AddenDUMB: I Broke My CNC Plasma Table! | Learn from my mistake | Langmuir Crossfire THC 

SAFETY NOTE: I do not recommend disconnecting any safety grounds. The connections that I isolated were connections between the plasma table frame and the earth ground that I inadvertently added to the system with my modifications. The plasma cutter, CNC electronics, computer, monitor, and plug strip are all still grounded to the safety (protective earth) ground through their power cords, as they came from the factory. I am aware that there are various documents recommending that plasma tables should be separately grounded. The Crossfire plasma table does not come from the factory with provisions or instructions to earth the table frame, and in fact doing so prevents the torch height control (THC) electronics from reading the arc voltage. If you are concerned about this, I'd love to hear about it in the comments, but I can't do anything about that design, as it is inherent to the Crossfire THC.

Telling the internet you did something wrong. Oh i'm putting on the popcorn and coming back to the comment section! Thanks for sharing and educating those open for that sort of thing..

As soon as you mentioned you went back to the carbon-reinforced materials, I had the concern that carbon fiber is a quite decent conductor. Evidently, the level of integration in your feed material, it's density, and discontinuous orientation of the cut strand is isolated enough that you didn't form a circuit with your part. Again the carbon version, like the metal is NOT necessarily - "more better". Running a composites shop, we are extraordinarily careful to keep fiber strands and dust out of the air as they eventually and inevitably find the magnetic fields of circuits and create shorts. Plain plastic is definitely more predictable isolation. ceramic, phenolic or even end-grain oak can provide modulus if you need them:)

Well you ironed that out really quickly. And I thought I was the only person who could improve things so much that they stopped working.

Great find and troubleshooting. Hopefully no damage will pop-up later. Thanks for sharing the "Lessons Learned", hopefully it will help the rest of us not over look these small details.

Merry Christmas, glad you solved your problem, no harm, no foul. A while ago, I fried my multimeter while diagnosing a plasma cutter; I mistakenly connected my volt meter to the high voltage output.⚡

As a retired healthcare professional, kudos for your excellent application of diagnostic process.

Solid find and fix James! Thanks for sharing.

Ah, it's the little things. Thank you for sharing this piece of your process!

Great troubleshooting James - thanks so much for showing us the problem and solution! Merry Christmas

"What kind of things have you screwed up by trying to be clever"... might be the best question I've heard all year😆. Great vid as usual James!

finally got lined out on my plasma cutter i have been 3 weeks, burnt up one vim box and your videos saved me. i was ready to give up and sell my machine.

Merry Christmas to you and family James. A year ago I built my own 3-axis Mach3 control cabinet and also built my own Z-axis for implementing THC on the Crossfire. In doing so, it encountered the same grounding issue, but in the form of crippling EMI at the controller. Once the box was isolated, problem solved.

Mistakes the world’s greatest teacher . Thank you for teaching us through your mistake.

Thanks for sharing the mistakes, I think I learn more by seeing them and it also helps reinforce the fact that people in videos are actually humans that make mistakes just like the rest of us 😁

Merry Christmas, James & family! Nicely done diagnosis, too. I doubt it would ever cause problems after your fix, but you might want to insulate that mount at the monitor. The water in the tank probably gets conductive between cleanings, and that monitor stalk looks pretty close to ground. 73 de W4YBO

A nice, simple fix to close out 2021 😊. Happy New Year, James! 🥳 Cheers!

Excellent tip. I should be getting the THC upgrade to my older CrossFire in a few days and I'll try not to repeat your mistake. Merry Christmas. Ciao, Marco.

Not that I’ll ever own one of these, I’ve been a very long time retired however, a video well done sir, and thank you, I enjoyed watching it and learn something

Just found out I have a McMaster-Carr in Atlanta and its only a 30 min drive for pick up. Thanks for introducing them to me. They are awesome!

A useful gotcha to be aware of. Thanks for sharing

As soon as you started describing the problem my brain went, the vesa mount screws! You just solved the problem higher in the chain. Very nice, thanks for sharing, and like you I am impressed nothing broke. Given how I haven't seen any signs that say "do not ground" on the metal frame, I'm a little surprised the box doesn't do a similar continuity test on startup. (I'd be curious how good the isolation is that you have now: what at least the British call a "Megger" - for measuring mega-ohms resistance vs thousands of volts, which is part of at least their workplace electrical safety routine testing - would be an interesting test, since the voltage used for continuity checks is pretty low.)

I can see how this is easily overlooked, I guarantee you’re not alone on this one James!

