Homemade, cheap, plasma CNC

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12 May 2021 12:27 - 12 May 2021 12:30 #208617 by RNJFAB
Replied by RNJFAB on topic Homemade, cheap, plasma CNC
oh, the saga continues.

Yesterday managed to dial in the settings with some help for the thc. all cutting great, good height control, great lead in and out.
According to the statistics page I have over 200m of cutting and 1000's of pierces.

THEN ...................
nothing, no spark, check power to plasma - fine, power to MESA - fine, change nozzle - fine, still nothing,

The mesa output led seams dim compared to the other lights (input led's), but it still comes on and off like it should, replace relay and all wiring to plasma, still nothing. Give up for the night.

Tonight back at it trying to get it going. redo all the wiring again, change to output 2, change relay, double check everything from pictures of setup that worked, double check all MESA manual setup, etc.

NOTHING...........

Thinking there may be something wrong with he outputs I go all the way to output 5. change settings in the HAL. check to ensure the right output is firing, connect everything, test, BAM it's all working, torch fires as requested. SWEET.

Start to cut, first holes cut, second hole cut, third hole - torch doesn't fire. FFS. check in the control panel to find that the LED for output 5 doesn't light up when I activate the torch. BUGGER. upon closer inspection output 4 and 3 led's are glowing.

Just a random guess, but, I think the outputs may be fried, another MESA board gone. actually lost for words right now.

any suggestions?

Connection for relay


dim output 1


relay


dim outputs on 4 & 3 I think
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Last edit: 12 May 2021 12:30 by RNJFAB.

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12 May 2021 13:15 #208622 by PCW
Replied by PCW on topic Homemade, cheap, plasma CNC
If 7I96 outputs are being damaged, it suggests a major EMI, ESD or grounding issue

I would at the minimum:

Mount the control electronics in a grounded metal case

Ground the 7I96's frame ground connection to this case.

If your plamsa source is not designed for CNC use, feed
any control wires from the the plasma through a RF filter
(this may be as simple as a 0.01 uF 500V capacitor to frame ground)

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13 May 2021 08:48 #208716 by RNJFAB
Replied by RNJFAB on topic Homemade, cheap, plasma CNC
Thanks PCW,

everything is in a shielded metal box that is part of the frame.

7I96 is mounted to the din rail, grounded.

currently no RF filter for plasma control wires.

As mentioned before this setup has done hundreds of meters of cutting with thousands of pierces, with no issues.

Really would like to know what has caused this so I'm not forking out more $$$ on another MESA board only to have it fail in another 3 weeks.

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13 May 2021 22:36 - 13 May 2021 22:37 #208764 by PCW
Replied by PCW on topic Homemade, cheap, plasma CNC
As I explained in the other thread, the Cut 50 plasma source is a HF start
device, these generate massive amounts of EMI when starting the torch.
At least some of these have a spark-gap HF source, basically a Tesla coil...

HF start generates so much EMI that in general HF start plasma devices
are not recommended for CNC use at all. To use them requires very careful
shielding and grounding and keeping all wires from the plasma cutter far way
from any signal wires.
Last edit: 13 May 2021 22:37 by PCW.
The following user(s) said Thank You: snowgoer540, RNJFAB

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16 May 2021 07:51 #209051 by RNJFAB
Replied by RNJFAB on topic Homemade, cheap, plasma CNC
Thanks PCW,

I experienced this with the first version (no shielded cables) so I ended up using Alfoil (yes from the kitchen) to wrap all the cables and the control box. It worked and all was sweet, even if it did look like some crack pot was trying to stop the aliens from steeling my data.

Now the plasma is at one end of the cnc and the signal wires are at the other. The main box is steel and sealed. All cables are shielded and all joints are shielded as well. Haven’t noticed any interference since completing this stage.

Looking at the plasma upgrade now, just waiting on some quotes. Gotp p bit of time as it will be a while before the new Mesa board arrives from the states.

Cheers

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19 May 2021 14:00 - 19 May 2021 14:01 #209512 by RNJFAB
Replied by RNJFAB on topic Homemade, cheap, plasma CNC
Ended up getting a unimig cut 45 plasma.

Now to wait for the new board then I can get it all cranking again.

If anyone has hooked one of these up please let me know,
Last edit: 19 May 2021 14:01 by RNJFAB.

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24 May 2021 09:31 #210043 by RNJFAB
Replied by RNJFAB on topic Homemade, cheap, plasma CNC
OK, new MESA 7i96 board has arrived. New UNIMIG Cut45 is in place. checked the resistors in the plasma to get 20:1 divider ratio to suit the MESA THCAD10.

Final connections tonight from the plasma to the SSR relay (for torch firing), Arc OK input on MESA board, IN+ and IN- to the THCAD.

maybe I'll get brave and try and get some cutting happening.

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02 Jun 2021 04:11 #210936 by RNJFAB
Replied by RNJFAB on topic Homemade, cheap, plasma CNC
It's alive again.

Totally different cut quality between the $200 Chinese plasma and the unimig.

THC through the MESA THCAD10 is amazing.

Only glitch so far has been arcok signal lost (often at the end of a cut) that I then have to override (ignore arcok) to get it to continue. If I leave the ignore arc ok on it doesn't get a proper pierce before moving on.

I'll try and get some more cutting done this weekend and post some pics of old v new cut quality.

Cheers

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02 Jun 2021 09:19 #210980 by tommylight
What version of LinuxCNC?
The arc lost at the end of the cut was fixed quite a while back, so an update should get that fixed.

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10 Jun 2021 12:21 #211691 by RNJFAB
Replied by RNJFAB on topic Homemade, cheap, plasma CNC
Thanks Tommy,

Running AXIS 2.8.0.

Computer is a box in the shed so no internet to it.
I'll try and get an updated version and load it onto a usb.

I'm hoping that in a few weeks i'll be able to get QTPLASMAC onto it and step it up a bit.

Cheers
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