Cheap THC

for the Cut 40

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November 2016 was the beginning of the start process for my cheap THC.  Are you getting the trend here, Cheap plasma cutter, CNC on the cheap etc.  Again a lot of quips about wasting my time, should be buying this, that or the other.  I had been looking at voltage comparators on the Internet and settled on a 4 Channel Voltage comparator found on Ebay, it came in at less than £10 (UKP).  So I ordered two.

Here is a picture of the board I decided to use:


It provides 4 channels, has positive and negative inputs, works up to 32 Volts and take 12 Volts DC power supply input.  Watch out you do not get the 5 Volt units as they seem to be made to be only to monitor up to 5 volts.  The downside is these uses relays, so may be a bit slow on switching. (actually found the data sheet on the relays and they act in a maximum time of 10 mS). But as I believe Mach3 monitors the THC inputs every 100mS, (hard to find any true information on this), then relays seem to be good enough until they fail.

At around the same time a capacitor on the Plasma Cutter went short, took some track out and stopped the unit from working, at this time the plasma cutter was well out of warranty, so I stripped it down for the repair and planned where I could  take the arc cutting voltage from:


Some circuits I drew up in a free online program:



The plasma was repaired and a resistive divider wired into the cut 40.  The board was wired up and placed into a plastic box to keep it and me safe.
Then on to testing it out and another you tube video.

I reworked a shroud to go around the drag tip to allow for my pilot arc and get air through for cooling and removing dross from the workpiece and we have anoher video.

It was now December 2016.

By mid January 2017 I had upgraded my Cheap THC by fitting a Cheap Voltage meter from Ebay (there is that word again) and a multi turn potentiometer so I had more control over the unit.

By the end of February I had updated the frame by added a shallow water tray.  ( Do water and plasma really go together ?)  But it helps to keep the dust levels down, stop thinner metal from distorting as much, but could cause a few issues.

Water does get sprayed/splashed up by the air jet and can come back at the head, try to keep the water a couple of inches below the metal being cut, I do not have this option!

May 2017 and the Cut40 has once again failed.  Flames from the PSU board, another small capacitor had failed same as last time, but this time a hole in the board.
Time to strip down and repair again, I did not take a video of the process but made something up from still images.

I got the unit working again and cut out my peacock planter.  I was asked in comments if I could provide more information on wiring up the THC, so I produced 3 videos on the subject, all very basic as all my videos are, the camaera gear is basic, but hope they help.

This gets me up to date, on this page at present, if you wish to contact me there is an email link below.


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