Even fretless fingerboard levelling tips

Discussion in 'Luthier's Corner' started by jesterbass, Aug 6, 2012.

  1. pilotjones


    Nov 8, 2001
    Right, sort of - with a minimal wood removal application, it should remove nothing along the centerline; and along the edges, you should loose a little in the middle of the length of the fretboard but nothing at the nut and body ends. Right, HJC?
  2. suraj


    Oct 1, 2008
    Mumbai, India
    Sounds perfect..and exactly what i thought..although the absolute least wood removal would be to just use the radiused sanding block, just so the OP can level the CA bumps WRT the fretboard. with no wood removal, theoretically. However it is his choice if he wants better action and a conical board and should then listen to musiclogic..
  3. jesterbass


    Apr 20, 2007
    It's nice to see you guys discuss "advanced" procedures like conical sanding that I had no clue existed. Thanks to all the pointers and especially to Son of Magni for the following, I saw the light after this. :)

    Before jumping to conical sanding though, back to the problem at hand. A little more info about the neck:

    - 4 piece maple neck/wenge board
    - 5 strings, 32" scale, no problems at all when it had frets (not so sure this will be the case after I 'm done with it though)
    - radius: Specs say 26". However, my 20" sanding block matches perfectly with the nut side, so I am assuming a compound radius since the bridge side indeed seems much flatter. The luthier that took a glimpse of it had reported the same, 20" nut, 26" bridge. I do not believe the difference is there because of hand sanding as it was very slight.
    - The rod is indeed dual action. With neck off the bass and the rod completely loosened in the middle/dead zone the neck naturally has a slight forward bow. Using truss rod pull, it can go very flat (again talking off the bass). I 've never had to use truss rod push with this neck, since it bows forward naturally and the strings obviously increase that bow.
    - Fingerboard thickness is 4.5mm at the nut and bridge edges, and a little less in the middle of the board, about 3.5mm

    Although I suspect you guys found it interesting as a challenge in repair jobs you might be doing and such, my obsession with minimal wood removal is not lack of fingerboard thickness (although that might be a problem down the road when I will have eaten most of it still being unsatisfied). I was hoping to only slightly modify the factory levelling. Somebody mentioned fretted necks have much more relief than fretless out of the factory, so I am guessing I should forget that rationale. Most importantly, more than a little sanding will have to be done to get rid of the CA "frets". Here's a nice pic I just took for you, I used the light under the ruler tip I read on this nice thread. :)


    Now, the way I see it I have the two following options (after which I should do a bit of conical sanding):

    a) Only use a long beam to remove the CA "frets", keep most of the original radius work.
    b) Use the 20" radius block (8" long) to recreate a single radius then take it from there.

    Hand sanding has made my board flatter at centerline and I don't like the looks of that, so I think I am going for the second option. The big issue right now (applicable in both courses of action I think) is how do I sand, and more specifically the truss rod. Someone suggested a loosened truss rod but that would have me sanding on a neck with relief. Do I sand with truss rod pull so that the neck is as flat as possible instead?

    Come to think of it I have two problems instead of one, losing the CA frets plus flattening the board.
  4. suraj


    Oct 1, 2008
    Mumbai, India
    Now thats enough info to get proper advice :) To me, the larger light gap between your frets there is either because of the way you sanded it (doubtful, as it would have happened on other fret spaces too), or wear and tear from the strings with usage. It seems to me that its not the CA bumps that are causing the "light" everywhere.

    Either way, you will need to proceed with leveling the entire board. WRT the truss rod, yes, if your neck already has some natural relief to it after loosening the truss rod, then by all means use the truss rod and get the neck as straight as possible. This will ensure minimal wood removal. The next thing is that I would support the neck from the underside to minimize flexing with your sanding pressure. You may not have a neck support caul thingy, but you could use say a bag of sand under the neck so it conforms to the shape a bit and still gives some support. or use shims.

    Then get yourself a white pencil and draw lines all over your board. When you sand (with the sandpaper attached to the beam), the points where the sand paper will contact the board will be the high spots. So you will be removing the high spots along with the white pencil marks on it, leaving yourself with areas that have low spots and the pencil lines intact. Sand with the string direction till all the pencil marks are gone. Use the ruler constantly to check for light. Again check with the ruler only in the direction of the strings. Its not very easy to sand with the string paths perfectly so go slow. And go in one direction, don't go back and forth as you won'y have enough control and you don't need to remove too much material. Use good quality sandpaper for faster cutting action. I would use 100 grit for this step.

