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Even fretless fingerboard levelling tips
- Thread starter jesterbass
- Start date
Thanks. I couldn't think of a downside, but that doesn't mean there isn't one. When shaping a fingerboard by hand, it seems like a faceted fingerboard would be easier to do accurately, since you'd have the corners as an additional reference point. (If they aren't straight, you're off.)
A grooved fingerboard... another intriguing thought. If you machined a fingerboard with a ball end router bit, that would be a freebie, but then sanding might be a little more complicated.
I was thinking of that, but didn't know the term. Thanks.
Yes, that's true (literally and figuratively). Right down the center of the fingerboard, the string path will be straight and doesn't need any Hourglass correction. For both cylindrical and conical fingerboards. And on a flat (no radius) fingerboard, none of the string paths need correction.
The Hourglass correction is needed when the fingerboard has some radius (cylindrical or conical) and the string path is at an angle in relation to the centerline. Because of the tapering in string spacing between the bridge and the nut. The reason the Hourglass Correction is needed is complicated to explain, but it's simple to do once you understand the geometry.
On fingerboards, I use a razor sharp hand scraper plane and follow the string pathways. After planing, a slight sanding to remove any facets left behind.
After posting the pictures of my sanding boards on the last page, I realized that I'd been neglecting my two nice Long Boards. They could be really useful tools in my fingerboard leveling kit, if I just put some good sandpaper on them.
So, I ordered some rolls of 2 3/4" wide stearated sandpaper in 120 and 220 grit. One problem with the longer boards and beams is that they are too long for standard sheets of sandpaper. It's easier to buy it in rolls of the width to fit your boards and beams.
The grubby old long board is now wearing 120 grit, and the newer one is 220. I've got a bunch of ebony fingerboards coming up this summer and fall, so they are going to get some use.
So, I ordered some rolls of 2 3/4" wide stearated sandpaper in 120 and 220 grit. One problem with the longer boards and beams is that they are too long for standard sheets of sandpaper. It's easier to buy it in rolls of the width to fit your boards and beams.
The grubby old long board is now wearing 120 grit, and the newer one is 220. I've got a bunch of ebony fingerboards coming up this summer and fall, so they are going to get some use.
It would be interesting to watch someone who likes to bend the notes, only to have it fall into a trough between the strings!
That would be a good way to learn how pointless it is to bend on a fretless I guess.It would be interesting to watch someone who likes to bend the notes, only to have it fall into a trough between the strings!
Yeah, you could sell the grooves as a training aid, to help guitarists break old habits and become better bassists. Stay on your string path!
I once encountered this feature on a viola, also under the lowest string. This viola had a rather short scale, and if strung with standard strings the lowest string can get rather floppy. I believe the Romberg bevel was there to prevent the floppy string from rattling against the fingerboard.
I've never fully understood the reasoning for the Romberg Bevel on double basses. Other than tradition. Is it for fingering comfort? Allowing you to pluck the E string harder?
If the purpose is to ensure that the string path is true, why not cut similar "flat spots" on the other strings too?
As I understand it, it has more to do with arco than pizz.
I believe it’s a vestige of when loud strings weren’t developed yet and gut strings had to be bowed hard for maximum volume. The floppy gut E needed more clearance to play cleanly.
When I had new boards installed on my Kays I opted out of the Romberg Bevel. Most of the classical players I know play without one as well. Modern strings don’t need the extra room.
I never came across this thread before putting a new unlined ebony fretboard on my Mikro. I'd never done this kind of thing on a bass, but I had built a few rough as guts backyard cigar box guitars in the past and their diy fretboards, so I wasn't totally lacking in some rudimentary skills to do it. Due to poor eyesight, trying to judge levelness was a bit tricky. After I glued a rough cut out of the board on the Mikro and took clampage off and trimmed off excess board ( with a piece of hacksaw blade. Slow going pfewww!!) the board was a bit higher at the body and nut ends on the treble side. I decided to just eyeball the eveness after sanding with 200 and 400 paper. I did use a large rectangular shaped wooden trowel with paper . When things looked right I smoothed out a fair bit of scratches with 0000 steel wool soaked with mineral oil. Of course, after reading this thread, I realise there are more sophisticated approaches, which I will utilise if I did this again or need to do maintenance on the Mikro board down the track.
