature; headstock moved back.
     
  10. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    alpha-music.com
    well yeah, without a doubt, but that's almost a side issue, whether the neck is behaving properly, meaning that when strung the rod will let you go from too much upbow to actual backbow.

    if you have an issue where you're at one end of the adjustability range, then sure, you can compensate with the leveling to give you more "room" in the desired direction.
     
  11. Bruce Johnson

    Bruce Johnson Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    If you do it right, with the bass up to tune, the truss rod should be at, like, 80% tight with no relief and 50% tight with as much relief as you'd ever want. The rod is partially tight throughout the range. That makes it the easiest to adjust and the most stable.
     
    walterw likes this.
  12. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    Not sure how one would judge when the rod is at 80 or 50%, but agree in principle.
     
  13. 202dy

    202dy Supporting Member

    Sep 26, 2006
    Bruce, just to clarify, using your method the leveling determines where the truss rod nut will be when the fingerboard (neck) is at tension with no relief. Or stated another way, you are adjusting where the zero point for the relief with the neck at tension. If that is correct, do you work with a jig?
     
  14. Bruce Johnson

    Bruce Johnson Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Yeah, that percentage thing is kind of vague. 100% tight is as tight as you dare to go without fear of breaking it. Where that is depends on the design of the truss rod installation and your confidence in the quality.

    The important thing is that you pre-tighten the truss rod enough that you see the neck start moving (in the backbow direction) a little bit. That verifies that the truss rod is working, and that you are in the range where it is working. Hold it there and make the fingerboard straight and true, and you'll know that the truss rod will work correctly when you string it up. Up to tune, you may not have to adjust it at all. The string tension may pull it right into the right amount of relief. But you can go a little tighter or looser as needed, and it will move.

    That's the point of all this. Truss rods only work in a narrow range of tension and movement. You want to set it into the upper end of its range of tension/movement, then make the fingerboard flat.

    On the other hand, don't go too far. Suppose the neck arrives with a significant forward bow. You crank the truss rod up to 100% to flatten the neck as much as you can, then sand the fingerboard level. When you string it up, you find that it's a fairly springy neck, and it still has too much relief. Then what do you do? If you take the truss rod to 110%, you'll snap it. That's why you pre-set the truss rod to 80%, and then level the fingerboard to that neck position. It means that you have to take off more wood during the leveling, but you are correcting the fingerboard to work with the truss rod's range.
     
    Last edited: Jun 19, 2016
  15. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    I'm not sure I would go to those lengths if it were a simple compression truss rod, since it is an easy matter to extend its adjustment range with a washer/collar. But pretty well a necessity for more complex rods where there is no means to adjust their range.