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Sanding fretless neck - still have issues

Discussion in 'Hardware, Setup & Repair [BG]' started by -Asdfgh-, Jun 6, 2015.


  1. -Asdfgh-

    -Asdfgh-

    Apr 13, 2010
    UK
    I have two electric fretlesses - an old Tokai currently strung with TI flats with a 1.5mm E string at 12 fret action. Very smooth and nice. This has markers in a rosewood fingerboard. The other is a Squier VM as a backup, which has an ebanol board with markers.

    With the VM to start with the markers were slightly proud, which was easily solved with a sanding beam and some sandpaper stuck to it, straight neck, and I did some work on smoothing it out, with the truss rod slackened off. I've spent a fair bit of time working on it over the past couple of years. The action is currently set to around 1.7mm with .100 to .40 Dunlops for a brighter sound than the other bass. There are still a couple of positions where there is excessive buzz, e.g. 5th position on the A, unless I am very careful about the position. E.g. if my finger is dead on position there is no excessive buzz, but a couple of mm off (as happens sometimes) and slightly behind the position it buzzes. Mwah is generally good, with a couple of minor spots up the neck where there is a little too much relative to close positions.

    Any recommendations, or is it a case of just sanding a bit more (I generally don't take much off during any sanding episode)? There is no obvious dip in the fingerboard in that area.
     
  2. -Asdfgh-

    -Asdfgh-

    Apr 13, 2010
    UK
    Ok.. answering my own question...

    I ran fingernail up and down the neck and the spots where there is some extraneous buzz are spots where my fingernail drags as they go over the fretmark inserts. So despite the various hours I've put in I've been so gentle as to not quite flatten the fingerboard over those spots. If my action was higher (or maybe strings thicker) it probably wouldn't be noticeable.

    So it will be time to get the sanding beam out again.

    It's nearly there...
     
  3. -Asdfgh-

    -Asdfgh-

    Apr 13, 2010
    UK
    P.S. otherwise, in terms of feel, it's now nice to play. I was previouly a bit unhappy with ebanol until I made it just a shade more matt by not doing a final buff after sanding.
     
  4. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism Supporting Member

    Are you sanding with a flat block or with a proper radius block? I am pretty sure the VM jazz is 9.5".
     
  5. -Asdfgh-

    -Asdfgh-

    Apr 13, 2010
    UK
    The approach I've most read about before is using a long metal bar with paper attached (about 18") which is what I used on this bass and on the Tokai at various points, and it has worked perfectly on the Tokai which I couldn't be happier with. I don't think the issue is radius (but maybe it is wise to get a 9.5" radius block - everything I have is 9.5" radius apart from my acoustic) too. I think the issue is the fretmarker inserts that I had thought (with a finger touch) were fine before, but the fingernail trick revealed it wasn't. Now, of course, I can feel where the fretmarkers are just with my fingertips. I'd spotted this issue when I'd bought it, hence the previous sanding which improved the ability to take a really low action enormously but seemingly I haven't quite done it enough. The buzz wasn't so bad before but I was trying to tweak it to be as silky to play as the Tokai.
     
  6. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Truing up a fretless bass fingerboard is a fussy, tedious job. It takes time and patience. You are basically using the right technique, but I'll add a few tips and details:

    First, you should be leveling the fingerboard with the truss rod partially tight; snugged up enough that the neck begins to bend backwards. Keep the neck in that condition while you trim the fingerboard to be flat. That's very important for the stability of the neck.

    Second, radius blocks can be used to shape the basic radius of the fingerboard, if you are making up a new fingerboard. But you don't need one. You can shape a radius with a flat sanding block and a radius gauge. I have a nice set of radius blocks that I bought 20+ years ago, and I hardly ever use them.

    Third, you should NOT use a radius block for the final truing of a fretless fingerboard. The perfect shape of a fingerboard is not a section of a cylinder, nor is it a section of a cone. It's more complicated than that, because of the taper in the spacing of the strings between the nut and the bridge. There was a thread here on TB about two years ago, where we went through all the geometry in great detail. I'm not going to repeat all that here, but basically, if you true the fingerboard with a radius block, you will end up with high spots in the middle of the neck, on the outboard strings. It isn't obvious right away, but the true shape needed is a slight hourglass shape. And this has nothing to do with relief.

