On 10 October 2016 at 04:04, <richsh...@comcast.net> wrote: > OK guys, I constructed a basic set of specifications for my gear hobber and > would like all the directed wisdom be used.
(A lot of people might not have spotted the PDF tagged on to the bottom of a digest) I am not sure that you need an encoder on the spindle drive motor, but you do need an encoder on the spindle. It my be that it is simply easier and cheaper to have the encoder on the motor and correct the ratio, but you will need backlash-free drives. The same is true of the work axis. The work axis will need to rotate at 1/8 to 1/100 (or so) of the spindle axis, so having the same gear ratios seems somehow wrong. I have hobbed quite large gears with a 2hp milling spindle for the cutter and a 100W servo (geared 90:1) driving the blank. I suspect that was more power than the cutter needed, and was marginal on blank rotation torque. I think that my starting point would be the recommended cutting speeds for gear hobs in conjunction with the hob size range supported to choose cutting spindle speed range (and your 3:1 ratio might well be correct there) and from there work back to the speed range needed for the workpiece. If you then consider the cutting torques on the two spindles you should be able to decide what is needed for the work spindle. Free-wheel hobbing can work quite well, so it may be that the workpiece torque can be lower, but I can imagine that helicals. for example, might need to be held quite rigidly as the cut is less symmetrical. Ideally you would have a super high resolution encoder directly coupled to the work spindle. I doubt that can be done cost-effectively though, so having the encoder on the motor geared 50:1 or so might be the best arrangement. -- 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
