Commissioning a new DIY plasma machine

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Les Newell
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Re: Commissioning a new DIY plasma machine

Post by Les Newell »

Pilot arc allows the arc to strike and maintain with the torch away from the surface. HF strikes the arc.
When I talked about the screens I meant that they should only be earthed at the box and not connected to the frame anywhere else.
Not sure how I can isolate the earth leads though, because the power input earth is shared with both the plasma machine and the power input for the electronics through the mains supply.
The shared mains earth should not be a problem. Basically you don't want the earths to form a loop anywhere. If the screens touch the frame you have a loop: mains earth->control box->screen->frame->mains earth
Looking at your photo it looks like you are using connectors with metal shells on the control box. This is good - your screen should connect to the metal shell of the plug and socket should have a good electrical connection to the box (scrape off the paint around the fixing screws to be sure).
regpye
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Re: Commissioning a new DIY plasma machine

Post by regpye »

Thanks Les, I was a bit confused with your earlier post.
Yes the shields I have only connected at the box end and the mounting plate that holds all the aircraft connectors is metal and connected to the box too. The other ends of all the cables have the shields cut off close to the end and is not connected, so it will not be making contact with the frame.
The only cable that is not shielded is the trigger cable, maybe I should replace that one to be sure.
I downloaded a paper from the net by Hypertherm that talks about this problem and will try to follow what is suggested and keep in mind what you have said also.

As for the arc, I can press the trigger and maintain a steady arc when nowhere near the metal surface.
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regpye
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Re: Commissioning a new DIY plasma machine

Post by regpye »

Well I don't know what to try next.
I have fitted all the earthing as described in the above diagram. Fitted shielded cables everywhere and only attached the shield at the control box end, other end free and not touching the earthed frame. I have fitted several ferrite suppressors and also fitted a EMI filter on the mains coming in to the control box.
I have tried without the limits being plugged in to see if the problem was coming from there and I also disconnected the probe as well.
All the stepper motors are wired with shielded cable.
The machine works 100% until I turn on the plasma, as soon as the trigger activates the processor shuts down at the first spark. I can run through a complete part in simulation mode, by having the plasma turned off, but as soon as I try to make a cut everything comes to a halt and I have to reset the processor and clear the alarm.
I think I will have a sleep on it and see what I can come up with tomorrow. I know others have been successful running GRBL and UGCS, so there must be something that I am missing, could be the plasma machine itself.
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Les Newell
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Re: Commissioning a new DIY plasma machine

Post by Les Newell »

Is the controller connected to your computer via USB? If so the HF could be getting onto the USB cable and from there taking out the controller. Can you try running it off an SD card?
regpye
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Re: Commissioning a new DIY plasma machine

Post by regpye »

Thanks again Les,
Yes I came to the same conclusion, could be the USB cable.
Not able to run off and SD card unfortunately, I would like that.
After doing some research I found this info that may be the cure I am looking for, I have ordered the parts and will have to wait until they arrive before testing further.
https://youtu.be/k3Q9S1hKPQc
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Les Newell
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Re: Commissioning a new DIY plasma machine

Post by Les Newell »

I've had pretty good success using ferrite toroids for noise control, e.g https://www.ebay.co.uk/itm/10X-36mm-Out ... 3172882761. Wind the cable through the toroid 5 or more turns. This gives more aggressive filtering than clip on ferrites. With a USB cable you'll probably run out of space before you get 5 turns so you'll have to just fit as many as you can.

I generally end up fitting ferrites to reduce outgoing noise from drives but they work just as well to stop incoming noise.
regpye
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Re: Commissioning a new DIY plasma machine

Post by regpye »

Les Newell wrote: Wed Jan 15, 2020 11:08 am I've had pretty good success using ferrite toroids for noise control
Thanks Les,
I am waiting on a set of different sizes coming next Monday. I have used all I had in stock, but didn't have any that would fit the USB cable inside the control box. I am hoping that will sort the problem out.
I will also try using LaserGRBL instead of UGCS. I have been using LaserGRBL with my DIY laser engraver for a few years now and it is very good and I don't see why I couldn't use it for sending out sheetcam code to my machine.
regpye
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Re: Commissioning a new DIY plasma machine

Post by regpye »