    Here's the thread, if you want to get into the details. The 2nd and 3rd pages are where we really get into the geometry.
    Even fretless fingerboard levelling tips | TalkBass.com
    Yeah, I know, all that geometry stuff can give you a headache. But the right technique for truing up a fingerboard is actually fairly simple, and close to what you are doing. Use a straight flat block, going right down the individual string paths. The string path is the 1/4" wide strip of wood that is directly underneath each string. Make those paths straight and flat down the whole length of the fingerboard. You should be able to put a 24" straightedge on each path, and not see any lumps or gaps. That's what's critical to the fingerboard: getting those string paths straight.

    Once the string paths are true, you gently round off the areas between the paths. Do this carefully, to avoid touching the paths. This is just for looks, really. The wood between the paths never touches the strings. Concentrate on keeping the paths straight and flat.

    All of this is harder to describe than it is to do, but you should understand why it needs to be done this way.
     
    SherpaKahn and rockelye like this.
  7. -Asdfgh-

    -Asdfgh-

    Apr 13, 2010
    UK
    Thanks for that. Very helpful.

    I'd certainly agree that it is tedious, and with ebanol much messier than rosewood, it seems.

    I'd read that thread first, and it seemed to confirm what I was doing was along the right lines, as you say, but I was just confused it wasn't having quite the right effect. I hadn't concentrated the string paths per se, so that I need to look at. Hopefully I just need to go a little further given the main spot of contention is on an inner string (plus a little on the G). They are all mid neck length so maybe the issue is having the truss rod a little too slack too.

    It's a movement of 2mm at most on the finger position that takes the sound from fine (mwah but no choking out) to pretty horrible, and that's from perfectly on top of the marker to being a shade behind it. I just thought I'd smoothed it out and with flats it seemed it was, but the rounds say not.
     
  8. rogerb

    rogerb

    Aug 31, 2010
    Radius sanding block solved all my woes. Makes it WAY easier, not foolproof, but almost. Sure it could be possible with a bar... but... for the price of the radiuses sanding block it isn't worth the fight. I had like a little ski jump (or extra epoxy!) in the upper frets happening too, but I fixed that up as well.
     
  9. megafiddle

    megafiddle

    May 25, 2011

    There's something important to realize - If a long leveling beam is used, and it is wide enough to insure that the beam edges do not hit the fingerboard, the line of contact between beam and board will remain parallel to the board centerline. You cannot force the line of contact to become angled simply by angling the beam.

    As long as the line of contact remains somewhere within the plane surface of the beam, it will always run parallel to the axis on a cylindrical surface.

    -
     
  10. -Asdfgh-

    -Asdfgh-

    Apr 13, 2010
    UK
    The block I've been using is a little less than an inch (probably 2cm) so the edges don't contact the board.
     
  11. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    Well, that's the point that we went over in that thread that I linked to. If you use a long flat beam and keep it parallel to the centerline, rather than following the actual angled string paths, then you won't get a true fingerboard surface. You'll get a cylinder, and the outboard strings will have high spots in the middle of the neck. Same thing if you use a radius block; it makes a cylinder. That's not what the strings need. The purpose of using a long flat beam is to make it follow the actual string paths, and make those paths flat. When you do that, the final shape isn't a cylinder or a cone.
     
  12. megafiddle

    megafiddle

    May 25, 2011
    But it doesn't matter whether you keep it parallel to centerline or not. You can't angle the line of contact by using a plane surface on a cylinder.

    Try it - hold a wide flat length of wood against the side of a soda or beer can; no matter how you angle the wood, the line of contact does not change.

    You have to deliberatly work on the "hump" locally for an hourglass contour, or change the end radii for a conical contour.

    -
     
    Jgdpanzer likes this.
  13. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    I don't want to rewrite all this, so I'll cut and paste these posts of mine from the other thread:

    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?
    Here's a follow-on post, relating this discussion to the truing of upright bass fingerboards:

    Yeah, upright bass fingerboards really exaggerate all of this geometry. I do a lot with hot rodded Baby Bass necks. Dramatic conical fingerboards, combined with a wide taper in the string spacing and relief cuts that have to rotate around the cone! Shaping out an upright bass fingerboard is a lot harder than most people understand.