Great review of ground loop issues

Yep- I have done that and sometimes it even makes cool smoke!

thank you so much really appreciate the video having the same issue, hopefully it's the same fix

Metal is more better has been my musical philosophy for 30 years 🤘🤘🤘. Great video as usual James

Nice Christmas gift of advice from a bit of honest self-criticism. Thanks!

thank you for an honest post

It's always interesting to see what sort of signals people put through the chassis. I've been rebuilding a cheap 3D printer that suspiciously tied the logic board to the frame, but fortunately it appears that was just a "safety" ground. (Note that the printer takes 19VDC in, and no grounding, so it's not earth ground.) The nozzle, thermistor, heater cartridge, and bed heater never connect to the chassis ground, so nothing ends up being mysteriously polarized, fortunately. (You have to check, because if one end of the heater ends up connected to the case and that end happened to be wired to the control board's positive terminal, then you blow a fuse, which is annoying. But, luckily they isolated everything, so it wasn't a problem.)

Thanks for this video !!!

At first I thought you were going to say that the grounding issue fried the computer. That would have surprised me somewhat since industrial computers are more resilient than the consumer PC, but there is always that one instance where something goes south and the magic smoke leaves never to return again. I am sure that this video will help people well into the future.

No harm…no foul…good discussion

Not a big one but today I was finishing mounting a DRO to my drill press (long project) and after several hours work I turned on the display, moved the axis, but the reading didn’t change. I was worried I had damaged something during the installation. Eventually I realised I had not plugged it into the display! All working fine now.

Merry Christmas

My current project had a similar issue with a USB connector and a touch screen. The entire aluminum frame and enclosure is connected to mains ground. Turns out the OEM touch screen mounting pads were connected to the electronics ground which in turn meant the electronics ground was connected to mains ground. Had to use plastic mounting screws and washers to isolate it. Next was to make a custom USB enclosure surround to keep the USB ground from touching the case. No damage from being grounded but testing with the meter was kinda baffling at the start.

It seems at least one other person has spotted the same issue I did. My youngest brother is the senior electrical engineer at a top F1 team and been there for 27 years! The problems he has experienced and had to resolve due to carbon fibre composite conductivity are many and varied. Without going into great detail I should advise anyone thinking of using ANY form of carbon composite material to consider fully and test experimentally any possible issues that may occur. An example of one "trivial" decision such as to cut two separate holes to pass high current cables through a carbon fibre sheet rather one much larger hole is the potential for LARGE eddy currents WITHIN the carbon fibre to occur (just as in a steel sheet) & generate a LOT of unintended & unexpected heat and even fire. James, you may be lucky with the carbon filament you have used but it MAY just be that there is NOT full isolation but sufficiently high resistivity to "isolate" the problem. A proper high voltage isolation resistance test from a tame sparky might be wise as a precaution.

Great info

The ground gremlin strikes again - thank goodness it didn’t damage anything. At first glance, I thought you had epoxied your hand to your forehead - hate it when that happens 😀. Really like the subjects you cover.

It might be a good idea to relocate the monitor location so you could stitch a larger than the table size on your table utilizing the open end of the table. That is one advantage to the smaller table, I have hard mounted my power strip, the water pump and have my plasma cutter seated on a welded on frame tray. Nice to know I have work to do.

When I was a noob at electronic, I was so confused seeing the starter of my car having a single wire. I was like how the starter is working with a single wire. I didn't know the hole car body was the ground. :)

repeating Mathieu B, I would use something other than the carbon fiber petg, it is not conducting now, but I think you maybe lucky, and wear and tear may eventually make electrical contact.

It's a matter of remembering where your wires are - and the fact the table is one of them !

thank you for this video

A video out of a couple of plastic washers? 8) still you are good at it and happy 😁

I wish to you and your family Merry Christmas.

Well, I'm just glad nothing expensive got baked on you in the process. I think we all have some ideas that turned out not so great in the long run, lol, we're all human.

Ground isolation is always a challenge. One thing that is easy to overlook when using PC peripherals is the connector housings. USB, HDMI etc connectors are tied to chassis ground within most devices. Easiest way to check is to measure continuity from AC input ground to connector housing. If no continuity is measured, plug in a regular USB drive and recheck. Some USB peripherals do not isolate signal and chassis ground.

Love all the haters out there. I made a silly mistake with my table this summer.... I set an exhaust manifold on it to weld a broken bolt. This resulted in damaging the transistor on the motion control board for torch fire control. Didn't know I did until months later making Christmas presents. Guys at Langmuir helped diagnose and really took care of me. I love my little crossfire. Only wish I bought the pro for size!