    When your done, you might find that the edges of the fretboard now have a bit of a sharp edge. For that you could just use 400 grit paper, using your finger as a backing, and sand the edge along the length at a 45degree-ish angle. This will give a mild roundness to the edge and will increase comfort. This procedure however is optional.

    Since you claim you may have flattened the curve of the board in places, after your done leveling, hold a long piece of sandpaper, draw white lines all over the board again,
    and sand similar to this -

    Although he is sanding the neck, you will do to the fretboard. And the slight modification in the sanding action you will have to make would be to go more side to side than up to down. Think of a clock, the guy in the video is sanding with his right hand going in a 5:30 direction and left hand is going 6:30.

    You will have to do about 3:30 and 8:30, as the fretboard is not as round as the neck.

    Be careful with this step, it is not necessary if you did a good leveling job and sanded the radius lengthwise with the beam instead. This step should be carried out only with a high grit paper to remove just the straight ridges left by the sanding beam. An alternative to this would be using a softer, say rubber, sanding block length wise like the beam.

    Lastly you may have to deepen your nut slots for better action and lower your bridge saddles a tad if need be.

    well thats it, i guess. I would not use the radius sanding block on a compound radius board. if you really want to, you may have to remove the nut and sand ONLY on the nut side. If you sanded the whole board with the radius block, you would remove about 1mm thickness, or a little less, from the edges of the fingerboard higher up the neck. then using the beam you will have to consistently remove 1mm from the nut side and level..!! thats too much wood removed.

    Hope this helps, and hope I made sense. And anyone please correct me if I have said something wrong.
    Rolling Thunder likes this.
  5. Meatrus


    Apr 5, 2009
    Sorry to go back to this instead of giving advice. But I have had a question in my head about this for like a year now after reading this http://liutaiomottola.com/construction/FretDressing.htm, its about halfway down the page on the fret leveling section.

    In brief, he said that on a fretted insturment if you level your frets flat with a file, instead of with a radius, there is no point in a conical fingerboard. As the shape of the fretboard underneath the frets is unimportant to a point, because your playing on the flat surface of the frets. Just as if you had a flat (sorry infinite radius :)) fingerboard to start with, which does not suffer from the problems a cylinder would. He made the point better than me....if what I said didnt make sense check out the link. The article made sense to me, but I'm guessing there might be more to it?

    Edit: Copied the paragraph (should have just done that in the first place): To obtain low action some luthiers use what is called a compound radius fretboard. Fretboards of this type have their playing surface shaped like a section of a cone. But the work involved in making such a board is completely unnecessary, as optimally low action can be obtained by simply dressing the frets in a normal fashion. There are two reasons for this. The first is simply that the shape of the fingerboard surface is of no consequence when it comes to low action - it is the shape of the surface described by the fret tops that matters. The second reason is that the difference between an optimal fret top surface shape and a purely cylindrical shape is so small that you will generate the optimal shape automatically, as a consequence of normal fret dressing. Here's why.
  6. suraj


    Oct 1, 2008
    Mumbai, India
    As I understand it, this is completely true, BUT if you level the frets to form a conical surface while they are installed on a cylindrical board, you will be removing significantly more material from some frets than others. specially on the middle frets towards the edges of the board. The first and last frets will be untouched, while the edges of the middle frets will go down in crown height by about 0.5mm on say a 16" radius board. on a 12" radius board the crown height may go down by about 0.8mm on the middle fret edges!! For small fret wire that much material will almost remove the fret..!! I feel it is better to make a board conical and let the frets conform to exactly that shape. So when you level the frets, you will only scrape the top surface followed by a re-crown. If your board has a 16" or greater radius, I feel, making the fret tops conical is not a bad option.
  7. Musiclogic

    Musiclogic Commercial User

    Aug 6, 2005
    Southwest Michigan
    Owner/Builder: HJC Customs USA, The Cool Lute, C G O
    This is where this has gone completely awry, and why I stopped commenting.

    People making assumptions about what is being said instead of just reading what is stated.

    Conical leveling with the string paths is not creating a compound radius, that was an assumption put forth because so few understand the purpose of conical leveling. The OP was asking about doing his fretless, and this keeps getting turned into a "Fretting" hijack.

    Conical leveling creates a smooth transition along the string pathways, this is the idea. NOT CREATING A COMPOUND RADIUS!!!!

