Fanned Fret Slotting Sled

[Paul E Buerk]

I finally got around to designing, building and testing out a sled for cutting fanned fret slots. The concept is extremely simple, and it seems to work just fine. There's nothing exceptional about the sled itself, but it's dead simple to use.

The fingerboard blank is held against the sled base with a couple toggle clamps. These two are a couple I picked up from Harbor Freight. Some 120 grit sandpaper helps hold things in place. The bolt and rubber caul on the clamp aren't really long enough, so I ended up using a washer and a magnet on top of the blank to add a little more pressure. The combination had no problem holding things in place.

For lack of a better term, I included an aiming reticle by epoxying it on top of the clamp riser bases, and the clamp screws go through the base of the clamp, the reticle, the risers, and the base. I then ran the sled through a few times, gradually raising the blade until it just scratched the surface of the plastic. The bottom of the sled has a slot routed in it to accommodate the blade and stiffeners. The risers are roughly 1/4", so a 7/32" thick fingerboard fits nicely under the reticle. There are two holes in the plastic for the clamp cauls to go through.

I found a website that does all the calculations for practically any fingerboard, and the best part is that it can kick a file out in .dxf. I can pull that file into DraftSight, and from their export the drawing as a PDF after it's cleaned up a bit. Took it to Staples and had them print out the PDF, checked the dimensions which were spot on, then applied the mirror-imaged printouts to the blank with a piece of doublesided tape. Ran some additional transparent tape along the edges to hold it down.

To use it, just line up the lines on the template with the saw line on the reticle, clamp down, and cut. The toggle clamps swing out of the way easily, making it easy to see how everything is lining up.

This may not be as accurate as a CNC rig, but it seems to me that it's probably more accurate than a mitre box made from sections of aluminum angle. Any criticism, though, is welcome.

[David King]

Paul, I like it. It's an improvement on Doolin's miter saw setup.
So you need a mirror image on paper of the final fingerboard?
Fretfind2d can output single or multipage pdfs saving you a step.

If you were going to make a permanent and idiot proof jig you could have a two sets of holes drilled into the top of your sled such that your fingerboard blank would drop into each position via pins in each end of the FB . Each pair of pin holes would line up one fret perfectly with the blade. There must be a formula for determining the hole locations which could then be drilled once on a CNC router. This would only be necessary for repeatability in a production setting but it's something I've been thinking about doing.

[Jason Rodgers]

When you say "it seems to work," do you mean that you've cut and used a few fretboards with intonation success? If so, then I'll agree that it looks simple and effective.

I've pondered a bit on such a sled, and the solution I came up with is basically what you've done, but using two of those notched scale registering templates on either side of the fretboard (or one template with the desired treble and bass scales, perpendicular fret, and taper) with registering pins in line with the blade path. This takes the eyeball out of the equation. You simply double-stick tape the template on the center line (or separate templates along the taper), plop the template and fretboard package down on the registering pins, zip, rinse, repeat.

Using separate templates for treble and bass would allow for a wide variety of spreads, easily adjusted perpendicular fret, and any taper. Also, if the templates are off the ideal relationship alignment by a smidge, each is still accurate and a straight line between them will still result in correct temperment (even if intonation needs to be tweaked at the bridge).

Your toggle clamps are a feature that I had not considered, though. Good on ya, gettin' jiggy wit' it!

[Edit: I see David was typing at the same time, with similar thoughts.]

[Paul E Buerk]

Fretfind2D is awesome. I think it's saved me at least a week of design time based on my previous attempts to model it in Rhino. I only kick it out to .dxf so that I can take out the extra length of the strings and clean it up a bit. Also put in a reference rectangle so that I can verify the 1:1 scale, at least down to a 100th of an inch.

I'd thought about using the two reference pin idea and it seems absolutely appropriate, that is if I had a CNC. It would be easy to draw it up, just harder to execute by hand. If I had a CNC or laser, I'd probably make the templates that way, even if it was just with this jig as is, and scale up the clamp riser to match.

When I say "seems to work", I just mean that it measures out correctly. If I'd done several fretboards, I'd just say it works.

[David Robinson]

Paul - this great I am finishing up my fanned fret sled, but it was getting too complex (laser sites and too many knobs) I think I may just be "inspired" by yours.

[Andy Birko]

ould be easy to draw it up, just harder to execute by hand. If I had a CNC or laser, I'd probably make the templates that way, even if it was just with this jig as is, and scale up the clamp riser to match.

If you had a CNC, you wouldn't need templates

[Paul E Buerk]

Not necessarily. I was surprised how fast it was to cut slots using this jig.

[Andy Birko]

It's not even the speed that would concern me as there's very little time to be made up over a CNC machine in cutting the frets unless you're using a gang saw but that won't work on a fan fret anyway. My spindle is too slow to do it (limited to 18k) but a friend with an air spindle at 80k rpm and a 3 flute bit (I use 2 flute because they're cheaper) can slot a fretboard in just over one minute (if you do the math you can figure out about how long it takes me to do it)

More important to me would be that with the CNC, you can profile, radius and slot in one setup with an accuracy that would be pretty difficult to achieve even with well made templates and jigs.

Whether or not a few thou here or there are going to affect the final intonation of the instrument is debatable but at least it's one less thing to worry about.

Still a cool jig.

[Dave Higham]

To make my multiscale basses I made a jig like the one shown by Jeremy Fullerton on the ANZLF. It works very well.

http://www.anzlf.com/viewtopic.php?f=24&t=2094

BTW, putting the perpendicular fret at the 12th will give you a helluvan angle at the nut. Sheldon Dingwall's 5-string basses have a 3" difference but the perpendicular fret is still at the 7th.

[Jason Rodgers]

I had forgotten about that thread on the ANZLF. Thanks for that, Dave.

Right, with a 3" difference in scale lengths, putting the neutral fret at the 12th is probably not a good idea. But maybe just fine for a 1" difference.

[Greg Martin]

I built my charlie hunter/novax style hybrid 8 string in 1998. The scales were 28.25 and 25.5.The nut and head stock were the tuffest part of the whole build.the compound angle for the trebles stopped the build for quite a while.i ended up fairing in the angle needed to keep the treble strings off the headstock, and gluing on a new thinner head veneer.
Do you remember at that time, Novax charged a licence fee to use is fanned fret system.long gone are those days.
novax told me he favored the perp fret to be the twelfth.i took his advise.if i ever did an acoustic version i believe the 7th or ninth fret would be perpendicular