As others also stated… watch out for the conductivity of CF-reinforced filament. Depending on print settings it can become conductive. If i remember our tests correctly, the conductivity of the 3dxtech CF-Petg increases with print temperature. Stratasys CF-reinforced filament prints ARE conductive to a higher degree… i would replace these CF parts for pure plastic, to avoid indeterministic future issues. ( I would not trust the parts to keep their high impedance when exposing them to transient voltages, as the plastic so easily can alter its behaviour due to print settings.) That said… i am a heavy user of 3dxtech esd-petg for electronic projects… as normal petg generates quite big levels of electro static voltages when breaking them free from the metallic build plate of the Prusas we use.

I fried the PCM on one of my customers Jeep once. I was using a Power Probe Hook to test a crank sensor and needed both hands to place the leads. I had wedged the probe between the heater hoses so I could see the screen. I had a coworker start the engine. As engine started, it shook the heater hoses and depressed the voltage button. It sent 12V to the PCM via the signal wire. $800 later, I learned to never use a Power Probe to check for sensor signal.

Happy christmas, and i din't know that earth thing thanks for the warning🎄🎇✨👍😎

One thought: the printed sleeves; do they contain considreable amount of carbon fiber ? Carbon fiber is conductive in tself, so you might need to keep an eye how this evolves. Personally I would have used PE for the sleeves as enything containing carbon fiber can easily be conductive.

So proud of your honesty and willingness to share ... I am living proof that dumb mistakes only get worse as your age increases ... sorry ... But maybe you will break the trend... Thanks for Sharing ... Stay Safe and Merry Christmas ...

Hopefully it didn't fry anything... Just in case something (some sheet or else you are cutting) goes shorting the table to the post (which isn't far), I would insulate the monitor from the post (opening the holes in the mount and adding some plastic spacers should do the trick) Don't bother making mistakes! Sure you learn things but we do too :) even more when you make the mistakes before we have the chance ;)

I'm about to add THC to my crossfire. Thanks for the heads-up. I'd much rather avoid a problem than spend a day diagnosing it as I pull out my hair.

"because Metal is more better" 6:34 yep, generally true... electrical isolation can be a pain though.

James obviously "solved" his problem, but this video provokes more questions than it answers! Part of the confusion appears to be between electronics signal ground versus chassis safety ground and the implications of connecting the chassis ground of the control box to the chassis ground of the table. In principle, no arrangement of interconnected grounds should cause the plasma voltage detect signal to get shorted and read zero... unless.... OK, so the plasma table is basically a positive-ground system -- that is the table carries the positive side of the plasma power, and the torch voltage (to be measured) is negative relative to that. And yet Langmuir's detection interface "Voltage Input Module" (VIM) appears to consist of a simple voltage divider, possibly with some filtering. If it has no active component, then it will produce a negative output voltage (relative to the table). But that would require the Torch Height Controller board to accept and digitize a negative input voltage, which most analog-to-digital converters will not do. That could be easily solved with an inverting op amp circuit on that control board -- but is that what Langmuir implemented? The alternative would be to float the electronics and attach the electronics signal ground to the negative output wire from the VIM, and feed the VIM positive output (ie: possibly the table frame) to the ADC positive input. If _that_ is how it's implemented, then of course an unanticipated connection of the electronics ground to the plasma table will short the VIM output signal, and make the TH control board see zero for the plasma voltage. That would be a very poor design, so I don't want to jump to conclusions, even though it explains the symptoms. It would be super interesting if James would measure the signals from the VIM to the TH controller, and determine what their voltages relative to the table, and relative to electronics ground! Meanwhile, judging by forum posts, some owners of this gear have other problems relating to noise propagation of one sort or another disrupting the controller MCU(s?) and/or comms with the PC. These may entail grounding or shielding issues, but are not the same as the controller running fine but seeing a zero plasma voltage. Further, connection of industrial gear to a PC over USB is a known issue in general, and greatly eased by providing an isolated USB port, at the cost of a ~$1 part, (though supply of those has dried up during the chip shortage).

Well... I am glad I watched this .. lol I was wondering why I need plastic washers for .

Suggestions for your plasma table from experience with mine. Put it in a separate room and/or build a downdraft vacuum system to evacuate the particulate while cutting. Even with the downdraft you WILL get top spray that will accumulate in your shop unless you set a vacuum nozzle at the cutting tip. For best results put it in a separate room and build a downdraft for it. Just saying. Enjoy your videos

This looks like a nightmare to find the short, but fortunately you didn't break the controller with this high voltage. I once connected 20V to USB data through a faulty stepper driver and it broke a few USBs on the motherboard and the computer has some trouble booting now

Nice. Any chance on sharing the G-Code for the spacer?