    You've got to keep the terminology straight though:
    Doing an "hourglass" trim does not, by itself, change a cylindrical fingerboard into a conical fingerboard. You can do an hourglass trim on a cylindrical fingerboard, or you can do an hourglass trim on a conical fingerboard.

    If you're changing a cylindrical fingerboard into a conical (or "compound radius") fingerboard, that would correctly be called a "conical trim". You are changing it into a cone, so that the radiuses are now different at the two ends.

    Upright bass fingerboards start out as a conical shape, around 2 1/2" radius at the nut and 4" radius at the heel. To true it up for low action, it needs to be "hourglass filed", which makes the middle a little skinnier, but doesn't change the radius at either end. That would correctly be called an "hourglassed conical" fingerboard.

    Now, most electric basses have cylindrical fingerboards, with the same radius on both ends. To trick it out for low action, you can "hourglass file" it. But that doesn't make it into a conical (compound radius) fingerboard. It just makes it into an "hourglassed cylindrical" fingerboard.

    Of course if you want to, you can do both: First "conical file" it to convert it from a cylinder into a cone (that is, making it into a compound radius fingerboard), then "hourglass file" it to correct for the taper in string width.

    Is that more understandable?

    I know this all sounds complicated, but it comes down to the same basic thing: In terms of playability, the only thing that matters is the 1/4" wide strip of wood directly underneath each string. The rest of the fingerboard is just there for decoration. That's what Big B is doing with his technique with the jointer: Get the string paths straight, and then blend off the excess between them.

    A few years back, I worked on some really radical instruments that had reverse compound fingerboards! They were 7 1/4" radius at the nut and 2 3/4" radius at the heel, if you can imagine that. Six strings, short scale length. The fingerboard geometry was crazy. They required a significant amount of hourglass filing, close to 1/8" off in the middle of the fingerboard. As I mentioned above, the more radical the radius, the more hourglassing is required. For those necks, I ended up making a special router fixture that cut six round-bottom flutes directly along the string paths. Once those paths were created, I would round off the spines between the flutes. It was surprising how hourglassed the final shape of the fingerboard was.​
     
  14. megafiddle

    megafiddle

    May 25, 2011
    I understand exactly what you are saying about the geometry of the hourglass shape. Sorry I wasn't clearer about that. I came up with the same shape myself a few years ago, when I calculated the size of that "hump" at the fretboard edge, and presented it on another forum. I also claimed there that you could simply angle the leveling beam to match the string angle, and remove the hump. I discovered by the end of the thread that it doesn't work with typical (relatively wide) leveling beam. The topic was basically about a conical shape being required to eliminate that hump, and my point was that it could be done with a very minimal amount of wood (or fret) removal. I believe I called it a "saddle" shape, but it is the very same hourglass shape that you refer to. For a Fender electric guitar, the hump is on the order of about 0.001". My argument was, just remove that tiny hump if you really want the board straight, or simply let it get lost in the relief.

    But this is about achieving that hourglass shape.

    Now you can do it if your leveling beam is narrow enough. But initially, as you begin cutting, the ends of the leveling beam will necessarily not be in contact with the ends of the fretboard (or fingerboard). So you are in effect, spot leveling, with just the central region of the beam. Also you will necessarily be hitting the board with the edges of the beam, and risk gouging it.

    I brought this whole thing up because someone using a leveling beam is likely going to make sure that all the cutting is done within the flat surface of the beam. You don't want the edge of the beam to contact the board because of the danger of gouging. And as long as you keep the contact within the edges of the beam, on the flat surface, you cannot affect the path that you are cutting! It will always be parallel to the centerline. You can angle the beam when working near the board edges, but you are not cutting where you think you are.

    Again, and this is important, this refers to a beam that's wide enough to always maintain contact along all or most of the fretboard length, and always on the flat surface of the beam (and not run off the edge). But I believe such beams and uses are common. When you angle such a beam, all you are really doing is moving the edges of the beam in relation to the line of contact. The line of contact is still parallel to the centerline of the fretboard. It is just no longer running down the center of the beam.

