Fretboard shaping (ruled surface) jig

[Louie Atienza]

In earlier posts I've covered my thoughts on this topic, including the "mathematics" behind such a fretboard, and examined the jigs and techniques currently used.

While there are many jigs that do produce a true "conical" surface, they may not necessarily produce what might be called a "ruled" surface, that takes into account the actual taper of the outermost strings. In any fretboard where all "string lines" lay flat, the "radius" will change in direct proportion to it's distance from the point where the lines of the two outermost strings converge.

An important thing to note is that if you want to keep a constant fretboard "edge" height, you would either have a board that tapers in thickness, or you'd end up with a radius at the heel that's flatter than what the fretboard taper would suggest. If you use a "swingarm" style jig, and pick an end radius that is flatter or more arched than suggested by the string taper, you will find that there still will need to be shaping, so that all string paths remain flat.

To address this issue, I have developed a fretboard "shaping" jig that DOES take the fretboard taper into account, because the jig actually pivots off the theoretical convergence point of the outermost strings. Instead of using the fretboard end radius, my jig uses the actual bridge radius, so that is predetermined based on player preference, feel, etc. I say "shaping" instead of radiusing, since in theory the jig will work with any (reasonable) nut and saddle shape, even if one were convex and the other concave. I actually used this to effect in the last instrument challenge, where I created a twisted fretboard surface.

I need to take more pics of the jig in action, but here are a few to whet the appetite. In this pic the two lines depice the fretboard end and nut, respectively. The router carriage is affixed to two lengths of wood beams that extend to the convergence point, where it pivots on a steel rod.

[Louie Atienza]

Here is a view from the pivot point. The round part under the jig is 1" in diameter, and there is one on the other side of the carriage, where the theoretical bridge is. What makes this jig work is that both these "followers" are identical, and the same cross section as the 1" core box bit in the router. The bit is also set at the same "depth" as these two followers. In this way, the carriage can be tilted and still produce an accurate cut. If your start and end radius aren't too drastic, even a straight bit would work (and probably cut faster) and the jig design itself would prevent the corner from digging. Since the "nut" side template is a distance from the nut, it's radius needs to be calculated, though it's rather easy to do. To keep the fretboard edge the same height, you would have to layout the guide templates so that the heights are the same at the bridge and nut widths.

It should be clear to see how a twisted board could be produced, simply by making "canted" templates. This would necessitate using a round bit.

I have been unexpectedly busy, but hopefully this weekend I can post better pics and explanations for this system, and hope it will be of use to those seeking another way..

[Louie Atienza]

Here's the fretboard form the last challenge, which has a 10"-14.6" compound radius, AND is twisted 5.5 degrees (1.5 to the left at the fretboard end, and 4 at the nut) for a total of 8 degrees from bridge to nut. This is also a multi-scale fret arrangement as well...

[Jason Rodgers]

YES, this is what I want to see!

[Ron Belanger]

I'm still a little confused, but that is not unusual. I'm looking forward to more pics.

[Louie Atienza]

I have to make some fretboards this weekend, so I will get some shots then. I'll also explain some of the mathematics behind it, but I promise, it's really simple. If you can cross-multiply, or do ratios, it's almost trivial.

I thought I'd obsolete this jig since I have a few different profiles drawn in CAD for the CNC machine, but quite honestly, this is much faster than turning on the computer, controller, installing my fixture on the table, drill and countersink mounting screws, etc, etc. Might be a different story when I get my vacuum hold down going.

Murray, where are you?!

[Andy Birko]

Might be a different story when I get my vacuum hold down going.

It will be. Vacuum hold down is totally where it's at. It takes me less than 30 min total to radius, profile and slot a fretboard start to finish. Add about 5 to 10 minutes to mount the fixture to the machine if it's not already there.

[Mario Proulx]

I had some really nice custom machinery made to help with fretboards, and one of them was a vacuum hold down, but even with a simple fridge pump it was distorting the fretboard blank noticeably, negating any accuracy benefits from the rest of the jiggery. Vacuum is strong! And relentless! So I reverted back to double-stick tape and haven't looked back once. Sometimes, many times, often times, simpler is better...

[Nelson Palen]

Controlling the vacumn can minimize distortion when the workpiece isn't "perfectly flat".
This can be done with a bleeder valve to regulate the vacumn with the pump running.

edit: A flat sanding or jointing operation on the top or bottom of the fretboard prior to thicknessing will leave the board fairly flat, however.

[Louie Atienza]

Might be a different story when I get my vacuum hold down going.

It will be. Vacuum hold down is totally where it's at. It takes me less than 30 min total to radius, profile and slot a fretboard start to finish. Add about 5 to 10 minutes to mount the fixture to the machine if it's not already there.

I got you by a few minutes... Pics coming tomorrow,

I just don't trust double-stick tape on the CNC, so what I do (for boards with fret dots) is drill a pilot hole through at the 5th and 15th fret dots, and run a #4 screw through to my fixture. Instead of using a drill operation to cut my fret dot holes, I use a 1/8" endmill and pocket them out; I get a nice pess-fit tolerance with the wood dots I use.

On my jig, I've had success with double stick tape.

[Andy Birko]

it was distorting the fretboard blank noticeably, negating any accuracy benefits from the rest of the jiggery.

Sounds like the fixture wasn't well designed. There should be enough support built in to the fixture so that it doesn't distort when it's holding the workpiece. If it is distorting, it needs more support. Got a pic?

[Andy Birko]

I got you by a few minutes... Pics coming tomorrow,

Radiusing and slotting a FB without CNC in under 30 min is very impressive. Granted, there's only about 3 or 4 minutes of hands on time with the CNC, you still have to be nearby to change tools.

