Official Luthiers Forum!

Hi Dave, I realize this post is from months ago but I'm so happy to see a fellow Rhino / Grasshopper / MadCAM user here!

Love the 7-string bridge test-cut. Any more progress photos?


I got into Grasshopper because I was getting tired of constantly importing multi-scale fretboard geometry from the FretFind2D website. So I got a fretboard generator working in Grasshopper about 9 years ago and couldn't stop... now my Grasshopper definition has many thousands of components and generates the whole solid body electric guitar or bass according to my length list of specs.

It also generates the cutting layout for each part and some of the simpler Gcode cuts directly. The rest of the Gcode is generated by madCAM automated by Rhinoscripts.

Amusingly, I've been spending so much time programming and building CNC machines that I've yet to complete a single instrument with this elaborate CNC-based production process. Keeps me out of trouble though!

Last winter I actually cut my first part:

It's a tiny brass string roller wheel which fits over two 3mm x 1mm bearings on a 1mm stainless axle. (My index finger for scale.) This is for my adjustable nut design. I don't have a lathe so I tried CNC mill-turning and it worked beautifully after a few months of brain-mashing visualization and Grasshopper coding.

When I went to cut the next parts which are a pair of nested brass brackets which capture the axle and provide adjustability for action and intonation I realized that each part needed to be clamped in 5 different cutting orientations. Trying to do this on a 3-axis mill seemed like a fools errand so I set about adding 5-axis functionality to my tiny CNC mill.


Having rewired the whole system with UCCNC motion control and CNC-Room breakout boards I achieved good calibrated motion on all 5 axes and then thought "Well with this much complexity it's time I built a proper CNC control panel with a manual pulse generator wheel."

My quick & dirty prototype control panel:


Which brings me to today where I am wiring up said control panel.


Fun times! I fear that if I don't actually build a guitar soon I may cross the line into complete insanity but in the meantime my inborn stubbornness is keeping me going...


So if Dave or anyone else wants to chat about Rhino, Grasshopper, CNC etc. please feel free to message me
Leo

Your pics aren't showing. If possible, scale them to reasonable size and upload directly to the forum rather than linking to google. That way they will remain viewable for as long as the forum exists, rather than disappearing into the void whenever google changes their URL format.

I'd love to see what your 5-axis setup looks like. I'm not sure if I could use such a machine if I had it Too poor for CAM software, so I write C++ programs to generate gcode in a slightly more user-friendly way than writing gcode directly. I do want to add a 4th axis, but tying to visualize 5 axis tool paths might be too much

I ended up declining to work on this guitar but thought I’d post some pics because it had some of the wildest ornamentation I’ve seen.






It came in because the guy who commissioned it was disappointed in the sound and wanted to know if it could be improved. It was ordered as a nylon string guitar but looking inside I saw it was extremely overbraced. Torres style bracing layout but the fan braces were 1/2” tall and 1/4” wide!

Nice carvings though.

So what happened to "our top notch quality sounding guitars" - bracing like that?

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Looking online at other instruments from this maker it sure looks like visual bling is a major (perhaps the major?) design consideration.

Just Finished

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Never met a STRONG person who had an EASY past !
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Nice ductwork Wud. The guitar looks good too

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Steve Smith
"Music is what feelings sound like"

Holy crap, Josh! Whoever did the ornamentation on that classical overdid themselves. What a showpiece! Too bad it's braced like a battleship.

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"Act your age, not your shoe size" - Prince

Killer guitar Wud, very well done my friend.

These have been around for a while and are imports that are marketed in North America by someone other than the maker. We've turned away two because they were not well constructed and that's why we had them brought to us things went wrong.

They have a loyal following though and some of the owners tend to collect multiples of these. I have a friend who's sister has three of these....

Thanks Dennis, I've shrunk the pictures and they seem to show correctly now.

The 5-axis setup is on my tiny mill. The rotary axes use steppers and 100:1 strain-wave or harmonic-drive gearing with impressively low backlash.

I'll also be generating the G-code myself using the Python component inside of Grasshopper. Fortunately I don't need any fancy 5-axis simultaneous motion, just simple 3-axis cuts but from 5 different sides of the workpiece. Figuring out how to calculate those positions will be an interesting challenge.

Beautiful guitar!

And yeah your shop is equally impressive!

Still no go for me... just small boxes of failure instead of huge ones:

I love strain wave gears. I want to try making itty bitty ones for guitar tuners, but I'm not sure if it's actually possible. With a 0.5mm bit I can mill 24 teeth into a 3/8" steel rod for the flexspline/tuner post, but due to their relatively large size it will need to flex quite a lot between full engagement and moving past ring teeth. Also due to their relatively large size, all that flexing will be concentrated into the 24 short spans of metal between teeth, and probably fatigue it.

I could reduce the height of the teeth so it doesn't have to flex as much, but then the tolerances become even tighter to prevent skipping. Ideal would be to reduce the width of the flexspline teeth to leave wider flexible spans between them, but then the ring teeth need smaller spaces between them and I can't mill that. I could also try going down to 0.3mm end mill, but then tooth face width is limited to 1.5mm (even less after deburring) and that's pretty tiny for guitar string tension even with multiple teeth engaged.

