On 6 March 2010 07:58, Erik Christiansen <dva...@internode.on.net> wrote:
> In MEW 75, another author used a couple of CMOS chips for the > programmable divider between the spindle encoder and stepper driver, to > select the number of teeth. This is very easy to set up in HAL (and quite amusing too, watching the rotary axis turn as you turn the chuck to tighten it, for example) > That setup has the hob running on a mandrel between lathe headstock and > tailstock. The stepper-driven spindle holding the gear blank is mounted > on a vertical slide on the cross-slide. That is probably the setup I will try first, mainly as it needs the least extra hardware. > From the photographs, that makes > the feed perpendicular to the hob axis, which seems to me to ignore the > helix angle. How that creates a spur gear with proper gaps, is not clear > to me. I don't think it does. I was intending to set the vertical slide at an angle and use coordinated motion in X and Z so that the blank moves along it's true axis. > On the other hand, preferring the quiet running of helical gears to the > whine of spur gears, I have run the above setup in my mind, with (a > virtual) EMC advancing the phase of the gear blank as it is fed across > the rotating hob. If the rate of phase advance matches the helix angle, > then the blank should come out the other side as a helical gear, I > believe. (And both blank and feed are perpendicular to the hob axis. > What could be simpler?) I am not sure. It depends in if a helical gear is conceptually a gear with the teeth rotated on the surface, or a stack of infinitely thin gears with a pitch difference between each. In this picture: http://school.mech.uwa.edu.au/~dwright/DANotes/gears/photos/BrownHobbing.jpeg The hob axis seems to be tilted to match the gear helix angle, rather than the hob helix angle. I think that in either case you ideally want to match the hob helix angle to cut a true gear form. I did discuss this with my dad (50 years a gearbox machinist then designer then service manager) but he seemed unable to grasp that the feeds and drives are trivial with CNC, but the axis geometry is less so) -- atp ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