    It is ridiculously simple to try it with a flat piece of wood and a beer can. No excuse not to try it. It demonstrates what I am trying to say perfectly.

    -
     
    Last edited: Jun 15, 2015
  15. -Asdfgh-

    -Asdfgh-

    Apr 13, 2010
    UK
    I may get round to doing this at the weekend. If I do, I will report back.
     
  16. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    A thorough and beautiful post, Bruce.

    Sometimes I wonder, though, if we aren't chasing esoterics for clinical accuracy while putting aside some basic truths. First, we are working with wood which is inherently unstable. We can mill it to a very fine accuracy that will be gone when the weather changes. Then we are compounding the problem by trying to achieve the lowest possible action for a purpose that may not be well-defined. Sure we want our instruments to play the best they can, but it hasn't hampered many a fine instrumentalist from producing wonderful music on an instrument we would deem to be nearly unplayable. Most of the pro's that I work with don't care much about the nth degree of playability so long as they don't get buzz. And for most of them they are very happy with high action. They are amazed with my basses when they try them, but they don't want their instrument set up like that for two very important reasons. First, they have to be able to play their instruments cleanly all over the world in vastly different climates without having to tweak and fiddle constantly. And secondly, since most of them play both electric and string bass, they don't want to have to dramatically adjust their playing technique moving from one instrument to another.

    You and I will continue to provide very finely tweaked instruments because we can do it. And I am so thankful when I get a client that appreciates my obsession.

    Not trying to discount what you said in the post above. Just rambling on and questioning why I bother. Well, I know the answer to that, as do you.
     
  17. -Asdfgh-

    -Asdfgh-

    Apr 13, 2010
    UK
    In my case it is getting the same low action as on the other fretless. That was orginally strung with rounds which chewed up the fingerboard 20 years ago. It got treatment from a luthier followed by some tung oil and some top-up sandings since. 1.5mm at the 12th fret E, no extraneous buzzing, with plastic fret markers.

    I am trying to get the VM Jazz to a similar level, albeit with rounds which do have a different vibrational modes, so it might be a tougher job. With the action set to around 1.6mm, maybe 1.7mm, it plays well in most positions, apart from one (D on the A string) which buzzes a lot. That actually seems to be related to the plastic fret markers. The fingerboard wasn't quite to the standard I like when I got it, but not too bad, but the fret markers were the main issue, and I suspect I have just not quite sanded them enough and/or not quite sanded enough overall, or had the truss rod just a little too slack.

    I know what I am trying to achieve, though, which is eliminate that main buzz and a few others which seem to match with where the fingerboard isn't quite perfect over the fretmarkers. As noted above when I run my fingertip over everything seems fine, but I notice there is discontinuity if I use my fingernail, which I wish I had done before.

    In terms of stability, it seems rock solid over the sort of seasonal variations here. I actually had one bass in storage for a year (not this one) and when I got it out of the case it was still in tune.

    But I'll give the bass another going over this coming weekend. It just takes a while to mask it all off, take off the strings, pop the nut off, adjust the truss rod, etc.!

    But thanks for all the comments as it has helped.

    I have done one other adjustment to it, which is change the push-pull series-parallel switch for a push-push one so now I don't pull the knob off when engaging series mode!
     
  18. Turnaround

    Turnaround Commercial User

    May 6, 2004
    Toronto Canada
    Independent Instrument Technician, and Contractor to Club Bass and Guitar - Toronto
    Yes, in your case I don't think we are talking about esoterics. And since the board is ebonol, you won't be dealing with the same level of "instability" as you might with a wood 'board. Keep at it, you should be able to get past the problem at the edges of the markers.
     
  19. wraub

    wraub

    Apr 9, 2004
    ennui, az
    previated devert
    A brief note, if I may: Please listen to Mr. Johnson on this one.
    I followed his posts in that previous thread, and got my long difficult fight of a fretless conversion to play like a factory fretless.
    The fretless board needs the hourglass shape he describes. Follow the string paths, and all will be well. ;)
     
  20. -Asdfgh-

    -Asdfgh-

    Apr 13, 2010
    UK
    I still sometimes wish I'd picked up another Tokai rosewood fretless, though.... but the ebanol is another voice on a backup bass.
     

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