On Friday 15 December 2017 11:11:32 John Kasunich wrote: > On Fri, Dec 15, 2017, at 06:16 AM, andy pugh wrote: > > If you look at stock internal gears: > > http://www.hpcgears.com/pdf_c33/17.7.pdf > > You will find that getting a pair that differ by only one tooth > > isn't that easy. And they will differ in PCD. The PCD difference > > isn't to hard too deal with in external gears if you can make them > > big enough for the corrections not to distort the teeth too much, > > but it would be much easier to not have two PCDs on the planets. > > So, you would ideally be making your own internal gears. > > I believe it would be possible to design a similar drive using the > same internal gear for both the grounded ring and the output ring. > All the gears would have standard tooth forms, and could be > off-the-shelf. > > The trick is that the planet gears centers would have to be at > different radii. So instead of the two sets of planet gears running > on the same planet carrier pins and being fastened to each other, you > would have two sets of planet carrier pins (probably on opposite > sides of a planet carrier plate). The planets would all be > independent. One set would have N teeth, the other set would have N+1 > teeth. The sun gear would be two stacked and coupled gears, one with > M teeth (meshing with the N tooth planets) and one with M-2 teeth > (meshing with the N+1 planets). > > Not sure if what I'm describing is still a wolfrom drive, but it would > have the same result - a very high reduction from planet to output > ring.
That sounds like a quite practical thing once the math has been worked out. And it also sounds like it would be a heck of a lot more efficient assuming the planets were running on caged needle bearings. Ratios high enough they could be a rotary table drive, and most certainly less backlash than my current 4 incher has which is tight at some positions, and a good degree at others. I just yesterday watched a guy build a std planetary set using blender, which in turn allowed the wireframe to be animated for proof of concept. I had no idea blender had all those capabilities. I believe it can actually export g-code too. But something along these lines, using gears maybe 1/4" long, sounds like it could be stacked in a rotary table casting, one that could be moved by a nema23 motor while resisting cutting forces. Mine can't even do that when stationary due to the backlash. Piece of junk from India for a smidgeon over a $100 bill today, I doubt its accurate enough to do a usable gear. Those 1/8" thick, #25 chain sprockets I made that one of you kind folks wrote the gcode for me several yeas ago, I cut with a new 1/8" 4 flute carbide tool, and due to it moving to the other side of the backlash on opposite faces of the tooth, cut the teeth wide enough that I had to file the wider part of the tooth about 4 strokes of a fresh mill bastard on each side of the tooth before the tooth would properly enter the inter-roller spacing of the chain. And while it still runs "lumpy" it does get the job done, which was driving a taller fence with a couple pieces of 1/4" redi-thread on my bandsaw so I could move the fence while maintaining the drift angle well enough to cut about 3/16" slabs of butternut out to make panel inserts for all our kitchen cabinets. Butternut I got from Ray Henry on one of my trips to the UP. I am "intrigued" if you've time to hack up some drawings. I have 1/2" thick micarta which could be used for a proof of concept. Highland Hardware in Hotlanta has more of it. And I have about 8" or so of 1" Acetal rod for the planetaries. I bought it to hot mold zero backlash nuts from, then bought some teeny ball screws instead from Stuart S. Heck of an idea John. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
