My cheap CNC plasma based on a cut40, with THC

[AdrianH]

This has been an ongoing project for me for some time now, and I can appreciate that building anything CNC is not new to the forum, there are some very good home made units out there.

My CNC plasma unit is a very small bench top system, and it literally sits on a small bench in my garage, it is a constantly evolving system as I learn more, use software better etc. But apart from having to buy software, I had a major thing in mind, I could not put much money in to it, so the thought process for me was what could I add/change that was cost effective in all but time.

Now I started as mentioned in the title with a cut 40, so 40 Amps max at 60% duty cycle, drag tip design, and no pilot arc. Over the months I have added resistors to allow the cutter to provide a basic pilot arc system, with a few mods to a home made shroud to facilitate this, a switch to allow for zero height adjustment, to a very cheap idea for Torch Height Control driving purchased software, Mach3. Finally to sticking a water tray under the unit to greatly reduce the crud that it throws around the place under pressure.

The pilot arc, zero height adjustment and THC means I no longer have to drag the tip across the work-piece, so it means I get get faster speeds when cutting as the table does not have the friction to compete against, it means warpage can also be taken into account (within limits).

So I thought for those interested I would put the idea forward regarding a cheap THC, by cheap, I mean cheap, a few tens of pounds. It means you do need to have some electrical/electronic knowledge and skills with a soldering iron, and a Cut40/50 that is out of warranty.

It is all based on a 4 channel voltage comparator board sold on Ebay, a 12 Volt fully isolated power supply, i.e. regulated transformer based plug top around 1 Amp. A handful of resistors and capacitors. And with this you can provide outputs such as ARC OK, move up and move down signals to drive Mach3

A voltage comparator basically allows you to compare one voltage against another, generally a variable voltage against fixed voltages to switch on and off relays etc.
The board is available off Ebay for less than £10 plus p&p. You also need to add a resistive divider to your plasma cutter and this is where the out of warranty part comes in as it meant taking mine apart.

On these cutters they are designed around a 96 to 100 Volts across the cutting arc, added with lots of volts to start the arc (HF start), So I added to the plasma cutter a 10:1 resistive divider to reduce the 100 Volts to around 10 Volts and added a bit of filtering to the divider to reduce the effects of the HF start together with careful picking of the input points in the plasma.

So I sample a reduced arc voltage and apply in in parallel to 4 voltage comparators, two together provide ARC OK signal, one provides a move up and the last move down signals via relay outputs to Mach3. It was initially done to maintain a fixed arc voltage of 96 Volts (for my cutter) and it did this by moving the head up or down with Mach3 driving my Z axis stepper as required. Later addition of again a couple of cheap things off Ebay such as a 3 wire volt meter and a 10 turn variable resistor meant I could adjust the height to suit a variation in arc voltage, there are videos on how I wired up the unit explanations of how the idea works etc on youtube for those of you that are interested in this type of thing.

BUT and this is a BIG BUT. If you have paid lots of money on your Hypertherms, Miller or other style of high end plasma cutters do not do this, stick to the units recommended for your machines, if however you are like me, more time than money, only do this for a hobby and more importantly like to play, then have a view of the video's, assess the risk to you and your gear and have a think. It's all do at your own risk.

Thanks for getting to the end of this post, without falling asleep, have fun but stay safe.

Adrian

[Frank S]

great little machine With a bit of fine tuning IE lowering the heat looks as though it will do the same job as a machine costing 20 times as much

[Frank S]

Not sure I could do this to my Miller Spectrum 701 though

[AdrianH]

Most of my cutting is done in the 20 to 30 amps range as I figure that would be within it's 100% duty cycle, if I had circuit diagrams I would probably try to make it adjust down to 15 Amps cutting, but no not something you would do with your Miller, as it is not really a machine I would describe as being at the cheap end of the market

Adrian

[DIYer]

Thanks AdrianH! We've added your CNC Plasma Cutter to our CNC category,
as well as to your builder page: AdrianH's Homemade Tools. Your receipt:

CNC Plasma Cutter by AdrianH

tags: CNC, plasma

[Frank S]

No not on the cheap end for sure .but the machine would be a lot more useful if I would take the initiative to construct a CNC machine to use it with.
As it is now I would rather grab my act torch than bother with the plasma

[LyleD]

Hi AdrianH,
Thank you so much for the post and for making the plans available. I've got to build one.