Official Luthiers Forum!

I teach a mech engr senior design class and we're currently looking at project ideas for feasibility. It seems that there is currently no commercial CNC machine that is optimized for guitar luthier use, at a low to modest price. What level of interest do you think such a machine would have? I'm thinking of some customer requirements like these and welcome any feedback on what you would like to see.
- Precise enough to do fine inlay, so repeatability of 0.001" or so, reasonably good stiffness, no axis slop.
- XYZ travels of around 24", 18", 6". The 18" could do archtops (?) and insides of molds. More travel is always nice, but it makes it harder to achieve good repeatability, and of course the machine is larger.
- Construction material is unclear. Could be aluminum, steel, MDF, BB Ply, Marine ply, or some combination. Each has pros/cons.
- Turn-key retail price... unclear. Where do you think the best market is for this kind of machine?

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David Malicky

Here's a good example of a luthier style CNC, it's large enough to do a neckthrough bass if desired, has vaccum capability for luthier fixtures. Extremely sturdy construction.

http://www.luthiertool.com/cnc_linear.html

It's accuracy is only .005 though.

Altogether it's 15 grand.

There's a starting point for consideration...

There's also the Chinese machines about $6000 shipped:

http://www.ebay.com/itm/CW-6090A-CNC-Ro ... 232e57e4bd

If you can do better than this, you'll probably find a market

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Old growth, shmold growth!

He's probably being very modest. With the components he's using it should be possible to tune it down to .001.

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

Wouldn't surprise me at all, I've purchased a few things from him, and they've all been even better than they look on his site.

He has no control over the capabilities of the end user and likely doesn't want to oversell.

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Old growth, shmold growth!

Thanks for the replies. It's hard to know what is meant by "accuracy"... linear, planar, volumetric, and over what part size. Volumetric is pretty hard to measure. For this class machine, I'd consider 0.005" linear accuracy over 60" to be plenty good... e.g., just a 10F ballscrew temp rise will lengthen that axis about 0.004". Short length accuracy will be much better. Fortunately, luthiers need repeatability much more than accuracy.

Any other thoughts on specs or price for a luthier CNC?

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David Malicky

Something I just noticed - You actually want a work area a bit larger than 24x18 and the 6" Z travel might be a little short if you want to carve acoustic necks etc.

The work area should be the size of your largest stock + 1/2 diameter of your largest endmill + a little bit of slop. If you want to cut 24" stock, you should probably have a travel of at least 26" to be on the safe side.

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

I'd think the smallest footprint possible to be best. Most of us have small shops. Mine is about 800 sqft. I know to some this seems enormous. Still... My current CNC is about 22"x 36" overall with a capacity of about 24"x 12"x 4". Not big enough or stiff enough to carve a neck.

Andy and Michael, thanks for the replies and info. Students picked other projects for this year, but I'll work on this on my own as I love designing machines.

Andy, on Z travel, I was thinking the router could be mounted higher to accomodate a long tool for heels. The disad of more Z travel is more carriage mass and a higher CG of that mass, which tends to cause vibration. How much Z travel do you think is needed to not remount the router? For X&Y travel, jumbos would need 19" x 23", an 18" archtop a bit bigger, but both of those are small markets. To do the outside of molds would add 6" to each axis; I'm thinking that isn't worth it, and makes the machine much bigger.

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David Malicky

You need twice the height of the tallest part you will machine, plus the height of the fixture you use to hold it, plus 1/2" of Z height at a minimum.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Thanks, Bob, very logical. I've only done electric necks so far, so haven't faced many Z travel issues.
So, tallest point of neck carving: 3/4" spoilboard, 3.75" heel, 3.75" tool length, +1/2" = 8.75" from table to collet. (Assumes a tool of ~just the right length.)
For lowest point of body profile: 1/2" spoilboard, 1.5" tool length = 2.0" from table to collet.
For lowest point of inlay: 1/2" spoilboard, 3/4" tool length = 1.25"

Net Z travel is a minimum of 6.75" or 7.5" without remounting the router. Inlay would likely be done with an air spindle, so maybe ~7" would do it?

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David Malicky

You could also machine the neck on its side, indexing off of the truss rod slot and a pin. This requires two set ups, a left and right but could be done in one fixture, even one program that incorporates a retract and pause if you so choose. This has the advantage of shorter Z, Shorter tools and you can have the undercut in the heel region, which appears much more elegant to me, vs a straight heel.

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Jim Watts
http://jameswattsguitars.com

Thats got the wheels turning!!

Great idea!

Thanks!

Jim I like this idea. Would you happen to have a picture of the fixture?

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Bob, unfortunately I have no picture.Here's a quick concept sketch though. Input more than welcome.

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Jim Watts
http://jameswattsguitars.com

Thanks, Jim, that is slick. I can't quite read the text in the sketch... are those 2 screws/pins at the end to clamp/locate the neck to the fixture? Then the other side is clamped? For the machine I'm designing, I'd like to make it suitable for any method so will aim for a 7" Z, but if that's not enough your method saves it.

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David Malicky

David, I don't machine necks, so this is a concept and the way I would approach it. I have successfully employed such strategies in the machining of many double sided components in the past however.
The holes on the end are for a locating pin, They match a corresponding hole in the neck and locate the neck along the length of the fixture. There are two holes to accommodate flipping the neck from one side to the other.
For clamping I would probably turn this into a vacuum fixture, but you could leave some excess material for clamping tabs if so desired.
Sorry you couldn't read the text, if you're interested I send you a file in pdf, jpeg or solidworks (or the usual interchange files) just lemme know.

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Jim Watts
http://jameswattsguitars.com

Are there any high quality but small/cheaper CNCs out there? Like just big enough to do a bridge?

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Pat

Hi Pat

I have a CNC Shark made by Nextwave Automation. It's the base modle unit. I have made a few upgrades.

I use it to make my bridges, fretboards, my headstock profile, rosettes, all of my inlay work, and I've made a bunch of tools with it as well. If you work around and understand its limitations, it's a great little maching! I gave $1500 for it used on CL. It's fully rebuildable in something goes wrong, and the folks at nextwave have been very quick to respond if I have a question or a problem.

PM me if you want to learn more about it...

Cheers, M

Hi Michael, Thanks, that is encouraging. What type of modification did you do? To increase rigidity and accuracy?

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Pat

Pat

I upgraded the table top using 80/20 1030 extruded aluminum ( 80/20.net ). I also added dust collection, and upgraded the router collet with parts from precisebits.com . Check out the luthier section at precisebits.

If you're ever in PT, I'd be happy to show you how it does.

M

what software are you using on the shark cnc???

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MK5acoustics.com

Jim, Thanks for the info, makes sense.

Pat, there's also the Microcarve http://www.microcarve.com/mcMV1.html. Recent discussion here: viewtopic.php?f=10101&t=41195

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David Malicky

The one I used for necks in production was similar, except it had a 'top' along with the two side fixtures. I used pins for indexing (both in the truss rod slot and elsewhere: much easier to drill holes rather than leaving a boss), and vacuum for hold-down. The brick of aluminum I made it from, plus the piece for the base, made it 'special' to move around...I think it weighs at least 40-50 lbs. It also had to be indexed, squared, and leveled perfectly, so putting it on the machine was a process.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services