I haven't encountered any bumps or anything. The board is flat. I dropped the inner 2 nut slots down to the same depth as the outer too. The action at the 12th fret is 3mm on the bass side and 2.5 mm on the treble. I don't play with a delicate touch, so the height suits me good in low tension D standard
I haven't encountered any bumps or anything. The board is flat. I dropped the inner 2 nut slots down to the same depth as the outer too. The action at the 12th fret is 3mm on the bass side and 2.5 mm on the treble. I don't play with a delicate touch, so the height suits me good in low tension D standard
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I don’t know how I missed this thread the first time, still trying to get my head around it, the drawings really make it clear, or as clear as I’m capable of envisioning. TB Luthiers Corner Rules! Where else can you find this kind of advanced level discussion with advice from Pros?
An update on this subject:
You may have seen on my other threads that, over the last few years, I've been building up my collection of Pin Routers and learning how to use them. I'm in the process of switching my whole process of building my Scroll Basses over to being done with the Pin Routers, rather than hand routers. For various reasons.
Coming up, I'm going to be building up a special new fixture to do the fingerboard radiusing using a Pin Router. And I'm going to attempt to make the fixture so that it will cut the surface in the "hourglassed" shape. That is, it will cut straight surfaces down the string paths, not just small facets of a cylindrical surface like my current radiusing fixture. It will be a complicated fixture with synchronized Roll and Yaw axes. But I think I've figured out how to do it.
If it works, my fretless fingerboards will be cut to the final geometry, not needing the additional string path/hourglass sanding to true up.
You may have seen on my other threads that, over the last few years, I've been building up my collection of Pin Routers and learning how to use them. I'm in the process of switching my whole process of building my Scroll Basses over to being done with the Pin Routers, rather than hand routers. For various reasons.
Coming up, I'm going to be building up a special new fixture to do the fingerboard radiusing using a Pin Router. And I'm going to attempt to make the fixture so that it will cut the surface in the "hourglassed" shape. That is, it will cut straight surfaces down the string paths, not just small facets of a cylindrical surface like my current radiusing fixture. It will be a complicated fixture with synchronized Roll and Yaw axes. But I think I've figured out how to do it.
If it works, my fretless fingerboards will be cut to the final geometry, not needing the additional string path/hourglass sanding to true up.
This has been very informative @Bruce Johnson. Thank you very much. This explains why my fretless 5 requires higher action. Apparently, the fingerboard was not "finished." I may attempt to sand the string paths. It seems if I botch it, a luthier could still correct it. My recently acquired 6-string fretless is much better, probably due to a 47 inch radius.
An update to this classic old thread:
This week, I happened to be fitting a new fretless fingerboard on an Ampeg AMB-1 bass, including truing up the surface using the Hourglassing aka String Paths Sanding technique. The process which we described in mind-numbing detail in the first several pages of this thread.
So, for any of you who didn't fully absorb the math and geometry, here's some pictures of how I actually do the process:
Here's the neck with the new fingerboard glued on, and locked in my neck fixture. I've just used my router to cut the surface to a 7 1/4" radius. This is a cylindrical fingerboard, 7 1/4" radius on both ends and dead straight all the way down.
This is the same geometry as you would get by using a radius block to sand the surface. And this is how almost all electric bass fingerboards are cut and finished at the factory. Even most expensive hand made basses don't go any farther than this.
Hourglassing is a small correction which is done to the surface geometry of the fingerboard, after it's been cut to a Cylindrical or Conical (Compound Radius) shape. It's done with a long flat sanding board, not a radius block. Straight line strokes down the length of the fingerboard, but concentrating on the middle of the neck.
I've got 120 paper on the sanding board for the initial sanding. Then I switch to another sanding board with 220 paper.
Here's the secret of Hourglass sanding. With the flat sanding board on the radiused surface, I'm taking strokes right down the middle, straight in line with the centerline of the neck.
As I'm working off of the center, I'm gradually rolling the sanding board. And I'm also shifting it to a small angle in relation to the centerline. As I get over to the edge of the fingerboard, the side edge of the sanding board should be going approximately parallel to the side of the neck. This is the important part. Making the String Paths straight and flat.
Same thing on the other side of center; a gradual roll and shift of angle. It doesn't take very many strokes to get it trued up, because it's not removing very much wood. This fingerboard took me maybe 5 minutes of this sanding, 120 and 220.
And here's the fingerboard after the Hourglassing correction. It doesn't look any different, but......
