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I gave up on routing fret slots after a few trys as it was way slower than the manual machine we already had. I'm starting to think about trying it again to take advantage of doing slots, inlay pockets and rough radius in one setup.

Anyone routing their slots?

Sheldon,
I too have mixed feelings about using a CNC Router to cut fret slots. I have had success using very shallow 1/3D passes along with a constant stream of compressed air to cool the bit and remove chips / dust. For the most part I cut my "normal" fret scales on the table saw and use the CNC for just fan frets and odd scale lengths that I don't have templates for the table saw jig.

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tim...
http://www.mcknightguitars.com

I use a .024 end mill and run at 24000 rpm @ 3 ipm. I cut them on a radius to match the fingerboard radius. It takes a little time, but I usually just let the machine run while I do something else. It's like having a non-paid helper....(well, now that it's paid off!).

I'll inlay first, leaving about .050" of wood right at the fret slot (.025 per side of the slot) if I'm doing a complicated multi-piece inlay. Then I'll radius the fingerboard, then slot it, then profile it. I never take the fingerboard off the table the whole time. This way, if I need to open a cavity up a couple thou, I just rerun the code to "tweak" the fingerboard cuts.

Trev

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http://www.PeakeGuitars.com

I just did one using an .023 end mill from Precise bits. .020 pass depth at 10 ipm feed and plunge rate. Router set at full with no extra cooling precautions (this was the second one I've done and no broken bits - knock wood). I then switched to an .03125 bit for the inlay. Everything (faux binding with a purfling strip, a 10" to 20" compound radius, fretting, inlay and the final cutout) done in one session. I put up a pic when I find the camera.

Bob

Fret slotting bits fail on beam strength, so you need to watch out for shock loads and overloading. The first is a matter of having smooth tool motion in terms for the machine and the toolpath, and you can take care of the second by being careful with your cut depths and chip clearance. Dust made by those cutters can pack in so densely behind the cutter that the stress increases dramatically on all depth cuts after the first.

With the right strategies, you can slot a 24 fret board in under 1:04 and get 50 boards to the cutter.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I use a .022" - two flute cutter on maple and a .023" two flute cutter on coco and ebony....both at 10 ipm and 4000 rpm with a .01" step down.

My first cut is with a .04" ball mill at a .02" depth to establish a small chamfer on the groove edges. The rest of the cuts use the above parameters. I follow the fretboard contour when establishing the depths. Grooves are .02" deeper than the tang to allow for sanding.

Keep the groove clear, like Bob says...most important thing, imo.

My cutters are particularly fragile. Having only a .05" cutting depth, I have them milled up the shank to allow the cutter to reach a depth of .1". I've only ever broken one by pushing it past the above parameters for a while. I'm probably near my 30th fretboard on the current bit.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

With the right strategies, and the right machine....! I wouldn't attempt anything near this speed with a router based machine. The runout on the routers is too high to allow higher feed rates IMO. I do 2 passes, each at .035 deep. I also typically chase the slots with a fret slot saw to make sure I have adequate depth after sanding, etc.

Doing a 24 fret board in around a minute is flying! That pretty much eliminates any need for a right angle head & a fret slotting saw I guess, eh?? Nice work Bob!

Trev

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http://www.PeakeGuitars.com

Unfathomable to get that done in a hair over a minute. That's blazing fast. I can't imagine a bit holding up to that, but I guess it must be possible! Not with my rig.
I'm with Trev about just letting it do its thing and doing something else. I rarely have to deal with dust in the grooves unless it's an especially oily wood.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

I run a .028" 2-flute carbide in ebony at 24KRPM and 20.0 IPM making three passes plus two full-depth cleanout passes. The ebony shavings pack in like glue as Bob alludes to above. Even then I find a cleanout saw necessary to get all the ebony dust out of the slots. I made a simple trunnion vacumn fixture that tilts a couple degrees each way for doing inlay cavities for .060 MOP either side of centerline. Also mill the fretboard perimeter as the last operation.
I do the radius by hand after the fretboard is glued to the neck. Rough it out on an edge sander with coarse grit and then finish by hand with a radius board.
Use to use a swing fixture on the edge sander but it's too slow, much easier to rough by hand.
Nelson

Nelson, I think if you were to get used to doing the radius with the cnc, you would find the results to be superior to doing them by hand, and a heck of a lot faster. I can't begin to tell you how many FB's I've wrecked using my edge sander and LMI style rig. Plus, then once it has the radius on it, you can do the blind fret slots with the radius as well. There really is something to them. They give you more meat under the slot, making the FB stiffer, which in turns also helps to hold the frets in better. Radius, slot, cut the perimeter, glue it on and fret.
For keeping the nasty stuff out of the slots, I use compressed air rather than vacuum.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

Hehe....maybe Bob meant an hour and four minutes?

I would add that for those who experience ebony chips packing in like glue....it could be because you aren't making chips...but making dust instead. An exercise in logic says that a jar of ebony dust would be easier to process into glue than a jar of ebony chips.