This morning I disconnected the plasma machine from the CNC table.
I ran a small sheetcam file to test the CNC table and it all worked fine without any problems. (no plasma connected)
The plasma machine was on the opposite side of the room, so I ran the program again and while it was running I manually used the plasma cutter away from the CNC table, and the same thing happened, the CNC froze as soon as the pilot arc started. There must be a lot of EMI radiating from that plasma cutter to do that.
The plasma cutter is advertised as CNC compatible, but in no way can that be true for it to act like this.
I think I have done my money on this Chinese machine, it was not a good buy to have these problems.
Dott
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Re: Commissioning a new DIY plasma machine

Post by Dott »

regpye wrote: Sat Jan 18, 2020 11:35 pm I think I have done my money on this Chinese machine, it was not a good buy to have these problems.
These machines aren't made well for CNC tables as you are finding out but they can be used. It takes extra care and planning when wiring the table to mitigate EMI issues. I'm currently working on my first CNC table using a Colossal Tech Cut50DF. It too is a pilot arc machine but uses HF in conjunction with the pilot arc to start cutting. I'm still working through some bugs but as of now it will cut simple parts.

My EMI issues came up as a triggered E-Stop. Reviewing forums I found that rewiring the E-Stop to trigger on pull down instead of pull up fixed my issues. I still have trouble with my laptop touch pad locking up but the table seems to run ok. Now I need to figure out how to get the torch to turn off after the cut is made.

On another note These Cut50 plasma units aren't that bad. The torches and consumables are junk so plan on buying a bunch. As mentioned before they aren't the easiest to get running on a CNC table but it can be done.
Zikken Eric
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Re: Commissioning a new DIY plasma machine

Post by Zikken Eric »

Yo down under - welcome to the jungle!
I´m building a DIY cnc plasma like yourself, and will use a cut50 - now you´re ahead of me since we write 2021 - what is the story?
(I might have some tips or tricks, but for sure questions for you - so - are you still here?)

/jens-erik
regpye
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Re: Commissioning a new DIY plasma machine

Post by regpye »

Yeah, I am still here.
I haven't used the plasma for a while, but I got it going except I was not able to have the limits working in any form whatever.
I could initiate the limits and they would work fine right up until I fired the plasma, then everything froze.
I ended up disconnecting the limits and I also had to turn off the limits in the GRBL settings as well to get the machine to work with the plasma.
I would start the machine up and set a zero point manually and then all went well.
The plasma cutter I ended up using has a low frequency pilot arc and a video of the first cuts can be seen here https://youtu.be/FAIyzK6thnI
Killer
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Re: Commissioning a new DIY plasma machine

Post by Killer »

Seems like a path similar to what I'm experiencing, did you have any success, basically my controller seems to work ok without the limit switches enabled and when I light up the torch my monitor flickers of turns off, switching from a vga cable to a dvi cable has helped a little with this but I plan on getting a longer earth clamp (5m) (already have a longer pencil torch lead 7m) and putting the unit away from everything, at first I thought it would be the torch causing the noise but my tests don't support that theory so going to try a longer lead.

Will also be using screen cables as I used just normal single core as like you I thought I was buying a low frequency machine, the ebay seller has confirmed that it is a LF machine but I think there is a bit of poetic license being used here in the fact it might just be a lower frequency that the older versions, still HF but lower :)

Will also be using ferrite cores or beads everywhere I can think of.

If you found the magic bullet I'd certainly be interested in hearing more :)

Take care

Rich (Perth WA)
regpye
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Re: Commissioning a new DIY plasma machine

Post by regpye »

I have been out of commission personally for a while, still learning to walk again after a medical episode and being given the wrong drug by the hospital.
Since my last post, I have changed the machine a lot. I have now installed a new system for the Z axis, one that uses a self contained lifter and THC.
I also have changed over to using Mach3 software. I have the machine running OK, but not been able to do any test cuts yet due to health issues, but all looks like it will be a better move than my previous build.
The lifter I built myself and it uses a 24 volt DC geared motor for the lifting, the controller for the lifter I bought from China which also comes with a voltage divider. The THC will work on any plasma machine and doesn't need a Z axis as it does all the Z movement within the lifter mechanism.
The THC system used is a SF-HC25K. I got most of the information on setting it up from a youtube channel Minh's Man Cave. The lifter I have designed and built using my CNC mill and also my 3D printer. It has a built-in floating head and up and down limit switches.
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