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demonx

Fingerboard slots on CNC

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I've bought the end mills and have a bit of an idea, but before I go breaking any in trials I thought I'd ask how others are going about using these half millimeter bits successfully?

How deep pass? 0.25mm? What's an average without breaking?

How slow feed speed?

Drill or ramp? I can see both methods would put different strain on such a fine bit, the ramp would flex it, but then the drill would apply pressure when the x or y movement begins

Curious to hear your experiences. Thanks.

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First thing, be aware with that narrow of a bit, you'll get into trouble trying to seat any normal-sized frets. I learned that even for frets with a .021" tang, a .023" bit is iffy unless you're using softer woods. I ended up with a neck that had so much back-bow that it looked like the St. Louis Arch.

Depending on the type of wood, I ramp at about 15-30 in/min, taking .025" per pass. As with everything, start conservatively and you should be fine.

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First thing, be aware with that narrow of a bit, you'll get into trouble trying to seat any normal-sized frets. I learned that even for frets with a .021" tang, a .023" bit is iffy unless you're using softer woods.

The endmills I've purchased are .56mm, which is virtually the same size as the stew Mac saw blade I've been using for the last couple years (.58mm) and the same size as the stewmac fretsaw that is now as blunt as a butter knife.

The fretwire I use has a tang width of .508mm and I've never had an issue with frets being too tight. Im also going to make the assumption that slotting with the endmill with several passes won't br exactly .56mm and it'll be very close to the .58mm anyway.

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Depending on the type of wood, I ramp at about 15-30 in/min, taking .025" per pass. As with everything, start conservatively and you should be fine.

Out of curiosity, have you broken many bits?

Your ramp speed is a touch faster than I was planning, you're around 380mm and I was thinking of going around 300mm to play it safe, but your depth of cut surprises me

I've been led to believe that it's best to try cut no deeper than half the router bits width,you're cutting at its full width, which in guessing would put a lot of stress on such a small bit.

Like I said in the op, I haven't used these small bits yet, Im just painting a picture in my head before I do. I know that Ive broke enough of the tiny stewmac bits in my dremel to have given up using them, so I want to play it safe on the cnc!

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I used to use the StewMac thin kerf table saw blade, which was advertised as .023" (.58mm). That worked fine, which is why I started with the .023" endmill. They definitely didn't give similarly wide slots. The wobble of the blade and the tighter tolerances of the endmill combined to make much smaller slots on the CNC.

I've taken .030" passes with a .023" endmill in ebony (remember, this is a ramping op, so that max depth of cut (DOC) is only at the very end of the path), but that's as far as I'm willing to push it. It's really not as bad as it sounds, it comes out to 0.00075" per tooth (normally I shoot for .001"/tooth on bigger bits).

I broke two bits while I was figuring out what speed/feed rates worked best. They're cheap, so I wasn't too upset; besides, education is worth the price :)

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Interesting, I thought the spinning bit would have the opposite effect.

What is the tang width on the wire you're using as that could make all the difference?

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I've been using the stainless wire from Allied lately, so .019" or .021" (the barbs measure .031" and .037" respectively).

If you're trying to shove a .021" tang with a .037" barb into a .022" slot in ebony, you're gonna have a bad time ;)

Some advice I wish I were given when starting out w/ the CNC: Tight tolerances are good, but a "perfect fit" needs a bit of room.

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I'm glad I asked, as the tangs you're using are wider than mine, not heaps wider, but enough to make just make that bit of difference.

I'll still run some test cuts to be safe though. I've stumbled across something else that is a bigger priority to work out at the moment so the fret slots will be on hold for a week. Turns out the jigs I made to do the neck wont work how I planned, so I have to rethink and make them again. I allowed for the scarf joint angle etc, but I didn't allow for the crease to be in a different place when I flip the neck, in that error, it also creates other issues with varying depth of neck blank with different heel angles etc, so I need to come up with a new plan to flip the neck on the bench.

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As with everything, ymmv. This is just my experience, and what I've found to work for me.

I'm curious how you're doing scarf joints on the cnc. Are you actually cutting the scarf on the machine, or is the scarfed headstock glued up beforehand?

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I'm curious how you're doing scarf joints on the cnc. Are you actually cutting the scarf on the machine, or is the scarfed headstock glued up beforehand?

Making the blank beforehand as per usual to put under the CNC.

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If you're not planning on making blind fret slots, cut them on the CNC and then open them out with a saw. Sounds like it is defeating the object, but nonetheless maintains the accuracy of CNC.

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If you're not planning on making blind fret slots, cut them on the CNC and then open them out with a saw. Sounds like it is defeating the object, but nonetheless maintains the accuracy of CNC.

Being that I can fret an entire board accurately with my slotting jig in around a minute, the only reason I'd be even looking at doing it on the CNC is for blind slots as you call them, where the slot doesn't break out the side of the board and the ends aren't visable, or down the track for fanned frets.

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That's what I figured. Other than basic "suck and it and see" the slots probably shouldn't be milled as slots. DC Ross is on the money I think. Good to hear you sharing progress and experience within the learning curve.

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Uhhhh.... @DC Ross, where are you getting "cheap" fret slot cutters? I'm learning and just snapped one and kissed $20 (precisebits) goodbye! I'm not seeing them any cheaper on places like HarveyTool.com either.

This may be the most frustrating CNC learning step yet...

Chris

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Ha, yeah, the PreciseBits are the cheap ones. Well, cheaper than the $80 1/2" spiral bits that I use for most ops that I need to replace every 6 months :)

I haven't broken a slotting bit in quite a while, using those numbers I quoted above. What are your feed, speed, and depth of cut?

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I was going at .3333in/sec and .030" DOC. I think the issue was trying to get MeshCAM to actually do this radiused slot operation... which I'm having a heck of a time trying to make it do... seems to be the only limitation I've found with this 3D CAM package so far. There's no "follow this line in 3D" function. So I've have to model the slots in full 3D... and it still just isn't grasping the concept...

Granted, I also haven't played with ramping at all... should probably learn a bit about that.

Chris

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You might find it easier to manually edit the NC file to make each slot follow a radius. Should be fairly easy to identify each linear slot and convert it to an arc around the Y axis.

0.33" per sec is 20" per min. Maybe that's asking a bit much for some bits? I've done 3 boards with a 0.023" twin flute Kyocera bit (eBay in packs of 10, not expensive), 12"/min, ramping to 0.012" at each end of the slot without any issues. Could probably go harder with experimentation, but haven't tried it yet.

I would think that making a direct plunge into material to a depth of 0.03" and suddenly wrenching the bit sideways to begin the slotting operation would be asking for trouble with small bits, even at low feedrates. The gentler approach of ramping into the cut is ideal for this kind of work.

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Sorry I can't help with your MeshCAM issues, but I'd be surprised if there's no "Groove" or "Slot" operation that allows you to choose a 3D path for it to follow...

I've modified my approach somewhat since that post from Dec. 2014. I now use a 2-flute .027" diameter (.025" for non-ebony) carbide bit, at 20,000 rpm, going 30IPM, and cutting .01" deep passes, and it poses no problems at all. 

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