Hi, I'm new to CNC Plasma cutting and need some help.:confused:

I've build a 3-axis CNC machine to run a router on it and it worked very well.
A while ago I decided to put a plasma cutter on it. I'm using a Thermadyne Inverter type with high-frequency arc start.

The problem is, as soon as I "trigger" the plasma arc my computer pickup interference and either hangup or start with alarm beep and lose control of most functions.

I've tried to isolate the cutting table from the gantry but it doesn't help. Even with the plasma cutter removed from the cnc machine and positioned 10' from the computer the problem remain the same.

I assume the problem is the high-frequency arc, if so, how can I get arround this problem?

I've had a little experience with a plasma causing one of my PC's to reboot. I'd say that the motherboard had a design weakness that made it susceptible to the RF noise.

Best to try a different PC. Before you actually go to all the work of changing over the PC in your control, you can just set up the prospective PC near the same location, and fire up the plasma and see how the PC reacts.

Run the PC through a battery backup type UPS (surge protector). You should already be doing this.

Grounding for noise and grounding for AC safety are two different topics. The HF noise from older plasma cutters is a real problem. If it reboots you computer it most likely will cause problems in the motion control electronics.

Make sure your computer is not grounded locally to the table or the plasma side.

It's ground needs to be from another source. Depending on the motor drives, power supply and control electronics you may not have the option to run a two ground system in which case you may have to put your PC inside a metal enclosure not connected to the table. We have several customers running MACH on a PC with our Digital THC with old HF start plasmas but they had to go to extreme grounding techniques to make it work.

TOm Caudle
www.CandCNC.com

After some testing, it seems that "extreme grounding" should solve my problems.

Thanks for advice and info.

After some testing, it seems that "extreme grounding" should solve my problems.

Thanks for advice and info.


In the wonderful world of plasma, there is no such thing as "extreme grounding"

Very common problem with HF plasma systems. The first thing you should do is go to a plasma manufacturers web site, such as Hypertherm or Thermadyne and research the proper grounding techniques for providing a proper ground for plasma. One thing to remember is that just because a ground rod is driven into the ground, does not mean that it is 'connected' to earth ground. This is usualy the most common fault of plasma interfernce. People think that their ground rod is making earth ground just because it is in the ground.
Once a good earth ground is established, follow the plasma manufacturers recommebdation for grounding the plasma and the table.