On Tuesday 16 August 2016 22:37:48 Martin Dobbins wrote: > Sherline lathe motors are not known for torque at very low speeds, > which is probably why Sherline sells this piece of kit for cnc > threading: > > http://sherline.com/product/6500-stepper-motor-mounting-kit/ > > This will work (very slowly!) for cnc threading if a modest size Nema > 23 stepper motor is used. Some folks get a little tired of waiting > and swapping back and forth between stepper and regular motor for > turning and threading. > > A couple of people came up with this setup: > > Stepper KL34H2160-62-8A; 1810 oz-in NEMA 34 > Stepper driver - MA860H > Power supply - 500W Rockstone step up/step down transformer. > Spindle is geared 1:1 with stepper > > The stepper driver can accept a maximum of 80V AC or 110V DC. The > power supply (Amazon sells it) can accept several voltage inputs > stepping down to 110V AC, one of which is 200V. 200V:110V is .55% > reduction, so input 110V into the 200V and out comes ~60.5V which is > fed to the stepper driver. > > Apparently this cost effective solution results in the ability to turn > and thread with only a tool change in between and reasonable DOC on > the threading so that it doesn't take forever. > > The whole shebang is controlled by a PIC microchip, which also > measures the output of a spindle encoder on the lathe (10 pulses per > revolution IIRC) and then "sends" one ppr to Mach 3 to coordinate the > the Z axis. > > This looks a promising solution, and I think with Linuxcnc, the > microchip could come out of the equation. > > I came across Clearpath servos and wondered if this might be a more > elegant system? > > https://www.teknic.com/products/clearpath-brushless-dc-servo-motors/ > > The trouble is I know nothing about servo driven spindles, would they > have the same problem with poor torque at low revs that the Sherline > DC motor does? Since the integrated drive and controller must be > measuring servo spindle speed/direction, couldn't I use that (if I can > actually access it!) for lathe spindle speed?
Looking at the torque curves of the SDSK series, and the steady state available powers, for a spindle drive the steady state limit is the important one, and its much lower than its peak torque while moving to a fixed position. You have to get large and ex$pen$ive to get steady state above 250 oz/in at a usable rpm. You may want to check out the MC series which are brushless servos internally. I'd have to assume they also would overheat in a steady state run at a given load. You can only pack so much horsepower in that volume before something gets too hot. 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> ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