    THE OP has been using a radius block to level his fingerboard, NOT FRETS, FINGERBOARD.:rolleyes:

    If you read further in the article posted above, the author clearly explains that leveling with a block would take "Special Effort" to create the natural string paths that are done when an experienced luthier levels with a long file. Thus why you level with a file, and why when leveling with a file(Or long aluminum or stone block) you follow the taper of the board unlike the cylinder path made by the radiusing block.

    We are trying to set an inexperienced hobbiest along the correct path to success, and this has been turned into a complete clusterf#@k, because nobody can stay on the point of the OP trying to get the best surface for his fretless conversion.:meh::rollno::scowl:

    Sorry, I just get frustrated when people here do this to so many threads
  8. Meatrus


    Apr 5, 2009
    Wow, just when I was starting to like you :eyebrow::). I'm well aware the OP is talking fretless. But if you read the part where I quoted you, you will see that you brought in fretted instruments first. So I didnt think it was too much of a stretch to mention them again with a simple question, especially as the OP has already said that he is enjoying learning from the off topic stuff. Seeing as the OP isnt botherd, why should you be? If he is, why not leave that up to him to say, instead of deciding what can be talked about in other peoples threads.

    I suppose I should end with a redundant sorry too ;).

    Edit: Suraj, I believe the actual amounts to be removed are in the article.
  9. jesterbass


    Apr 20, 2007
    Woah, can I decide what's being said on my thread? Then I 'd rather we stayed on topic. :-D
  10. Big B.

    Big B.

    Dec 31, 2007
    Austin, TX
    OP, you'd be smart to listen to what musiclogic is telling you. We've had private conversations about fretting and radiusing (among other things) and I can tell you he's as knowledgeable as anyone on this forum and has the resume to back up what he's saying. (Of course its up to you to decide what my opinion is worth) ;)

    Whether you accomplish it by using a flat or radiused board straight string paths are the goal.
  11. suraj


    Oct 1, 2008
    Mumbai, India
    Thanks for the link, that was a great article. I also made a drawing and realized I was wrong :bag: I also realized that leveling with string paths on a single radius board doesn't mean it gets converted to compound radius. Which means Musiclogic was right all along. Which also means we stole this thread :p

    Sorry OP :)
  12. 49sfine


    Apr 20, 2008
    Austin, Texas
    Interesting dialog and I learned some stuff too - kool. I just keep thinking that the opportunity to make a lined fretless with actual wood inlays was missed in lieu of CA glue. If it were mine, I would have glued in small strips of an appropriately colored wood and avoided the whole CA glue sanding fiasco. Still, it was a good discussion, and all the best in terms of your results ...
  13. TannerManner


    Feb 12, 2012
    I think the term "conical leveling" might need a little more explanation here. The words "single radius" and "cone" don't exactly work together.
  14. jesterbass


    Apr 20, 2007
    I believe your fingerboard will basically be a cylinder but with a cone "finish", it will not be a pure cone meaning compound radius.
  15. TannerManner


    Feb 12, 2012
    That really doesn't make any sense to me. Its a either cylindrical or a cone; cant be both. If you sand it so that is has a cone shape after giving it a single radius, its still a compound radius, just a different method.
  16. suraj


    Oct 1, 2008
    Mumbai, India
    Your right, Cylindrical will become conical with this kind of leveling.. Only difference will be that the difference between the two radii will be very small..

    Conical fretboards are designed in such a way that the fretboard thickness at the edge will be constant. But with this method, the edge will taper in thickness, with it being thicker at the nut. Note, i'm only talking about the edge of the fretboard..
  17. Musiclogic

    Musiclogic Commercial User

    Aug 6, 2005
    Southwest Michigan
    Owner/Builder: HJC Customs USA, The Cool Lute, C G O
    This is getting droal at best. Is the fingerboard tapered? Yep. Is a cylinder tapered? No. Do the strings follow differing angles along the radius? Yes. If leveling at varying angles to a cylinder are you moving cylindrically or conically? Conically. Thus to level the string paths properly along a cylindrical radius(non compound), you must do so in a conical fashion. Pretty simple to understand if you just look at it.
  18. Musiclogic

    Musiclogic Commercial User

    Aug 6, 2005
    Southwest Michigan
    Owner/Builder: HJC Customs USA, The Cool Lute, C G O
  19. Musiclogic

    Musiclogic Commercial User

    Aug 6, 2005
    Southwest Michigan
    Owner/Builder: HJC Customs USA, The Cool Lute, C G O
    This is also why there are so very few repairmen who do good fret jobs, because most who try to do fretwork have no understanding of it and thus spend hours to complete mediocre fret jobs.
  20. Bruce Johnson

    Bruce Johnson Gold Supporting Member Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    I think this discussion is getting confusing because you guys are missing one element. I'll try my hand at explaining the geometry here:

    First, a normal, typical bass fingerboard is cylindrical. That is, it has the same radius at the nut as at the heel.