[Louie Atienza]

I got you by a few minutes... Pics coming tomorrow,

Radiusing and slotting a FB without CNC in under 30 min is very impressive. Granted, there's only about 3 or 4 minutes of hands on time with the CNC, you still have to be nearby to change tools.

I used to use the StewMac jig for slotting, but I find doing it with a shop-made "square" made from scrap, and the stewmac pullsaw with a depth stop screwed on, works very fast. I slot after shaping, this way theslots follow the board radius. (I think I saw a video of Mike DeTemple doing then this way.) With a straight bit, the radiusing goes fast, maybe about 5 minutes, and it comes out pretty clean.

For CNC I use a .024" endmill to do the fretslots, and run it at 60-70ipm and .027" doc, 25 degree rampin at 30ipm. The fretslots follow the fretboard radius and stop short of the edge. With fret dot markers, I use a 1/16" endmill to cut the 1/4" pockets for the dots, as well as through holes for screws to hold down the fretboard, ast the 5th and 15th frets. I also use the 1/16" endmill for the nut slot, "faux" binding, and for cutting out the board shape, saving time for tool changing. I also went from a 1/4" to 3/4" ball endmill for the final fretboard shaping, and use a 3D offset strategy instead of a raster or parallel toolpath, shaving more minutes off. So even with the tool changes, I'm at about 20 or so minutes. I need to make a "gang" fixture so I can do multiple boards at a time, which would save even more setup time.

[Andy Birko]

20 minutes is pretty dang fast.

What kind of stepover are you using for the radiusing?

[Louie Atienza]

20 minutes is pretty dang fast.

What kind of stepover are you using for the radiusing?

I rough with a straight bit, and finish with a bullnose. If possible, always rough with a straight bit; because it is always faster and more efficient; you have 28% more cut on a 1xd doc vs. a ballnose bit.

I have the stepover at 50%, though my CAM does "step reduction," where it will step down to my mac cutting depth, then come back up to make smaller stairsteps (I reduce the stairsteps to .04").

For the finish pass I use a 3D offset strategy. I don't set it for stepover, rather I set it for max scallop height (about .01"). I use OneCNC XR4 Mill3D Expert, though XR5 just came out with a better CAD side.

[Louie Atienza]

I had some really nice custom machinery made to help with fretboards, and one of them was a vacuum hold down, but even with a simple fridge pump it was distorting the fretboard blank noticeably, negating any accuracy benefits from the rest of the jiggery. Vacuum is strong! And relentless! So I reverted back to double-stick tape and haven't looked back once. Sometimes, many times, often times, simpler is better...

I wonder if the seals protruded out too much, or the vacuum phlenum was not perfectly flat, that would cause the fretboards to distort?

On my manual jig and CNC fixture, I leave the fretboard about 3/4" long on both sides; and this allows me to screw down the blank. The CNC misses the screws completely, and on the manual jig I use stops to limit the router's travel.

My darn computer/camera cable is not working, so I have to figure a way to get these pics on the computer...

[Nelson Palen]

I have to wonder if a faceted fretboard would make sense in the world of CNC.
By faceted I mean that each string would have it's own flat surface.
Sure would open a brand new can of fret bending and dressing worms.

[Louie Atienza]

I have to wonder if a faceted fretboard would make sense in the world of CNC.
By faceted I mean that each string would have it's own flat surface.
Sure would open a brand new can of fret bending and dressing worms.

We could go one step further and make the frets under each string a different radius. Or even have six mini-frets, and fan each one out. This way we could optimize the bending properties of each string!

I've actually considered doing a faceted fretboard. Not of use if you're a blues guy, but maybe to jazz and chickn' pickn' folk...

With CNC (or even my manual jig) it's even possible to do a constant-radius, ruled surface, or even a reverse-compound or even go from convex to concave!

[Andy Birko]

For the finish pass I use a 3D offset strategy. I don't set it for stepover, rather I set it for max scallop height (about .01"). I use OneCNC XR4 Mill3D Expert, though XR5 just came out with a better CAD side.

That's kind of what I figured. I'm using a much tighter stepover (.008" if I recall) so there's very little sanding necessary off the machine. I tried using a larger stepover and the max scallop height thing which made for a much faster machining time but I just wasn't satisfied with the finish.

I might have to try the equidistant offset idea. I'm currently using raster but constrained to just larger than the FB profile (and at 400ipm) so I'm not sure I'll get that much time saving but it could shave off a minute or so.

[Louie Atienza]

For the finish pass I use a 3D offset strategy. I don't set it for stepover, rather I set it for max scallop height (about .01"). I use OneCNC XR4 Mill3D Expert, though XR5 just came out with a better CAD side.

That's kind of what I figured. I'm using a much tighter stepover (.008" if I recall) so there's very little sanding necessary off the machine. I tried using a larger stepover and the max scallop height thing which made for a much faster machining time but I just wasn't satisfied with the finish.

I might have to try the equidistant offset idea. I'm currently using raster but constrained to just larger than the FB profile (and at 400ipm) so I'm not sure I'll get that much time saving but it could shave off a minute or so.

I could run a smaller stepover, but since I prefer to do the final trueing by hand, getting smaller scallops didn't matter too much. My machine will do 400ipm on the y but the x is limited to 200. Raster is good if your surface is rectangular in nature, but since the board is tapered, you have to make the cutting boundary larger ato allow the change of direction and still machine the board surface. With offset, it will follow the edge of the board on both sides, so there's far less air time. And at .008" stepover, that airtime adds up!