CAD CAM EDM DRO - Yahoo Group Archive

cnc spindle speed for small 1HP-2HP lathes

Posted by Doug Fortune
on 2001-10-14 12:58:09 UTC
I've been speaking with DaveK (TurboCNC) regarding controlling
the spindle speed. I suggested using a low-medium resolution
encoder on the spindle, and using a 1HP DC motor to run the
spindle (through the existing belt or gear drives) - if the
encoder is attached to the spindle, the spindle speed is what
is governed, even though the motor may actually be at a different
gear ratio.

For example, using the Leeson DC (SCR/PWM qualified) 1 HP motor
(90Volts @ 10Amps @ 2500 rpm $490 list) model#108020 and a
Gecko 340 (77 Volts @ 10 Amps with my Powersupply), then the step
rates are as follows for different encoder resolutions and Gecko
step multiplier settings (at a top speed of 2500 rpm = 41.6 rps):

50 line = 200 counts/rev
Gecko *1 mode 8333 pulse/sec (ie 41.666 * 200 count)
*2 mode 4166
*5 mode 1666
*10 mode 833

100 line = 400 counts/rev
Gecko *1 mode 16,666 pulse/sec (ie 41.666 * 400 count)
*2 mode 8,333
*5 mode 3,333
*10 mode 1,666

200 line = 800 counts/rev
Gecko *1 mode 33,333 pulse/sec (ie 41.666 * 800 count)
*2 mode 16,666
*5 mode 6,666
*10 mode 3,333

500 line = 2000 counts/rev
Gecko *1 mode 83,200 pulse/sec (ie 41.666 * 2000 count)
*2 mode 41,666
*5 mode 16,666
*10 mode 8,340

1000 line = 4000 counts/rev
Gecko *1 mode 166,666 pulse/sec (ie 41.666 * 4000 count)
*2 mode 83,333
*5 mode 33,333
*10 mode 16,666

Obviously the 100 & 200 line encoders would be good for the
8K step/sec type interpreters (ie Master5), while EMC, TurboCNC
and cncPro might be able to use the 500 line encoder to give
a somewhat greater resolution.

The advantage is that the gcode interpreter program just has
to send out the steps at the correct time, it doesn't have to
worry about the servo-feedback loop (the G340 does that).
The index channel can be used for a reference for thread
starts.

Also note that 1HP is the reasonable limit for this strategy
(because I haven't found any 90V DC motors that have current
capability past 10 amps - whereas the Gecko has a 20 amp capacity
so theoretically the limit is 20*90 = 1800Watts or about 2.5 HP).

Doug Fortune
http://www.cncKITS.com

Discussion Thread

Doug Fortune 2001-10-14 12:58:09 UTC cnc spindle speed for small 1HP-2HP lathes