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Very exciting Burton and Dennis!

I am also fascinated by cycloidal and strain-wave mechanisms and would love to make my own tuning machines some day. Here's a video comparing the two:

https://youtu.be/IXmCze1GsGU

Also as an aside I am deep into the Grasshopper/Rhino world and am building a definition to generate my entire parametric electric guitar/bass model including cutting files. Grasshopper is incredibly powerful.

How does a feller hold a patent on a type of gear mechanism invented by a German guy decades before his birth?!

Excuse me while I patent the worm gear and sue Grover into oblivion

Grasshopper is a lot of fun. I've used it mostly for fingerboards and archtop plates--does a reasonable job of emulating Solid Works (which I just can't afford). Works with my MadCAM layers too.

Dave

I've watched students use grasshopper and felt a little meh about it but seeing it used for purpose rather than just for loosely modulating things opened my eyes. I haven't dug into too much myself but it's on my list of things to practice when I have time.

It made me realize how poorly I learned math in school- I did well, and took AP classes, but I don't think I ever fully understood it as a whole system. It was just memorizing equations and implementing them in the correct places. Watching someone use CAD programs efficiently, and especially when using parametric tools, makes me want to dig back into basic geometry.

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Burton
http://www.legeytinstruments.com
Brookline, MA.

Sine and cosine are the keys to the universe Cosine is the x coordinate of a point on a unit circle, sine is the y coordinate. Amazing how much you can do with them.

I've been toying around with the strain wave teeth, and I may have a winner. First I scaled the height by half, so they're about 0.3mm tall. Then scaled horizontally and fiddled around the vertices to see how small I can get them while still being able to fit a 0.5mm circle between teeth. That resulted in 30 ring teeth (15:1 reduction). I also tried reducing it to 14:1 which allows stretching the space between flexspline teeth a little, to spread out the flexing and reduce fatigue. Not sure which I like better...

Only 3 teeth are actually adjusted here, and are still pretty rough. I'll clean one pair up and write out toolpaths for them and mill up some test pieces in aluminum to see if it seems worth trying in steel and brass.

Experimental strain wave #1 is not quite right, but does show promise.

Here's how I write the programs for milling the teeth.

The highlighted circles are tool positions. The big one is a 1/16" mill, used to cut a circle around the outside and then clear some material between teeth. The non-highlighted circles represent the radius for arc commands. After copy/pasting the positions of those circles, the C++ code looks like this:

And the resulting G-code looks about the same, just a lot of repetitions with the positions changed according to that rotation setting and backlash compensation.

Here's a shot of the machine in action. This is the 0.5mm end mill, using vertical motion to nibble away material between teeth before cutting the curvy profile. This approach never puts a heavy side load on the delicate little bit. This piece of aluminum has 3 holes in it and a failed gear from a previous project. But just enough material left in the middle for the 3 components of this project.

And here are the finished pieces. The ring gear's outside diameter is 1/2".

Note: The 4mm hole with keyway is just for testing, because I happen to have a corresponding shaft on hand from a previous project. For actual tuners I'll probably use a 5/32" shaft with 1/8" flats, for compatibility with standard closed gear tuner buttons.

The flexspline does not want to go into the ring gear, so I need to re-make it with a bit more clearance. And remake the wave generator because I accidentally doubled the x/y radius offsets, so it's much more eccentric than it should be. I was able to get it into the flexspline, but it deformed permanently. I also need to reduce the flexspline wall thickness even further (this one is 0.25mm). Even if the eccentricity was correct, it still feels too stiff. I think I'll try 0.2mm next time, but even that may not be thin enough, especially for steel.

Wow that’s impressively small and precise work!

Forgive me if you’ve already told us but what software are you using for modeling and motion control?

It's simply hand applied dye. Sorry to disappoint

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-Marcus
http://www.bailieguitars.com
Instagram | YouTube

Blender for modeling, but only for reference (no direct utilization of model data). Programs are written using my own C++ helper functions, but still pretty close to direct gcode. The CNC runs on a common GRBL board.

Well whatever, it looks great.

