It is currently Tue Oct 16, 2018 10:37 am

 

Grounding the CNC table?

CNC Plasma Cutters are amazing and there is always plenty of knowledge to share and discuss. Use the CNC plasma cutters general forum for this purpose.
anarc
Posts: 7
Joined: Fri Apr 20, 2018 5:20 am

Grounding the CNC table?

Postby anarc » Fri Apr 20, 2018 5:45 am

Hello plasmaniacs,

I am a bit confused about grounding the CNC table.
All those things I read just confuse me more :-(

Most threads talk about putting the ground clamp to the material.
But in fact the clamp to the material is (+) , not ground.
So why is everybody speaking about ground?

If I use the plasma torch manually there is just the + clamp and the - torch and the grounding of the inverter of course which is grounded through the power grid.

So I assume the grounding is just to protect the CNC electronic from potential peaks? Not for my personal safety?

Currently my water tub is not connected to the table, nor is the torch as it got a plastic handle. The rest of the table including the motors housing are connected.

I read it is useful to ground the portal and the z-axis but for what scenario?

thanks

anarc

User avatar
WyoGreen
Elite Contributing Member
Elite Contributing Member
Posts: 674
Joined: Tue Mar 04, 2014 8:36 pm
Location: Cheyenne, Wyoming

Re: Grounding the CNC table?

Postby WyoGreen » Fri Apr 20, 2018 11:38 am

Good grounding practice is to connect the frame of the table to a separate ground rod located close to the table. The reason for this is cut down on noise generated by the plasma arc from affecting the motor and data cables on the table.

You are correct that the plasma machine clamp is not ground. It is the return path for the current from the plasma torch. Best practice on that is to connect it to the material being cut to ensure a good return path to the plasma cutter.

Steve
Precision Plasma gantry
CommandCNC Linux controller w/Feather Touch & PN200 hand controller
HT-45 plasma cutter
Plate Marker
CNC Router table

User avatar
tnbndr
Elite Contributing Member
Elite Contributing Member
Posts: 1411
Joined: Mon Jan 09, 2012 4:30 pm
Location: New Berlin, WI
Contact:

Re: Grounding the CNC table?

Postby tnbndr » Fri Apr 20, 2018 11:47 am

You are correct the plasma clamp is not a ground but the +. People think of it like a welder so call it ground or negative. Most of us understand so don't correct. But that + clamp should be directly to the material you are cutting, not just the table or slats.
Dennis
LDR 4x8, Scribe, DTHCIV
PM45
DeVilbiss Air America 6.5HP, 80Gal., 175psi, Two Stage
[email protected], [email protected]
Miller 211
RW 390E Slip Roll
AutoCAD, SheetCAM, Mach 3
https://www.facebook.com/ikescreations?ref=hl
http://ikescreations.com

User avatar
acourtjester
Elite Contributing Member
Elite Contributing Member
Posts: 3144
Joined: Sat Jun 02, 2012 6:04 pm
Location: Pensacola, Fla

Re: Grounding the CNC table?

Postby acourtjester » Fri Apr 20, 2018 1:05 pm

On the plasma unit it is call a work lead, This helps to keep the polarity clear.
As with many electrical things you have a circuit and the more connections in a circuit the more problems.
Attaching the work lead to the metal being cut gives you the best path for the plasma circuit, going through slats and table frame just adds to the number of connection. The arc OK is a check of the current path for the Plasma circuit, no path no cut.
DIY 4X4 Plasma/Router Table
CandCNC DTHC-IV & Feather Touch
Hypertherm PM65 Machine Torch
Drag Knife and Scribe
Miller Mig welder
13" metal lathe
Small Mill
Everlast PM 256 tig

anarc
Posts: 7
Joined: Fri Apr 20, 2018 5:20 am

Re: Grounding the CNC table?

Postby anarc » Fri Apr 20, 2018 1:29 pm

Thanks for the replies. Yes, I read about the rod in the ground but I have no idea how I´d get a 8' rod of copper into the ground. I could split computer and plasma using different phases but the ground would still be the same so that is probably not a good idea either. Any good guess to get around the grounding using the rod?

djreiswig
Elite Contributing Member
Elite Contributing Member
Posts: 339
Joined: Thu Nov 19, 2015 10:02 pm

Re: Grounding the CNC table?

Postby djreiswig » Fri Apr 20, 2018 1:33 pm

I don't have anything grounded on my table other than the power connections and I have had no issues with noise, so I'm not convinced it's all that necessary. JMO.
2014 Bulltear (StarLab) 4x8
C&CNC EtherCut
Mach3, SheetCam, Draftsight
Hypertherm PM65
Oxy/Acetylene Flame Torch
Pneumatic Plate Marker, Ohmic, 10 inch Rotary Chuck (in progress)

anarc
Posts: 7
Joined: Fri Apr 20, 2018 5:20 am

Re: Grounding the CNC table?

Postby anarc » Fri Apr 20, 2018 1:35 pm

So you grounded the table on the power grid ground or not even that ?

djreiswig
Elite Contributing Member
Elite Contributing Member
Posts: 339
Joined: Thu Nov 19, 2015 10:02 pm

Re: Grounding the CNC table?

