Another DIY CNC Plasma Table (Small story)

[AdrianH]

Go back a few years and I bought a cheep Chinese style plasma cutter, the same as you see on Ebay and Youtube, mine was a cut40. It did and still does well for me for cost which was £180 (UKP). At the time I was happy just to get a faster and quieter way to cut metal rather than the angle grinder.

I made a pantograph with holder for the torch as a way of cutting out shapes, but the geometry was off a bit so they never turned out correctly, so I started on a small frame around 100 cm by 70 cm, built the table still using the same cut40 plasma unit. This meant the Z axis was floating in that once I moved to the start of the cut position the torch would then drop onto the metal and the weight would keep it there and I dragged the torch across the work, it was a drag tip after all.
I did change it to a straight torch rather than the normal handle at around £35 (UKP) it was not breaking the bank.

This worked good enough to make things for colleges such as a motorbike sign, cut the odd cat and bird shape etc. The software I was using at the time was an old Dos package called CNCPro by D Yaeger. Failure of my old Dos machine meant I had to look for something new, so armed with another old Windows XP machine I turned to Mach3 which had a lot more machine options available if only I could use them.

So I had a rethink and by hand tried to see what torch height I could get when cutting, up to around 6mm the torch started to sputter and then the machine went bang. Stripping it down I found a small capacitor had failed, but it did give me chance as well as the repair to have a look at the boards and figure a way to get the cutting volts out of the machine. So a few components later and the cut40 is back together working again, non the worse for wear.

A bit of reading of forums and coming across this forum and posts by Jim and papers from Hypertherm etc, I knew that I would need some form of THC, but and here is my big but, being not for commercial use I felt as though I could not justify spending a few hundred pounds when the total setup only cost hundreds rather then thousands of pounds. So back to basics arc volts go higher the more off the work you are, need to set a voltage as such as per the manual for the cut 40 which is 96 Volts, sounds like a voltage comparator. But I would need 4 of them, one to tell me to go down, one for up and two to see if the arc volts were in a set range to determine if the arc was OK.

So a search of Ebay found a 4 comparator board for a grand cost of £10 (UKP), I ordered two.

When the boards arrived I boxed things up in a small plastic box with a external DC isolated power supply, a few components added to the cut40 to give a 10:1 voltage divider and spike suppressor, a capacitor on the now THC controller to slow things down a little bit, set up the posts to gave an arc OK signal if the volts are in the range of 75 to 130 Volts and the final two pots to give me up and down around 96 volts, with a small dead zone in there of approx 2 volts.

Next back on the table and I added a micro-switch to the floating Z axis so that I could probe the top of the metal, write a new post for my set-up calibrate the probe function and have a go. To say I was surprised it works is an understatement, it virtually gets rid of bevelled edges when I set it up correctly a lot of help was gleaned and gained from the mach3 forum in the setting up.

The total cost of parts which has happened over the previous 18 months as I played with the project is probably in the region of £700 (UKP) and that includes controller, motors and cut40 etc. It will never be as good as a commercial unit and the wonderful Hypertherms and other top end machines and it is not trying to be as good as them, just the best I can make my hobby machine to fit on my bench in the garage.

I saw the post on this forum a week or so ago about the Split Monograms so decided to have a go, and here are two I have done for Family for Christmas.

coat3.jpg

coat2.jpg

Cheers

Adrian

[acourtjester]

Very nice results for your DIY project, Time and energy well spent. If you let the work get out you may be earning some money with your hobby.

[AdrianH]

I am not sure if this will work, but just in case anyone wants to see the basic cheep THC in work then have a look at this Youtube.

https://www.youtube.com/watch?v=uongcUZbv6Y

It probably works with my set-up as it is slow travel speeds.

Adrian