Got a couple of client OM’s strung up. They sound good to me. Pretty generic music machines. Rosewood/Sitka, single sides.
I have had good luck with maple inner/rosewood outer double sides but the customers wanted a traditional IRW OM sound so I went with single sides. Hope they like them.

IMG_8388 by Terence Kennedy, on Flickr

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Apparently I'm not getting around it- I reached out and was told I absolutely could not make these, in any way. I reckon I shouldn't be surprised, but I was- so much in the guitar community is treated as open source (to a degree), provided you are outspoken and transparent about the influence, which I would be. It was kind of shocking to hear that they would enforce the patent against someone as small time as me.

They did offer to make custom versions of their machines to meet the requirements I was after in making my own. We'll see how that goes.

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Burton
http://www.legeytinstruments.com
Brookline, MA.

Modulus Graphite once sent me a cease and desist letter back in the 80's because I happened to mention I wanted to make a couple carbon fiber necks. Since their parent company was Howard Hughes huge conglomerate, I had no way to combat their phalanx of lawyers, and dropped the idea toot suite.

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

New stuff in my shop: A refrigerated air dryer and point of use water/oil filter. After discussions with Brad Combs about the likelihood that a specific finish problem I have experienced is a contamination issue, I started looking for solutions in the form of a refrigerated air dryer, since I don't really have room for some of the other things one can do about this. I lucked into a steal of a deal on an open box, never used Saylor Beall model. I spent all last weekend incorporating the air dryer and filter into my air supply (I'm all out of love, I'm so lost without you--No, not that Air Supply) and building this rolling tower to house my compressor, the air dryer, and my shop vac (which lost its home to make room for the rest of this stuff):







Everything is working ship shape, and the rolling tower is very compact and convenient.

Dang. I never contacted him, but something had given me the sense he was that kind of person. Personally I would not give him any business... more tempting to take him to court over it just out of principle, since it is ridiculous to claim ownership of such an old mechanism. But like I say, strain wave is superior anyway, being one of the few inherently backlash-free mechanisms. And you're certainly welcome to join me in making them

Here are some exploded views of the current Blender model (I would include the .blend file too, but this forum only allows uploading image files. PM me if you want it). Hopefully this is enough to make the idea un-patentable for the future. The ring gear will either be press fit or glued into the housing, permanently closing it. Weight should be around 14 grams with a wood button, including the mounting screw and headstock bushing.

Dennis, I am interested in your design. I'll reach out and see if we can work on it together on it. I'm curious how thin it would have to be to deform consistently? Also curious how small those teeth really are

He mentioned that what was unique about their design was that clockwise rotation of the input shaft resulted in clockwise rotation of output- Apparently standard cycloidal drives reverse the rotation?

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Burton
http://www.legeytinstruments.com
Brookline, MA.

Direction just depends on which of the 3 components is input, output, and fixed. Page 32 in this document (a little over half way through, labeled page 10 in the engineering data section) shows all the combinations for strain wave, and cycloidal is more or less the same https://www.harmonicdrive.net/_hd/content/documents1/CSG-CSF_Component.pdf

The photo you posted looks like ring-out, so it would be same direction. Nothing novel about that. My design is reverse rotation, which I consider a worthy sacrifice for lighter weight. But you could design a strain wave where the flexspline is fixed and ring is the output, in which case it will rotate the same direction as the input.

And yes, the teeth are very small About 0.3mm tall, 0.9mm wide, and 2mm face width (limited by the length of the end mill). But since a lot of them are engaged at any given time, I think they will be strong enough. 120N string tension (about 27lbs) wrapped on a 3mm radius post gives 0.36Nm torque. The gear pitch radius is about 4.4mm, so that's 82N tangential force on the teeth. Assume contact angle is about 45 degrees, giving equal radial force, and it works out to 115N total force on the teeth. If 12 of the 30 teeth are engaged, that's right about 1kg/2.2lbs on each tooth.

