If you want to machine, not print the gears then I'd think then if you have 4 axis CNC you could just route the internal teeth with a straight end mill. The trouble is the minimum radius is the size of the end mill and you need a really tiny end mill to make the last finish pass. But if you cut the internal teeth a little bit deep a to large radius would not matter. You could also do the final pass with a broach
Google for pyGear. Looks to be a very good and free gear design software, Open Source. https://sourceforge.net/projects/pygear/ also a simple browser based gear designer that can export DFX http://hessmer.org/gears/InvoluteSpurGearBuilder.html On Fri, Dec 15, 2017 at 3:16 AM, andy pugh <[email protected]> wrote: > On 15 December 2017 at 01:28, <[email protected]> wrote: > > I make plastic gears on a table top cnc mill > > Just things for toys and do-dads > > The reason I asked is that external gears are easy to make, but > internal ones are not. > I make gears for fun, here is a triple coaxial differential gear: > https://photos.app.goo.gl/XaCm1X9HFRKH8fgt1 > > But I use the hobbing method of gear making, and that can't be used > for internal gears. > > To make internal gears you need a Fellows-style gear shaper > https://www.youtube.com/watch?v=UNenwSSZfYU > > (Which would be a fun modification to a slotting head on a milling machine) > > 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 guess it would be possible to single-tooth shape the internal gears: > https://www.youtube.com/watch?v=W69m2cDaqvY > (Or maybe not, my visualisation skills are letting me down there) > > -- > atp > "A motorcycle is a bicycle with a pandemonium attachment and is > designed for the especial use of mechanical geniuses, daredevils and > lunatics." > — George Fitch, Atlanta Constitution Newspaper, 1916 > > ------------------------------------------------------------ > ------------------ > 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 > -- Chris Albertson Redondo Beach, California ------------------------------------------------------------------------------ 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