Postby djreiswig » Fri Apr 20, 2018 1:39 pm

Plug the plasma in to a 220 cord with a ground wire, and the controller into a 110 cord with a ground wire. That's it.
2014 Bulltear (StarLab) 4x8
C&CNC EtherCut
Mach3, SheetCam, Draftsight
Hypertherm PM65
Oxy/Acetylene Flame Torch
Pneumatic Plate Marker, Ohmic, 10 inch Rotary Chuck (in progress)

jimcolt
Elite Contributing Member
Elite Contributing Member
Posts: 2939
Joined: Mon Jul 20, 2009 11:18 pm
Location: New Hampshire

Re: Grounding the CNC table?

Postby jimcolt » Fri Apr 20, 2018 2:10 pm

The cable that goes from the plasma cutter to the cutting slat bed is called the "work cable" by Hypertherm and other plasma cutter manufacturers, has never been called a ground cable. If you are not having any electrical noise related issues and are using an air plasma cutter with blowback start technology (all Hypertherm Powermax systems), then there generally is no need for an earth grounding rod. If you determine you need an earth ground rod it should be installed as follows: 1. Driven about 8' into the ground right next to the cnc table for best effectiveness. 2.Run the work cable from the plasma cutter directly to the ground rod, do not use the clamp, rather the cable should be bolted to the rod. The cable also must be cut to the exact length it takes to get to the rod, so shorten it and do not coil. 3. A short length of the same type and size of multi stranded (do not use less strands or single strand....as RF electrical noise travels on the outside of conductors and most efficiently gets to earth on multistrand cables) should be connected from the ground rod to the slat bed frame (bolted to clean, unpainted metal). If you desire a cable with a clamp as well, connect it (bolted) with the other cables from the ground rod....and leave just enough length with a clamp on the end to clamp to your plate. (note, I have been plasma cutting in my home shop for over 20 years....never once had an issue that required I clamp the work cable to the material) While on the subject...another help for electrical noise related issues on a shop cnc machines is to get a good quality UPS (uninterruptible power supply) as used for office equipment. Plug the 120 volt for your computer and the 120 volt for your drive electronics into the filtered, protected outlets on the UPS. Make sure the UPS is sized for the combined Wattage for the electronics and computer x 1.5. Jim Colt Hypertherm

anarc
Posts: 7
Joined: Fri Apr 20, 2018 5:20 am

Re: Grounding the CNC table?

Postby anarc » Fri Apr 20, 2018 3:28 pm

Thanks for the detailed answers! Very helpful.

lcrepairs
Posts: 1
Joined: Sun Jun 10, 2018 4:23 pm

Re: Grounding the CNC table?

Postby lcrepairs » Sun Aug 05, 2018 1:23 pm

Thanks guys for discussing this, I'm expecting a new TruCut XT table in a few weeks and I've been thinking how I could possibly drive a dedicated grounding rod in the ground since everywhere on my place has rock around 24" deep. I have my shop grounded to a shallow ground rod and everything is also connected to my house ground rod (So double covered) My metal building is also connected to all that, so why in the heck (in my mind) would I need yet another ground rod just for this table? I'm listening but so far can't understand that. I was told yesterday by a shop owner that he had trouble with his table until he put a 12' ground rod in, there has to be more to it than that. I'm not completely dumb to electrical and electronics, been fully certified in the automotive business for many years. Thanks for the above info and anymore that someone could add to my specific situation. Larry R.

tcaudle
Posts: 1034
Joined: Tue Feb 28, 2012 6:47 pm

Re: Grounding the CNC table?

Postby tcaudle » Sun Aug 05, 2018 2:57 pm

"Ground" is a misused term. The "ground" on your car is not the same as an Earth ground because you are riding on rubber tires. it's more appropriate to call the negative 12V as "Common" or "return". A plasma Work Clamp is just one side of a power source. It's important to understand there is no perfect ground and when you connect two system to each other any noise or difference in potential on one will transfer to the other even across a ground. So the plasma which is lots of current and lots of voltage puts its noise onto any thing its connected to . There is a distinct difference in a Safety ground (to connect equipment and AC common to a ground) and a noise ground that is designed to shunt HF noise to a low impedance. The table does not need a safety ground since it is difficult to get shocked when there is no return path to common for the plasma volts. When we call for a ground rod at the table it's less for any safety than to try and keep the table structure from becoming an antenna and transmitter.

It will actually work against you if you tie the table structure to the AC safety or Neutral side. Any noise on the table then hops up on the ground over to the controller. The closer its ground is to the noise source the worse it is. Its better to have no ground on the table than to tie it into the building AC ground . Lots of tables work fine without a local ground rod. No two grounds more than 10 ft apart are at the same potential . While a few volts of difference between grounds for safety is fine, a few volts of noise on a computer or logic level electronics can be a problem.

Noise and EMI /RFI travel differently than DC or low freq (60 hz) waves . So noise and safety have different considerations. Plasma won't shock you (unless you grasp the work clamp in one hand place your other hand on the metal when you fire the torch). Then you become the path to common, not the metal.
Dealing with EMI and even diagnosing it can be frustrating. Even measuring it takes careful consideration and special equipemnt. In some installs you can violate all of the rules and noting (bad) happens. In other circumstances you have to do everything to stop the problem. The larger and older HF start plasmas can be a real problem. The higher the cut AMPS to more noise there is. even different materials create more noise being cut.


Return to “CNC Plasma Cutters General Forum”

Who is online

Users browsing this forum: No registered users and 6 guests

Easyscriber engrave attachment for Hypertherm torch's