Feeding 10 ipm at 24K rpm with a 2 flute cutter shaves off a chip that's only .000208" thick....which surely crumbles as it's being cut or as it travels away from the flute. Slowing down the rpm will make a larger chip...instead of dust. My 4000 rpm makes a chip that's .00125"...more than 5 times the size of a chip made in the above scenario. When I cut fret grooves I can see chips coming off the machine.

I'm not certain this explains why I've never had my flimsy tools break from chips compacting....but I think it does.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

That would have been my guess... lol but if that were the case, it would be pretty achievable.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

yep, low feed per teeth = longer lasting tools, for sure...! (especially for those of us in the high runout club)

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http://www.PeakeGuitars.com

No guessing necessary.

24 frets at an average 2" length is 48".

Feed rate at 48 ipm taking the entire depth of the slot at once?

Bob's talking about an hour here.....which is about as long as it takes me to cut a set of fret slots.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Some good feedback here.

Bob, what size cutter, DOC and feedrate are you using? I seem to remember you using an air spindle.

Stuart, what DOC are you using?

A minute seems pretty fast but an hour seems way too slow. I looked up an old file and was cutting a bass fingerboard in 13 minutes.

Almost always .01" but if I want to push it I'll go up to .02" in maple. In ebony or coco .02" doc would prolly snap the tool at 4000 rpm.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

So using your specs of .00125" CL and a 65K RPM the feedrate would be 162.5"/min. I'm going to assume a .070" final depth so 7 passes x 48" @162.5"/min = 2.07 min plus ramping and rapids from slot to slot. That's not bad.

Carbide cost is higher than a blade. We probably get 600+ necks out of a blade.

Yep, all the production shops I've ever seen use blades of some sort or another. PRS has a gang saw for each scale length - it truly takes about a minute to cut those boards...! I believe Taylor has a right angle head with a slotting saw.

Trev

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http://www.PeakeGuitars.com

Re: dust getting packed into cuts, I've been lucky as it's never happened to me - although I've only cut two fretboards. I make four passed to get to a final depth of .08, but I machine the radius into the board first. Since my CAM will only give me 2D toolpaths for slots, only two passes wind up being a full .020 deep cut across the entire width of the slot. Maybe that helps... Either way, lots of good info in this tread.

Bob

I'm just waiting on someone to invent a gangsaw for fanned-frets

I meant 64 seconds.

90K spindle, feed is over 100IPM, and the toolpath has to be drawn by hand in CAD as no CAM software I've seen will generate it.

It was an optimized for production path, which I do manually. The entire boards, from rough blanks, with dots, radius, taper, slots, white binding, and black side dots took just under 7 minutes apiece in batches with no operation overlap. I don't think I could sustain that speed for full days, but 10 minutes each is doable.

If guitar companies were as willing to pay for better manufacturing strategies as other industries are...

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Very cool Bob, that's hauling. Assuming a 3 flute cutter the CL would be .0004". Is that correct? What were the pass depths? Precise bits recommends full depth cuts which is what we were doing but we had packing problems.

Bob,

Don't take offense......... my two cents.......

In the short distances and if you take into consideration Ram-up and Ram-down............ I don't think your machine will cut at your 100IPM fret slots.......... don't doubt your time........

I typically set my files for instruments at 800ipm or 1200ipm knowing that my machine will never reach anywhere close to this speed given the confined area. It takes me 4.45 min to radius a standard dread style fret board using a 3/4" roundover and 8% stepover set at 1200 IPM with a 16" radius ( machine never reaches anywhere close to this speed ..... it might if we where to use more of the table given our y axis is 12' but not on short contained areas ) by the way the fret board given this setup doesn't have to be sanded further at this point. We use a laser to cut fret slots and dots.......... it takes 2.4 min to run 21 frets and 10 - 6mm dots.

Side Note:
We don't think that the effort for making fret boards for the public is worth the profit margin given the time, handling and manpower necessary. Even though it doesn't take long you still have to line them up on some kind of fixture....... vacuum etc. an in our case two different machines......... We only have one head on the cnc and one head on the laser ............ this kind of business is better served with multi-head set-ups.

Kevin

At full accel, it hits 100IPM in a little under 0.03" and 200IPM in under 0.125". A moving table machine can handle some pretty high accelerations compared to a gantry machine. The control and power electronics on my machine are modified pretty heavily, so those numbers aren't in the range on a stock DC motor Fadal for sure.

It's been my experience that shallower passes work better than the full plunge they recommend. When the cutters break, the majority of them fail at a direction change or the beginning of lateral movement after the plunge. T&T do give good advice, though, so I'm sure it works alright with whatever their machine parameters are.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Bob - I didn't think you'd mention your time if you were talking an hour or more to cut fret slots!

Kevin - slick use of the laser to cut fret slots. That's a new one to me, but that's a cool idea

I have a friend at work who designs & builds benchtop CNC's (he's a tool & die guy by trade). One day I'll have him make a custom fret slotting setup for me with a slotting saw (assuming I build more than a handful of guitars per year at some point). I have yet to snap a slotting saw....

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http://www.PeakeGuitars.com