RE: [CAD_CAM_EDM_DRO] Z Axis motor speed

On the router / mill table I am building I have chosen a 24 Volt DC motor to
drive the Z axis ball screw. The motor is rated at 15 Amps with a speed
rating of 500 RPM.

The motor is directly coupled to the ball screw and a 2000 line per rev
shaft encoder which when calculated gives me 200 steps per MM of travel on
the axis.

The Z axis is able to travel 160 mm and the accuracy and torque I am getting
are better than expectations.

My problem though, is that the positioning speed (especially on tool
retraction) is very slow, and when drilling 1200 holes in an ali plate the
other day for a vacuum table - it took forever !! From this experience I can
see that the slowness of the Z drive will be a major delay in the 'job
cycle' for any serious future projects like 3D milling.

The Z axis is loaded with quite a bit of steel and an 1800 Watt router, the
current peaks to about 5 Amps when the axis moves up and the DC supply drops
from 25 volts to about 22 volts - I don't think from these results that any
of the mechanics or power supply are in any way overloaded - just that the
motor (as designed) cant run fast enough.....

I have another DC motor rated at 80 Volts, 45 Amps with a quoted RPM of
4,500. I would think that the developed torque will be adequate, but don't'
want to do a load of metal work and machining new couplers etc to find out
that the new unit is too damn fast and may compromise the accuracy I am
happily achieving !

Machine line up -
RUTEX servo amps x 3
DeskCNC sofware and driver board

Any comments or suggsetions would be most appreciated.

Rgds

Dave Fisher UK