Yeah, that would be much easier just using it to reduce workholding changes. Although figuring out how to hold onto the raw stock in such a way that you can get at 5 sides doesn't sound so easy either... and then how to machine off the portion that was being held.

In my 3-axis programming, I have a variable to rotate the entire coordinate system around the Z axis. Ultimately, all movement is done via functions like G01_XY(x, y, feedrate), which will rotate those coordinates, apply backlash compensation, and then write the G01 command to the output file. So for example I can write a tool path to cut one gear tooth, and then use a loop like for(int tooth = 0; tooth < toothCount; tooth++){ setRotation(tooth*360.0/toothCount); cutTooth(); }

You could probably do something similar for your 5 axis system, where your programs are written in XYZ space, and all the transformations to 5 axis are done "under the hood".

Try using a free photo hosting site like IMGUR....

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"Act your age, not your shoe size" - Prince

Dentellones, tentalones, peones, blocks. whatever you like to call them.

Thanks Chris. Just switched hosts from Google to postimage.

Hopefully that works.

Dennis that would be amazing if you make a strain-wave tuning machine!

I'm also fascinated with them. I thought I had seen something on the internet years ago of Frank Ford making some banjo tuners with the same gearing. Searching just now I could only find a video of him having made a cycloidal geared bass banjo tuner set:

https://www.facebook.com/watch/?v=1035108589962772

Edit: found a link to the banjo tuners I was trying to remember. They're cycloidal and you can see the gearing mechanism is just behind the tuning post. Frank Ford helped develop these.
https://rickardbanjos.ca/collections/hardware/products/rickard-10-1-high-ratio-tuners?variant=38057221750966


One thought regarding your design: could you put the mechanism in the tuning knob instead of the tuner shaft? Like a Steinberger gearless tuner? Might give you a significantly larger diameter to work within than the shaft.

Another question for you, what type of mill do you have that you can cut with such tiny cutters? Do you have a high RPM spindle?

Love to see updates on this if you do any tests

Success at last! Your machine looks great Larger than mine at least, which has a work area of 175x150x111mm (wish I would have given it another 50-100mm of Z range). The exceptional feature of mine is that it only weighs 35lbs. I don't have room for stationary tools, so everything has to be light enough that I can move it to and from the bench easily. These photos are from various stages of its development, so you can see some features being added over time




My spindle is not very fast. About 4500RPM at the moment, though I could change to a 24V power supply to double that. I'm using an old computer supply. Just have to go slow with the tiny bits.

I have seen those cycloidal tuners. That is my favorite reducer mechanism of all But despite its reputation, it's not inherently zero-backlash, and I don't have the precision grinding ability to make it so. Plus I think Rickard has been granted a patent on the use of it in guitar tuners (which seems rather ridiculous to me since it's such an old mechanism). Hopefully Harmonic Drive's patents on strain wave gearing don't apply to use in guitar tuners, so I can establish the prior art on that and make it free for everyone to use.

I have made some pretty small cycloidals for another project. I think this disc is aluminum. I first made them in titanium, but due to a machining error in the ring/housing (my mill was out of alignment) they were jamming, so I had to make some with a bit more clearance and save the titanium discs for the next copy of the part with the ring.

The best procedure I've come up with for machining gear-like things is to first do all interior holes, then add workholding in the middle, cut a circle around the outside with a big tough bit, and then start working the curvy profile with the small bit. Nibble into the spaces between teeth using vertical motion, taking small enough bites that the center of the bit remains over open space. Then do one rough profile pass, and one finish pass. That way the small bit never takes a heavy side load, and you get excellent chip clearing (I use watered down Anchorlube for coolant, and apply enough that all work with the small bit is done submerged in the pool).

The knob will be axial like Steinberger or the cycloidal tuners, rather than 90 degree like worm gears, but I don't think I can put the mechanism entirely inside the knob. If you turn the ring gear as the input you get speed increase rather than speed reduction.

I'd like to have them interchangeable with standard tuners, with the ring gear being mounted to the back of the headstock, and the toothless portion of the flexspline cup fitting inside a 10mm hole in the headstock, stepping down to a 6mm solid post for the string. I don't think I can fit a housing around the outside of the flexspline cup, so it will be naked in there, with nothing to screw a grommet into. So it will need press fit bushings to support the posts like open gear tuners.

Wow! Your DIY machine is impressive and inspiring!

I’m amazed that you’re able to cut such tiny parts.
I’m a complete beginner at machining and my spindle is about the same speed as yours so I really appreciate your sharing your cutting strategies.

I’m sure I’ll be breaking some of my small bits but probably fewer by following your style.


I hope you’ll post more of your tuner development. Super interesting stuff!

My way too patient friend asked if he could pick this up in two weeks after waiting three years. I’m finally on the last haul. The body is ready to buff, but the neck needs a little finish touch up before buffing and fretting.


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Love the crisp, understated aesthetic. Beautiful.


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Beautiful James, looks like a great guitar soon to be.

Here is my first go at an archtop. It’s based on an L-5, has a 16” lower bout, 25” scale, is a 15 fret, and is Sitka over maple.

Gorgeous, Michael!


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Thanks, guys!


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