Deductive sleuthing at its best !!! And how do I fix it with innovative reasoning. Good Job......

2- things i need to know from you.. your powermax 30xp, have you cut aluminum with it and what is the max thick you have cut with it (any material) ..?

I'm really curious now if that did in fact fix the problem because our plasma table at work (which has THC too) has the controller box grounded though the table and through the ground pole of the power plug. One thing to note though that might be a factor here is that per the manufactures instructions, our table is directly grounded to earth via 10ft of ground rod driven into the ground next to one of the legs of the table and its connected to the ground connection point on the table where the plasma work clamp ground connects. I know that there was a note in the install instructions that said that without that true earth ground, there will problems with erratic THC control behavior.

Whilst this is working the use of carbon fibre reinforced plastic raises a little concern for me. Makin the sleeves with a conductive element seems like a risk for some future hard to debug issue. I've not done any work with that material yet in 3d printing, mostly know it in terms of electrolysis risk in composite form where the structure is quite different.

Carbon fiber is a great conductor!

I skipped checking all corners on a cut and over an empty space, the THC started diving. Coulda been bad but the empty space wasn't that big.

Any issues with the carbon fiber making the sleeves somewhat conductive?

Hi James there is not enough lines on you tube to list all the screw up's I have made in my life time but that one is a very easy one to do and yes I have done it not on a plasma table as I don't have one, but it can happen on many different machines that have a computer attached. Often it is allot harder to track down probably why I don't have any hair left.

I noticed you are using a 30xp and the thc upgrade. I am using the same table and cutter. I purchased the thc upgrade but I am not sure how to hook it up inside the 30xp any tips? Specifically what color wires to hook to.

ah, yes, the goods old ground through a data cable. Learned that one the hard way on my first project at my first job. We made a data capture box for Buses (that they could plug in to the bus PLC, capture acceleration/deceleration/speed to analyse driver performance), spent 4 months on it, worked flawlessly. we deliver it to the customer, they come back saying it didn't work. We try it, it works, ok, check all the cables, everything is fine. I go, with my boss to their office, we plug it in, it doesn't work. I get my laptop out, it works. raaaah. turns out, their laptop power bricks passed ground over to the positive pin to the computer. When plugging in the serial port, while the capture box was connected, the ground from the db9 between computer and plc would create a ground loop and crash the electronics.... that was a fun one.

Did I understand correctly, that the nuts in the monitor's VESA mount are connected to the monitor's ground? Then I would rather recommend to isolate the monitor's VESA mount from your monitor stand, instead. As it is now, a larger sheet of metal could easily short between the vertical bar of the stand and the table.

How long did it take to chase that down? Myself, I'd have pulled most of my hair out before finding that issue.

I have a similar problem, maybe you can help. When I check continuity from the USB to machine frame It show continuity, only when the Plasma cutter is plugged into the DIV input. Do you know what would cause this. any help would be appreciated.

do you think the manufacturer could feed the height voltage through an isolating adc/comparator ? instead of simply feeding it to the control box, which is the root of the problem ... afaik

dude , you're a fabricational rock star ...

High frequency of plasma unit can be pretty bad on electronics. Good thing you didn't fried anything because sometimes it does that to boards....

Shit. A ground loop the long way.... During university courses in electronics and measurements we learned about ground/earth free measurement situations, and the cautions. . Why a screen, computer would be have chassis to ground/earth? Poor design I would say. Pooh, nothing got damaged. Very nice to hear. You were lucky having equipment that just shut down. It's nice to deal with electrical stuff being "fully isolated" meaning having to protective ground/earth... To Your final words.... In the end of the 1970:ies we built hobby computers, Z80, Texas 9900 etc. One hard thing was to get a monitor. Some guys used televisions and they had the chassis connected to one of the two mains pins..... That called for turning the mains plug to the right position to get the chassis connected to the neutral......

Any reason you went with the Avid CNC router instead of the Langmuir mr-1 ?

But, but, but, surely CF PETG is also conductive to some extent? Did you measure with the resistance setting, instead of the continuity test of the meter? My Fluke has a threshold for continuity, which still shows reduced resistance, but does not always trigger the continuity signal. But then again, you know what you're doing...

Curious what the resistance is of the Carbon printed parts.

Great Info. Thanks very much. Did you really say that metal is "more better"? LOL Just had to give you a bad time.

