View Full Version : Mechanical Questions From a Newbie CNC Plasma Table Builder

01-11-2011, 10:46 AM
Hi group,

At this moment I am pretty well versed in the CNC lingo and heuristics. I was able to build an operate a CNC router, although I have not built anything with it. The reason? There is nothing I want to do with wood, actually. I prefer metal. Hence, I will change my table to a plasma cutter. This in turn results in a gazillion questions maybe somebody in here can help me with:

1. It seems plasma cutter tables utilize the rack-pinion system instead of the lead screw venue. That makes sense as the long X Axis lead screw would get obliterated from all the molten metal debrie falling on top of it. I found some nice Rack Pinions Gears at MacMaster but I can not find information anywhere on what pitch/angle to use. Should I go with a smaller pitch and pay a little bit extra or does it not matter for this kind of application? How about angle? What does 20 versus 14 degrees give me?

2. Assuming I will do the rack and pinion deal, with the stepper running on top of the rack gear, do I need two of these drives for the X Axis? I think I have seen tables with a single motor for the X Axis, but then it is my impression that the motor side will move and the other side will attempt to follow, with some possible warpage on the Y Axis. Is this real, or does a single motor does the trick with no penalties on precision across the X Axis? I have seen machines with the dual motors and dual rack and pinion but not only this makes the X Axis twice as expensive, I would need to match both threds as much as possible in order to minimize deflection.

Thanks for any info you can offer on these questions!

Best regards,


01-14-2011, 11:25 PM
To answer question number 2. You need to have dual side drive to prevent racking.

Now, this does not necessarily mean 2 motors, you could use a driveshaft to connect both sides. You should also look into timing belt drive, its cheaper than R&P, works good and may be easier for you to implement on your machine versus R&P.