But it would be no problem to rework it for a larger diameter gear if necessary. My design is ultra-compact, with the housing for the non-toothed portion of the flexspline sized to fit up inside a standard 10mm headstock hole. But even if you put the entire housing outside so it can use 1/4" headstock holes, it would still only be 9mm tall, and have no restriction on gearbox diameter. That would allow higher reduction ratios too, since you could fit more teeth of the same size. But personally I prefer lower ratios anyway, and I think high ratio will be even less necessary when you don't have to fiddle with backlash.

I don't know anything about the patent issues, but I know that I've worked with Bill Rickard on banjo matters over the years, and he's a first class guy. Might have some attorneys guiding him now, I don't know. But for anyone who doesn't know, Bill owns a CNC machine shop in Canada, and was a banjo player. He was also an avid motorcyclist, and had a terrible accident in Europe a number of years ago that cost him his left arm shoulder down and his entire left leg. dang near died. But as a major part of his rehabilitation after the wreck, he started working on ways that a one armed guy could still build and play banjos. He designed and built some really impressive machinery to be able to roll banjo rims one handed, etc. He built a pneumatic "left hand" that he could control with his remaining foot so that he could still play banjo. That didn't work out to his satisfaction, and he decided to focus on building rather than playing. At any rate, the focus helped him through some really bad times, and he's been continually improving and expanding his banjo parts line (in addition to his regular business). His banjo parts are absolutely top notch, and he's offering stuff to that community that had never before been available. His banjos are very nice as well.

But as I said, I don't know anything about the patent issues, But Bill Rickard is a real inspiration in successfully recovering from a tragic incident and letting that recovery lead him into a whole new thing. I only hope that, heaven forbid, if any of the rest of us ever find ourselves in such a situation, we can handle it like Bill has.

https://rickardbanjos.com/pages/bill-s-story

Dave

I'll add to what Dave said about Bill Rickard. He is an outstanding guy who's shared tons of info with fellow builders over the years. When I was building banjos he was pretty much the only source for many vintage style banjo parts and hardware. At the time, outfits like Gibson and Deering had access specialized hardware but those concerns wouldn't even sell parts to other builders. Bill filled in a lot of those voids and was a major asset to small shop builders and the community.

If memory serves me, when he started on the redesign of banjo tuners he ended up collaborating with Frank Ford (also a machinist) on design and mfg. Seems like they were working on the tuner project for a couple years, asking for input/ideas from builders and players. Then there was the testing and tweaking the design. Lots of work!

I think a project for a couple guys like that, to design, mfg and sell tuners made in North America is quite an accomplishment and they deserve every bit of patent protection available.

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Brian R, Wood Mechanic
N8ZED

I seem to remember meeting a Bill Rickard at Symposium in the late 80's. I think he was working for Ovation then? Or am I thinking of someone else?

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

Different Rickard I think Chris. I think Bill had a big manufacturing biz (factory) in Ontario where he made things for the trucking industry. Seems like I remember conveyors and stuff. Not sure he is still involved there.

I think he got into banjos post the accident around 2005 or so. I could be wrong, just from memory talking to him on the phone and the Banjo Hangout.

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Brian R, Wood Mechanic
N8ZED

Yes, different Rickard at Ovation--I think he was James. Did most of the R&D for them. I think I met him at Symposium too.

Dave

JAMES. That's it, guys. Thanks for shifting my brain.

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

The pictures of these two different Rickards in my mind are James sitting in front of an oscilloscope and Bill sitting in front of some big bizarre one-handed banjo making machine!

There was yet another Rickard in the banjo world (don't know if he's still out there or not), Gil Rickard from Connecticut or somewhere up that direction that made really nice vintage banjo hardware before Bill Rickard was making his. I've gotten a lot of banjo parts from him and from Bill.

There's a guy in North Carolina, not too far from me, who bought out Stew Mac's old Waverly machinery that they had bought from Waverly, who is making great vintage banjo parts. Some of this equipment goes back to the thirties or maybe even earlier. He owns Pisgah Banjos and Balsam Banjo Works. Glad there was someone interested in getting it--otherwise it would have probably ended up in a scrap metal heap. It's a shame that all of this happened at the time when I pretty much shut down banjo building operations!

Dave

Dedicated thread for strain wave tuner discussion: http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=55598