    However, as described above, the strings aren't parallel. They are closer together at the nut than they are at the bridge. Even though the radius of the undersides of the strings may be the same at the nut as at the bridge, the underside of the strings actually describe a slightly different shape than a cylinder.

    The strings going right down the center of the fingerboard will be true. That is, if you lay a straightedge down the centerline of a normal cylindrical fingerboard, it will lay flat. However, as you move the straightedge off to the side at an angle to the centerline, following the actual paths of the outboard strings, you'll find that the center will be high. The straightedge will rock on a high spot in the center, as if the neck were backbowed. The further off-angle to the centerline you go, the worse this condition will be. Also, the smaller the fingerboard radius (rounder) is, the worse it will be. If you cut the fingerboard to a pure cylinder, you'll end up with high-spot buzzing on the outboard strings, but not the center strings.

    So how do you trim the surface of a cylindrical fingerboard to correct for this problem? The process is just like Musiclogic described above; you level-file right along the actual string paths, blending in between them. This process is often called "conical filing", but it isn't really forming a cone shape. That's what gets confusing. It's actually forming a slight "hourglass" shape. The radiuses at either end of the fingerboard are untouched. You are trimming away wood at the middle of the fingerboard (lengthwise), but only on either side of the centerline. So, the radiuses at the nut and the heel may be 12", but the radius at the 7th fret will be slightly less, like 11 3/4". I prefer to call this "hourglass filing" to minimize the confusion.

    On a fingerboard that has been properly "hourglass filed" like this, a straightedge placed along all of the string paths will be dead flat. When the straightedge is placed parallel to the centerline, but off to either side of center, there will be a slight gap under the middle, a "relief". But, down the center, there's no gap. This is where owners often get really confused when trying to check the relief and adjust the truss rod. A high quality, hourglass-filed fingerboard can give you confusing relief readings if you don't understand what you are looking for.

    If you want to get really technical, the real mathematical description of this hourglass-filed fingerboard is.....wait for it.....an offset hyperbolic paraboloid! I'm sure that brings back some frightening memories from your school days. Picture an hourglass, where you take the narrow waist and push it off to the side enough that one side becomes straight. That's what an "hourglass-filed" fingerboard looks like. The centerline of the fingerboard is right on that straight side. The further off to either side you go, the more hourglass-shaped it becomes. Try not to get a headache.

    So, how does this relate to compound radius fingerboards? A "compound radius" fingerboard is just another term for a conical-shaped fingerboard. That is, the radius is larger at the heel than it is at the nut. The surface is a section of a cone. Basically, the more conical you make the fingerboard shape, the less need there will be for the "hourglass filing" correction. There is a point where the surface becomes conical enough that no hourglass filing is needed. However, most commercial compound radius fingerboards aren't that radical, and still need a little bit of correction to make them flat along the string paths.

    What confuses things even more is that instruments built with compound radius fingerboards often also use a flatter radius on the bridge than on the nut. So, the underside of the strings are also on a conical shape, but they still aren't parallel, so the fingerboard surface still ends up needing some hourglass-filing correction. Don't hurt yourself picturing that one.

    How does this relate to frets? Exactly the same way. A really good fretjob has this hourglass-filing correction as part of it. The typical process involves using a straight file or diamond stick or oilstone, working along the string paths and blending in between. Leveling frets with sandpaper on a radius block is only a way of roughing them in. It takes an extra step to make them really true for the strings.

    Let me repeat: All of this hourglass-filing stuff becomes less noticeable and necessary as the fingerboard radius gets flatter (larger radius). A flat fingerboard doesn't have this effect at all. That's one of the reasons why manufacturers and builders like to go with flatter fingerboards; it's less complicated. I personally like to build my basses with very round fingerboards, from 7 1/4" to 4" radius. At a 4" radius, all of these geometry issues become much more obvious. That's why I've spent the time working with them and trying to understand them.

    I hope this helps clarify the discussion?
    Datsgor, mngnt, dune and 12 others like this.
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