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Grade my cnc plasma grounding

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DMoneyAllstar
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Grade my cnc plasma grounding

Postby DMoneyAllstar » Tue Nov 14, 2017 1:04 pm

I'm trying to "button up" my system and would like to ensure my cnc plasma grounding appears adequate.

When my torch passes over a table slat, some kind of crazy lines flash on my CommandCNC viewer. I figure this can't be "best practice". The PC/cnc/monitor are completely isolated from the table, so it concerns me. Also getting some axis following errors which may or may not be related (addressing separately). Either way I want to close the book on my machine's grounding once & for all.

I've seen grounding diagrams and not all of them are the same, nor are they all as intuitive as I wished.

I'd appreciate some feedback on my setup. Here are the details:

What I'm running:
- DIY 5x10 table with water table (per PPLLC plans), all steel. Table is earth grounded via 8ft long 1/2" copper rod at one corner of the table. #6 wire from floor to table.

- HYP 45XP torch that's on a metal shelf attached to the cnc table. Plugs into a 1ph/220v wall plug circuit on its own breaker. Nothing else on this circuit except the plasma. Ground clamp attaches to the work-piece during cutting.

- CandCNC Linux CommandCNC controller with 620oz steppers. Plugged into UPS.
- Dell PC on Linux. Plugged into same UPS as cnc controller and PC monitor.
(CNC box, PC and monitor are plugged into the UPS; UPS is plugged into the wall on a 20A circuit)

- CNC box, PC, UPS and monitor are all housed in a plastic cabinet sitting on a metal wall shelf 5' from the table with about 12' of cat5 and shielded limit switch wiring from middle of table to the cabinet in 3" conduit.

- 7.5hp 220v compressor on its own circuit in a 5'x5' compressor room outside of shop.

- CNC box, PC, plasma, compressor and lights are all grounded via the common ground at the sub-panel. Sub-panel has its own earth rod. CNC table has its own earth rod (as mentioned above). Both earth rods are on opposite corners of my 25x40 outbuilding.


How would you improve this? Please feel free to be brutally honest, ha.


My machine is cutting great, just trying to button everything up and avoid future issues. Getting busy with jobs and my free time is dwindling.


Many thanks!

Dan

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jimcolt
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Re: Grade my cnc plasma grounding

Postby jimcolt » Tue Nov 14, 2017 1:12 pm

The work cable should be exactly cut to the right length and should be securely bolted to the earth ground rod. The excess length should also be bolted there and bolted to the table as you show. If you want a length of the same cable with a clamp for connecting directly to the plate.....connect this also (securely bolted) to the ground rod. This will direct any stray RF noise directly to the earth ground....which is what it is there for. Everything else is perfect. Jim Colt Hypertherm

DMoneyAllstar
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Re: Grade my cnc plasma grounding

Postby DMoneyAllstar » Tue Nov 14, 2017 1:19 pm

Thanks Jim!

That was fast!! Do you wear a cape with a giant "J" on your chest? If not, you should. ;)

DMoneyAllstar
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Re: Grade my cnc plasma grounding

Postby DMoneyAllstar » Tue Nov 14, 2017 1:23 pm

For clarification...

The ground cable should run from the 45xp to the ground rod and then if I want a work-clamp simply also run it from the ground rod?

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SeanP
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Re: Grade my cnc plasma grounding

Postby SeanP » Tue Nov 14, 2017 2:36 pm

Must be a breath of fresh air for Jim to come on here to a nice post like that after some of the facebook stuff :lol:

I have the lines/ flicker on the monitor when cutting as well, it only happened after moving my monitor to a swivel mount on the table, I think it's from the monitor svga cable running close to the plasma torch cable, it will knock the screen off on a long arc stretch as well, haven't had time to re route the cables, it doesn't give me any cut quality problems.
Powermax 45
Home built table, Candcnc DTHC 2, Dragoncut 620-4
R-Tech 210 Tig, Jasic 250 mig
Sheetcam, Scanything, Coreldraw X8, Solidworks
Table build gallery

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SeanP
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Re: Grade my cnc plasma grounding

Postby SeanP » Tue Nov 14, 2017 2:42 pm

By the way I used to always connect the work clamp to the sheet, but after reading one of Jim's post about no need and just connect to the frame, not had one issue doing this over the last year now, even rusty sheets seem fine.