If I put a straightedge right down the centerline, it's straight and flat, no gaps......
If I move the straightedge over to one side, but keeping it parallel to the centerline, there's a gap under it in the middle. Enough to slide a piece of sandpaper under.
But, if I angle the straightedge, in relation to the centerline, and set it right on the string path of the E string, there's no gap. The path directly under the string, is flat.
And that's what this Hourglassing stuff is all about. It's a small correction to make the String Paths flat under the outboard strings on a fingerboard that has a moderate radius.
I did not change the shape of the surface into a Conical or Compound Radius. It's still Cylindrical, 7 1/4" radius at both ends. The Hourglassing correction sands away about 0.004" off the surface, but only in the middle of the neck, on either side of the center. I barely touched the two ends.
If I had cut this fingerboard to a Compound Radius, like 7 1/4"-12", I would do the Hourglassing correction by the same method. And the fingerboard would still remain 7 1/4"-12" Compound Radius. But its String Paths would be flat.
The result of making the string paths flat is that the action can be lower, and any buzzing or Mwah will be more even up and down the length of the fingerboard.
Hourglassing/String Path Sanding isn't absolutely necessary on a fretless bass, but it's an improvement over what you get from the factory.
This week, I happened to be fitting a new fretless fingerboard on an Ampeg AMB-1 bass, including truing up the surface using the Hourglassing aka String Paths Sanding technique. The process which we described in mind-numbing detail in the first several pages of this thread.
So, for any of you who didn't fully absorb the math and geometry, here's some pictures of how I actually do the process:
Here's the neck with the new fingerboard glued on, and locked in my neck fixture. I've just used my router to cut the surface to a 7 1/4" radius. This is a cylindrical fingerboard, 7 1/4" radius on both ends and dead straight all the way down.
This is the same geometry as you would get by using a radius block to sand the surface. And this is how almost all electric bass fingerboards are cut and finished at the factory. Even most expensive hand made basses don't go any farther than this.
Hourglassing is a small correction which is done to the surface geometry of the fingerboard, after it's been cut to a Cylindrical or Conical (Compound Radius) shape. It's done with a long flat sanding board, not a radius block. Straight line strokes down the length of the fingerboard, but concentrating on the middle of the neck.
I've got 120 paper on the sanding board for the initial sanding. Then I switch to another sanding board with 220 paper.
Here's the secret of Hourglass sanding. With the flat sanding board on the radiused surface, I'm taking strokes right down the middle, straight in line with the centerline of the neck.
As I'm working off of the center, I'm gradually rolling the sanding board. And I'm also shifting it to a small angle in relation to the centerline. As I get over to the edge of the fingerboard, the side edge of the sanding board should be going approximately parallel to the side of the neck. This is the important part. Making the String Paths straight and flat.
Same thing on the other side of center; a gradual roll and shift of angle. It doesn't take very many strokes to get it trued up, because it's not removing very much wood. This fingerboard took me maybe 5 minutes of this sanding, 120 and 220.
And here's the fingerboard after the Hourglassing correction. It doesn't look any different, but......
If I put a straightedge right down the centerline, it's straight and flat, no gaps......
If I move the straightedge over to one side, but keeping it parallel to the centerline, there's a gap under it in the middle. Enough to slide a piece of sandpaper under.
But, if I angle the straightedge, in relation to the centerline, and set it right on the string path of the E string, there's no gap. The path directly under the string, is flat.
And that's what this Hourglassing stuff is all about. It's a small correction to make the String Paths flat under the outboard strings on a fingerboard that has a moderate radius.
I did not change the shape of the surface into a Conical or Compound Radius. It's still Cylindrical, 7 1/4" radius at both ends. The Hourglassing correction sands away about 0.004" off the surface, but only in the middle of the neck, on either side of the center. I barely touched the two ends.
If I had cut this fingerboard to a Compound Radius, like 7 1/4"-12", I would do the Hourglassing correction by the same method. And the fingerboard would still remain 7 1/4"-12" Compound Radius. But its String Paths would be flat.
The result of making the string paths flat is that the action can be lower, and any buzzing or Mwah will be more even up and down the length of the fingerboard.
Hourglassing/String Path Sanding isn't absolutely necessary on a fretless bass, but it's an improvement over what you get from the factory.
That's an excellent demonstration and explanation, Bruce. I really appreciate the time and effort you took to do it.
