[mcArch]

Thanks nicjac, I cannot isolate the cutting bed on my machine because it's all an integral table, but I'm working on it today.

Jim, What about the plasma chassis ground that connects to bldg. ground? The ESAB unit has the power cord ground attached to the unit chassis inside, so if I run another ground to the star point on the table, (or directly to the 8' rod then it will be grounded both through bldg ground and my plasma table earth ground?

Thanks for the input guys!

[jimcolt]

The chassis ground that goes to electrical ground can create a "ground loop"....which can be problematic for noise......but safety concerns must overide that. I would suggest leaving the electrical ground as it is....but still ground the chassis to the ground rod. Ideally the plasma power supply should be very close to the ground rod.

The goal is to get stray RF to follow a path of least resistance (large surface area conductors) directly to the ground rod. If there is any daisy chaining....it won't be direct!

I have seen many sites over the years with noise issues (on big industrial machines) that had an overly complicated grounding system.....by simplifying it we were often able to eliminate the problem. Isolating the torch leads is the #1 best cure!

We run high frequency plasma cnc machines at every trade show....with absolutely nothing but the electrical ground....with no problems whatsoever. We do pay special attention to routing of all leads and cables on these machines. Motor and encoder cables are low voltage, and the RF from the high frequency loves to inductively couple to these cable....wreaking havoc with the computer.

Many of the newest industrial machines today use sercos drives all linked with fiber optics. noise problems eliminated!

Jim Colt

[jimcolt]

One other comment.....I would not attempt to isolate the table from the rest of the machine.....could be dangerous. All metal surfaces need to be at the same potential as the ground rod. Plasma systems can have open circuit voltages of 400 vdc.....if the table was isolated...and some sort of electrical failure ocurred within the plasma system...you could have some lethal voltages present.

jim colt

[mcArch]

I have a 6awg stranded ground that runs from the Z carriage to the gantry, then one from the gantry to the table . . . maybe that daisy chaining is part of the issue. I'll get those running right down to the 2/0 ground cable connection point on the table. That 2/0 cable is 5' long going directly from the table leg to the 8' ground rod.

Thanks Jim for the info. I'm still working on it.

[jimcolt]

I would run the each directly to the ground rod. If you are picking up noise on the carriage...a very likely place because the torch is mounted there...then you are now carrying this RF to the gantry by daisy chaining these connections.

I would clean up the grounding a bit...then isolate the torch leads by pulling them completely off the machine....you could even have someone hold them up away from everything (I always bring a helper!) while you fire the system.

Another fix that occasionally works.....find the spark gap assembly in the high frequency circuit of your plasma system. The gaps are probably set at .015" to .020" ....remove the tungsten rods, clean them up and file the ends (only with a diamond file....a steel fill will contaminate the tungsten) perfectly square and sharp. Re-install the tungsten rods and try closing the gap up to less than the manuafcturers specs....this will diminish tha starting voltage. If you close the gap too much the torch will misfire...so you want to balance this carefully. If the tungsten gaps are worn and rounded....your starting voltage will be very high (because RF travels on the outside of conductors)...and may be causing your problems.

Good luck, Jim

[andyleahy]

Hello,

We have recently retrofitted a 6m by 3m S.A.F. Plasma cutting table.
The machine works great however, the arc transfer creates noise which is interfering with our control and P.C.

I will list components used and current grounding techniques below;

Plasma Source : MaxPro 200
Control : Usb Version of Flashcut CNC Controller
Motors/ Drives: Clearpath Stepper Servos (SDSK) type.
Pc: Standard consumer grade Lenovo.

The cnc controller and PC is located in the control cabinet which is located on the gantry.
The Plasma unit is located beside the table aproxomatily 1m.
The plasma hose runs in a cable chain distance of 150mm from other signaling cables.
In this cable chain a usb and hdmi cable are also run to a standalone control console.
At the end of this cable chain (gantry side), the plasma hose is physically 800mm from all other cables on it's route to the torch holder.
I currently have the plasma hose shield grounded on both the Z axis frame and on the plasma unit side to copper grounding rods. The machine is grounded to hypertherms reccomendations. I had this grounding checked be by a third-party company locally. Incase I was missing some (simple) grounding.

Currently the Flashcut Control is losing it's USB connection to the PC as soon as the torch fires.

Any help would be greatly appreciated.

My next steps are
To physically distance the plasma hose completely by hanging it down from above.
but beyond this Im not sure what else I can do.

Is Flashcut the issue as its USB connection?
Would an ethernet controller be a better solution?

Thanks

Andy leahy - Ireland.

[datac]

Is Flashcut the issue as its USB connection?
Would an ethernet controller be a better solution?

Flashcut shouldn't be your problem.... I have used Flashcuts USB version on more than one Plasma Table without issue, and always with Hypertherm units. My current machine has the PC outside of the Cabinet with power supply and drivers, fed with a 10-15 foot quality USB cable. I'd expect problems with that length, but I have none currently. I always ground the plasma cutter right to the plate I'm cutting, and the drives, limits and motor wiring all use common star grounding, with all cable work ONLY grounded in/on the cabinet. Cabinet is bolted right to the machine frame.

First, I'd try a quality USB cable. If that does not help, Flashcut is easy enough to install on another PC or laptop. Install it, copy the Setup file to the Laptop, open Flashcut and load the setup file.

Try running the machine on a longer cable away from the machine. Certainly worth a try as Flashcut is not an invasive program and any laptop will do for a test. If you get better results, You could first swap in a newer or better PC power supply in that Lenovo, reseat all the PC's boards and memory cards, and even use a DIFFERENT 110v power source for it.

One more thing... make sure you have a really good 9v supply for the SIgnal Generator. I've found that it needs a good solid 1 amp or higher wallwart. I've had isues when the PS was not up to snuff.

Lastly, you could give Flashcut a call.... they have put pretty much all their energy in the last few years directly towards Plasma cutting specifically and there is no way they would be successful if it did not work.

Good Luck !