Centroid Acorn Plasma Users Manual Beta CNC12 v4.65 rev6
2.) Once the bench tests has been performed its time to install, setup and configure the XYZ axes to get basic CNC
motion.
See Acorn Installation manual for non plasma related wiring and configuration such as axis motor drive wiring and
setup, overall turns ratio, homing options etc.
https://www.centroidcnc.com/centroid_diy/downloads/acorn_documentation/centroid_acorn_install_manual.pdf
Important details for good Plasma machine performance not to be overlooked.
- When using open loop stepper motors it is imperative that the motor, drive and power supply be matched/balanced
and configured properly. Just because it runs doesn’t mean it is configured properly for best performance. Be sure
to follow the guidance found here from GeckoDrive. https://www.geckodrive.com/support/step-motor-basics.html
Better yet, use any of the affordable Closed Loop Stepper or AC motor/drive packages now available. There is
really no real cost savings in using open loop steppers any more and the performance advantages of closed loop is
tremendous in operational time savings and machine performance. (better smoother cuts with less waste/mistakes).
- The ‘sweet spot’ for Plasma Table mechanical design is so that the machine operates anywhere in the range of 1 to
2 turns of the axis motor yields 1” of travel for the X and Y axes. Direct Axis motor to Rack Pinion driven machines
do not provide the best cutting results. A gear box or belt reduction is highly recommended on rack driven machines
so one rotation of the axis motor will result in a least 1” of axis travel, more is better. Arrange the mechanicals to be
in the 1 to 2 inch of travel per one revolution of the Axis Motor. Typical gear box/belt reduction ratios used on rack
drive Plasma machines are 5:1 and 3:1 which one you use depends on the pinion diameter being used.
- If you are coming from Mach, LinuxCNC or other DIY cnc controllers be sure to set Acorn ‘steps per rev’ and the
‘overall turns ratio’ properly..see this post
- Plasma Table Z axis Overall turns ratio is ideal at 2.5 turns per inch. Range for good performance 2.5 to 5 turns
per inch. Note: More reduction results in slower Z axis max rate. 5 turns per inch (a common ballscrew pitch is
5mm which = 5.08 turns per inch) can be used just be sure to have a Z axis motor that has the RPM and power
rating to operate the Z axis at least 500 ipm reliably. Highly recommend a Closed Loop motor/drive on the Z axis of
a Plasma machine.
- AC servos on all axis are the best solution. If budget is a consideration use Closed Loop Stepper motors. At this
day and age it is really not cost effective to use open loop stepper motors any more, but if you insist at least install a
Closed Loop Stepper on the Z axis. Like this. https://www.automationtechnologiesinc.com/products-page/nema34-
closed-loop-stepper-motor-system-hybrid-servo-kit/nema-34-hybrid-servo-motor-kl34-8n-1000-rated-torque-1128-oz-
in
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