Official Luthiers Forum!

I run a cnc machine designed for woodworking and it has a grooving saw within the drill head, what i have done in my workshop is to have a saw blade manufactured with the last 10mm of the blade bossed down to 0.58mm, the blade is 120mm dia and it has 100 teeth on it simular to the one you can buy at stews.

I thought i would let you all know how i do it in my workshop.

Jeremy....

Interesting thread. I am now a CNC owner and one of the first things I want to try is a f/b. This is such a new tool for me, and I'm starting with very limited knowledge. Seems everything I read or review raises more questions! I got a f/b drawn up yesterday in Rhino and modeled the slot at the 0.023 cutter diameter but was wondering if I could have just modeled a line at the appropriate depth and saved some time.

Ken

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http://www.casperguitar.com

Use a line, it makes things easier for both the slotting and the radiusing in CAM. Quite a few CAM packages won't follow a line as a toolpath, though, so you might be stuck modeling it as a pocket of some sort if you're using one of those.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Thanks Bob. I use RhinoCAM. I will have to look into whether that package is one of 'those'.

Ken

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http://www.casperguitar.com

I use madCAM with Rhino, and do fret slots as Bob suggests--just lines. I lay out my fret positions on the Z0 plane and use a "project curves" toolpath to put the fretslots onto my fingerboard model, and it works great. I set up the fret slot depth as an offset distance in madCAM, and I get fret slots that are a consistent depth and parallel to the surface of the fingerboard regardless of radius just like you'd want. I think you can do the same thing with RhinoCAM, but I'm not sure.

Dave

Thanks Dave. I had made rectangles the width of the fret slots and projected those to the radiused surface, then extended them down the proper depth and removed the solid. The drawing part isn't bad as I own illustrator and just need to learn the 3D. But CAM...well...that is entirely new, so don't have much of a feel for it yet. I may have to work through a few tutorials.

Ken

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http://www.casperguitar.com

I'd have to double check but I'm pretty sure you can use the engrave function to do curved slots with multiple passes in VisualMill/RhinoCam

I tried that too, but it was quite a bit more work--just to clarify, the "project curves" that I used with madCAM is actually the madCAM toolpath function and not the Rhino project curves. I think that Sheldon is right about the engrave toolpath in RhinoCAM being about the same thing as the madCAM project curves....

Dave

I use VM for Solidworks....which is the same as RhinoCAM and that's exactly the best way to do it. Engrave is under 2.5D but it is actually a 3D tool path.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Following a curve is also a good way to do a really custom toolpath, if you ever have the need. There are a few parts where drawing out the exact tool motion I needed saved a lot of time VS any CAM generated path.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I've done virtually all of my programming using either polylines or digitized point clouds.
Have done a little with 3D CAM using trial versions but don't own any 3D CAM.
It's fairly easy to offset some lines for cutter comp once the part is drawn in CAD and it gives the programmer some "manual flexibility".
With that said, I am in the market for 3D CAM.

I use Solidworks and MastrerCam X5.

When doing fret slots I generate an offset surface .08" below the fretboard surface. Using a contour toolpath that follows the middle of the fret line, I project a series of paths onto the offset surface leaving .07", .06", .05...ect. ....until finally .00".

The first two depths are made with a .04" ball mill and all subsequent depths are done with a .023" endmill.

The net result is a total depth of .08" with a .02" chamfer on the slot....and this assumes up to .01" of material for sanding and a slot depth of .07"...though I doubt I ever come anywhere near sanding off .01".

I'm thinking REAL hard about getting a spindle multiplier. I'm limited to 4000 rpm with this machine and the slots take 45 minutes per board....which is ok for a one man shop...but still. I cut the slots of 16 fretboards the other day....putting the total number of fretborads cut on this bit to over 60....so there's doubtless, some room to advance the feed rate.

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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

Yes, almost certainly!

I'm running my spindle at 18k and cut about .030-ish per pass at 20ipm. Takes about 7 min or so. That might be a bit aggressive though as I broke my first bit the other day after about a dozen or so boards.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

I take the full depth of the slot in two passes running about 24K and 25IPM with .028 EM.
Then take a couple "air passes" to clear the ebony shavings out of the slot.

Once I get my two current builds done, a fretboard will be my first CNC challenge! And I did figure out how to do lines using engrave.

Ken

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http://www.casperguitar.com

I picked up one of these: http://www.mcmaster.com/#catalog/118/2727/=h0txe8 single hose nozzles and blow as I'm cutting.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

I forgot to share this the other day.

On a hunch I tested an idea I had based on Bernoulli's principle...which states that the faster you accelerate a body of air...the less pressure it has. This is how airplanes fly.

The idea was that if I positioned the air nozzle to blow horizontally over the top of a fret groove while cutting, the chips will pull up out of the groove and into the stream due to the pressure differential.

I positioned the nozzle to blow just behind the cutter and I only cut from one direction.....It worked!

I cut 16 fretboards and never saw any residual or compacted chips in the cut grooves.

The plus and minus symbols in the illustration indcate air pressure differential...the chips are sucked out of the groove....and blown clear so they don't get compacted

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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's really cool, Zlurgh. I'll have to give it a shot--I haven't had a problem with the chips compacting, but it's been due to a lot of hand vacuum work in addition to my usual dust collection setup. This would be a lot easier, and it makes good sense.

Dave

same principle as a siphon venturi in an airstream. the high pressure stream draws air from the low pressure siphon tube that is in the path. Same as used in spray guns.

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I'm outside looking in, just farther from the window than most.

That's a really cool idea. Thanks for sharing.

What's your thinking behind only cutting in one direction?

Stops the cutter from getting between the air blast and the chips.

Stuart:

So far as getting a speeder for using small cutters, I'd look into getting a small spindle from Keling or someplace like that. The gearing on speeders tends to wear over time unless they're very expensive, and any I've seen with a decent reputation have been more expensive than a cheap spindle.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I also cut in one direction but my thought was that if the cutter is deflecting, it would be in the same direction each pass. I go for 3 passes per slot as it's too difficult to make a custom "no jerk" tool path that automatically updates with changes to the model.

I don't know Bob's secret sauce exactly but if I'm guessing correctly, it would take a bi directional path as far as I can figure.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

It works better in one direction because the chips always get ejected from the trailing side cutter. If the the airflow is focused right behind the cutter, instead of blowing straight AT the cutter then the airflow remains laminar...or basically...in an uninterupted line. This means the airflow has the highest velocity....and the highest potential pressure differential and will, therefore, make the highest amount of vacuum over the groove.

This may not work in every application. My chips are pretty small because I take little depth bites due to low rpm on the spindle. More aggressive chip loads might result in bigger chips that will not pull out as easiliy....idk.

If you try this.....the idea is to get an airflow going as fast, as horizontal, and as close as possible above the surface and to the tool without ACTUALLY being obstructed by anything.

And yes....blowing the from the cut groove direction to the uncut direction will result in chips not accumulating in previously cut grooves.

Anyway....don't have super high expectations....I can see a number of variables here.

Bernoulli....he's the man.

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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

I thougt that very thing....that a small armature on two bearings would be infinitely better than a gearbox for durability. If it weren't true...Haas wouldn't have made their direct drive spindles.

But I couldn't find anything that would mount in a cat40 spindle....not that you have to mount in the spindle but that sure simplifies things.

Is there such a thing? A cat40 mounted spindle motor?

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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

http://www.artcotools.com/air-turbine-s ... 16946.html

Kinda pricy though.

_________________
http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com