This is a bit confusing. If what you say is true this means in operation anything connected to the return lead of the torch is not at ground potential. This sounds potentially dangerous. I think the problem really is related to the way the torch height voltage is measured. Got to look at how my torch is wired tomorrow. Planning on mounting my plasma torch to my CNC router table.

Well, building the ELS, mixing 2 projects on the workbench and connecting 25V DC to the circuitboard instead of to the servo. Which fried the logic board, the Clough42 driver board, the rotary encoder and the display circuit board. Nice going, expensive mistake, and smelly

Ground loops can really be a pita to solve. Nice work!

Finding those kind off short circuits in elevators always make you rethink your capabilities.

Isn’t carbon fiber typically conductive?

It is interesting since most pro level tables ground the enclosure to everything through star grounding. Hypertherm has a 12 page manual in proper “star” grounding of everything so does Lincoln. All main plasma systems call for a single busbar to each individual component including Cabinet, gantry and the Z to an earth ground/ Rod! It’s common to ground all these points then run it to a wall ground. Langmuir machines are a horrible quality product. They don’t use ANY (absolutely no) double shielded cable or drains and in fact.. they use standard printer cable with no db9 pas through EMI filters. The noise issue is exactly why they don’t implement safety products like limit/ home switches or e stops. They don’t use any ferrites They split wire all power lines, coms and grounds! They use no busbars or distribution blocks! They use all (too long) 22 gauge non silicon wire with agin no shielding or ferrites between the controller and the cheep $10 Chinese drivers. The don’t use proper terminals or ferrules, they just tin the wire! (Even in the PS! They use cheep, unbranded and “Noisy” power supplies! They use usb power to power the 5v and 24v lines of their older Chinese boards....pre Arduino uno board. They shipped units with improperly rated torch relays for months! The original relay was also inadequate! They don’t coat the control box in EMI/EMF protective coatings. They inadequate ground the entire machine. They use extremely cheep stepper motors. They use undersized ball screws that whip like it’s a hurricane and many times arrive bent. They use no preload bearings/nut on the ends. They use cheep backlash nuts. They use non EMI filtering AC panels mounts. They use extremely cheep panel connectors know to arc, rot, crack, and melt with no ability to drain EMI! They have customers use T-splice connectors on their plasma cutters. Their marketing is the only thing they do well...like no other cnc plasma company that came before. They have a business model that sells inadequate products then UP sells continuous UPGRADES to its consumer base. Their forums are filled with idiots who’ve completely rebuilt their machine many times over but are still loyal to the brand like a cult. They used to falsely claim that their linear bearing system was proprietary but wasn’t. Their water pans / water table can’t even fully drain, yet they know this, still produce it the same and suggest that each and every customer modify their own pan. They white labeled “fire control” and utilized open sourced projects for their THC and main board firmware. I was extremely disappointed to when you started pushing their machine. You know quality components and engineering! How many sub par machines do you think your channel sold? You fully comprehend EMI protection. You know the value of these sub par components don’t justify the MSRP if a 2x2 2 axis machine. Your peddling junk. There are serious quality control issues with this brand! n in arguable fact.

I spotted a multimeter that I also own

How did all of us genius-tell you what you’re doing wrong, know it all’s, not see this coming?!?

I would have thought the plasma cutter voltage would have had a full isolation measurement.

USB ground is connected to earth ground through the monitor?

And I thought you were going to show us a Fusion add-on for Pareto Analysis… maybe next time? Two givens for my projects> 1. Its always Something… 2. And usually not exotic.

James Marry Xmas to and the Family. On my plasma system I put the work clamp to the sheet that I am cutting I did the table thing and get ark spikes that would shut the computer off it was isolated system I seen my friend system in his shop and ask him about how he was connected the work clamp to the steel directly and then he said the spikes would reset or shut down his computer. The light bulb 💡 on yaaaaa since then my table been running flawless for 10 years.

Carbon is conductive too. Not a good conductor but conductive none the less.

When I was very very young my parents had some decorative candles for the Christmas tree. And, in my mind, candles should burn, no? Otherwise they wouldn't be candles. So I "fixed" my parents' mistake... And then I couldn't sit right for a week...

Seems that Langmuir has made a poor choice by not providing isolation for the torch height circuit. Mesa (common hardware supplier with linuxCNC) has a fully isolated THC input board which eliminates this issue for systems using their hardware. Thanks for confirming that it is better to build and know what you have than trust others to design safe and robust systems.

Oho so sad 😔

What's the model of the Asus touchscreen?