I had far more trouble forgetting to clip the clamp previously I can tell you :)
Powermax 45
Home built table, Candcnc DTHC 2, Dragoncut 620-4
R-Tech 210 Tig, Jasic 250 mig
Sheetcam, Scanything, Coreldraw X8, Solidworks
Table build gallery

DMoneyAllstar
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Re: Grade my cnc plasma grounding

Postby DMoneyAllstar » Tue Nov 14, 2017 8:32 pm

I got my plasma and table grounds correct per Jim Colts recommendations and ALL IS WELL. No more crazy lines on screen when i blaze over a slat. No stoppages on 2 files about 500 and 1k lines respectively. Going to run a bunch of files tonight before i celebrate.

Being a noob, i screwed up twice. [1] I was using the plasma ground cable in its entire 25' length with it draped over slats, off the table, etc. [2] i was using the plasma ground cable straight from the plasma.

Now the cable runs directly from the plasma to the ground rod. I nixed the work clamp altogether.

DMoneyAllstar
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Re: Grade my cnc plasma grounding

Postby DMoneyAllstar » Tue Nov 14, 2017 10:28 pm

Things ran muuuuuch better tonight. Only stops i had were a handful of z-axis following errors but not during cutting. Would trip the z a couple lines after the M5. Cut 13 pieces of art with minimal issues.

And my LP heater started on the 1st try since being idle since March. Good night in the shop for me!

DMoneyAllstar
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Re: Grade my cnc plasma grounding

Postby DMoneyAllstar » Wed Nov 15, 2017 8:26 am

I think I might also run a ground from my X/Z carriage. It's a big antenna with only 4-points of grounding contact (the v-rollers). Assuming this will get rid of the noise that's impacting my Z-signals and further clean up noise for the X & Y.

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larrycameron44
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Re: Grade my cnc plasma grounding

Postby larrycameron44 » Thu Nov 16, 2017 1:16 pm

jimcolt wrote:The work cable should be exactly cut to the right length and should be securely bolted to the earth ground rod. The excess length should also be bolted there and bolted to the table as you show. If you want a length of the same cable with a clamp for connecting directly to the plate.....connect this also (securely bolted) to the ground rod. This will direct any stray RF noise directly to the earth ground....which is what it is there for. Everything else is perfect. Jim Colt Hypertherm



What is the exact correct length required for a earth/ ground cable?
I have a Hypertherm powermax 45 Torchmate 2x4 system and just connect the earth clamp from the powermax to the plate....... for the last 6 years. Do I need to have a earth rod and do all this?
Larry Cameron
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DMoneyAllstar
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Joined: Tue Jan 17, 2017 9:11 pm

Re: Grade my cnc plasma grounding

Postby DMoneyAllstar » Thu Nov 16, 2017 3:25 pm

I would say "exact length" means...
...no coils of wire, no excess, etc.
...simply from the plasma to the rod and nothing more.


Bought some 8ga stranded wire and some a better ground rod strap (had the 1-pc 1-bolt one, now going to use the 2-jaw 3-bolt bronze one) for my gantry grounding. $35 to see if it helps any. Also have an extra / different mouse and keyboard simply to "check the box". Hoping to get it done tonight and tested on a couple files.

Billy wesson
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Re: Grade my cnc plasma grounding

Postby Billy wesson » Thu Nov 23, 2017 3:41 pm

You may also add two more earth ground rods three feet apart string them together and add a small box of rock salt to the dirt this will bond the rods to the earth your goal is 2 ohms or less at the table good luck this worked for me we have a heavy clay soil here but it did the trick


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