TinyG – Shopbot – Plasma project.

I started with an old Rack case i had from another project.

I than worked on mounting the TinyG ( I do with it came with its own standoffs! )

As well as the power supply and a Volt/Current gauge onto the case.

At first it looked like I had a ton of room, but that starts to fill up quickly.

Here I got the motor wires in to start testing.

This is where to fun began.. Setting up the TinyG to work with the old Shopbot motors. I was able to find an old data sheet that helped get things setup but nothing listed the distance per rev.

I came to find out the motors have a build in gear reduction of 6:1

So first thing first I strapped a router to the unit and did some test cuts.

Egad! That’s not good. I am getting drift and mist steps that and the noise oh the noise!

So after allot of troubleshooting I got this,

So what did I figure out?
Well I may have missed it in the wiki, but every time I made a system variable change, I notticed nothing would change in operation, if I changed step rate or in/rev nothing would change, so i would get frustrated shut it down and start again another day, only to find it not working or in bad shape, so I would make some changes, nothing would happen and the cycle would repeat.. I was about ready to pitch the TinyG thinking how unreliable it is… then it hit me!

After you make changes, it will reflect them, but you have to reset the TinyG for it to implement them! BAH! So once I figured that out, I was finally able to work at fine tuning the system.

In the process of all of this my plasma torch came in!

It is an 80Amp CNC torch I scored of ebay cheap! And came with a 13′ hose!

I ordered one with Pilot arc, so it can strike the torch without contact with the metal.

So I set out to build my own Plasma cutter power supply. I was stepping down 240V to 120V at about 60 amps. I than ran it through a massive Bridge rectifier, and large cap bank to give me just shy of 180VDC.

I used a 19Kv DC power supply for my pilot arc. and (2) massive 2Kw isolation transformers in parallel to keep me safe. last a set of stacked variacs for voltage control.

I got everything setup, and it worked!!!
… for about 20 seconds, the very next time I struck and arc, the insulation in my isolation transformer broke down, sending the 19Kv back through my panel, the massive current spike from the caps, blew my main breaker in the panel, but because of the high voltage DC, only one leg opened, the other was left floating at 8 Volts! Eeek… This was not good. Fortuitously I have a 100Amp DC contractor that was able to break the loop upon the drop out of the 220.

This lead me to the idea It is not always best to build you own, so I went and bought one.

So I picked up this guy Lotos 60Amp Pilot arc plasma cutter power supply.

Next lets see how it works with the system!

Like I said above, getting the travel rate correct was not easy, mostly measure to get close then fine tune with real cuts.

After a few hours I was able to get circles spot on!

Next step was to try out building a GM disk brake spacer.

Worked, but ran into some problem, Chilipepr would not do inside contours, it simply ignored the circles and made all arcs streight lines.. so I had to break the part into 2 drawings inside Sheetcam to make it happy.

I will have to work on isolating down this bug.

But for now, lets cut some fun stuff!

I first connected up the spindle output to a solid state relay rated down to 3V. I figured with the 3.3V output this would be fine.. Nope.

If I measure the output it is only 2.99V not enough to fire the solid state. Bummer.

Looking at the schematic, it looks like the on board LED and resistor are zapping some of the current. thus bringing down the voltage.

So this was my ‘solution’

‘

Used a 2N3904 NPN transistor and a 82K Resistor. I had the relay connected to the 3.3V rail on the TinyG and the ground through the relay back to the Collector.

This did the trick!

So next I ran the solid state to a 120V 2 pole double throw relay. This is what will run my Plasma torch.

Here it is wired up the switch and red button in the middle are for torch control.

When you feed hold the tinyG the spindle remains energized, with the plasma this can be bad, so I have the switch to kill the control to the plasma. The red light lets me know when the TinyG is calling for plasma, so I do not turn it on if it is stuck on sort of thing.

the red button allows me to manually fire the plasma as needed.

Next step was to clean things up.

Here is the power supply and plasma in place. The ‘E-Stop’ kills power to the controller to stop all motion and plasma.

Also tried out a Spiderman logo test cut.

Here is a quick video of the cut.

I feel kind of bad showing off my messing wiring, so here are some shots of the Shopbot I wired up at work.

and than mine at home,

Oh well, I keep telling myself, this is ‘temporary’ until I get time to build a shed for it to live. 🙂

Here is a link to many more pictures of the project.
https://www.dropbox.com/sh/2mo0je0prj17bsf/AACtm6gI8wsHCx6wLhpTxZOda?dl=0

Next on the project list is to build a full water tray and support rails for the work.

So stay tuned, more to come!