DIY ShopBot CNC Plasma Project

[DJDLabs]

This will be my first post here. .. Also my first CNC project!



If you have a moment I will walk you through this interesting project.
It all started with an Auction had for almost nothing a broken First gen Shopbot.

The unit had been sitting for almost 9 years in an old warehouse. All of the wires had been cut to it the controller and PC where missing.
Here it is loaded up.





It had a suction table on it when I got it, but sadly was damaged, and the PVC was so brittle just touching it would have it crack.
So I removed the table, knowing it would be destine to be a plasma table!
After a good bit of manual labor help from a few friends, it is now in its new home.




So now the work begins on trying to get this thing working again!
First step was to get the frame cleaned of 9 years of dust and funk, thank set out to get everything level and square.
This is when I discovered, at some point the table must have been hit by a forklift or other large object, the frame was 2″ out of square! The gantry was jammed solid and would not even move.




So I continued to go through and level and square everything. This was a good 2 day job.
But it paid off, I was able to get the gantry to move again!




Next step was a full rewire to go through and check all connections, and replace damaged wires.




Made a point to run every wire inside the Uni-Strut to keep it safe.






It has these cool bows that are used for cable management, I kind of like them over the normal tracks.




Next, on to building the controller!

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[DJDLabs]

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

I than worked on mounting the TinyG ( I do wish 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 noticed 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!

[DJDLabs]

It worked!







But….. I would only get about a few seconds of cutting and it would stop.

After some troubleshooting I found the TinyG would lock up solid, i would get no response, could not terminal in, nothing.

I have to hard power cycle it to get it back.

So spent a few nights trying to figure out what was going on.

I narrowed it down to the Pilot arc start on the plasma, the second i would press the button to fire it, the serial connection would dump out to the TinyG.

Hmm.. what to do?

So I started shielding.. everything!












Sadly, this still did not do the trick.
so I went and got some Ferrite cores and shielded everything I could to the controller.

Still, same problem, so I check and remade all ground connections, even made my own grounding network, still no luck.

In the process of scoping out the problem, I was not able to reach the USB connection well, so I grabbed a new longer USB cable.

The problem went away.. and never came back.

It was the USB cable!! All this time. The longer USB cable, had better shielding, and was able to prevent the FTDI chip from freaking out on the pulse spike.

Whew, I can now get back to working on building, and not troubleshooting!

Here is the quick torch mount I made up.



Soon, to have a slide, that will allow for better torch height control.

Next, calibration..

[DJDLabs]

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 straight 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!

[DJDLabs]

Here are some logos, the first one was a test run, sadly I did not have the setting correct, but do like how it came out!



Next test,



I had to get the grinder out and throw a quick edge onto the ‘Baterang’



So after all of that fun, I was still running the plasma by hand with a push button, I needed to interface it with the TinyG, up next is how that went.

[DJDLabs]

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.

[DJDLabs]

Forgot to mention the computer ‘kiosk’

This allows me to swing it around, up or down, depending on the size of the work I am working on. That and if I want to stand or sit.







Now that it was working better, it was time to make a better Torch holder.

So I took apart an old Dell monitor stand, and used this as my torch holder.






This allows for a rigid mount, that can break away. ( zipties. ) if needed, also it has give in the 'Z' so I can put a switch to measure material thickness.

So now it was time to test the accuracy of the new mount and system.










Next up was to test some thicker stock, here is some 3/16"







Seemed to work pretty well.

Next project is to build a full water tray and slats for it, so I can start cutting full sheets.

Also plan to dig around the forum here to find some feed rate/ amp setting to use, for I have been guessing most of the way here haha.


Thanks for your time thus far! If you see any way to improve the project let me know! Always open to suggestions.

- - - Updated - - -

In the event anyone asks what the random Whitewall tire is from,

It is my custom built 1963' Jacobson Tractor.

[DJDLabs]

Here was a full table 'test' cut to see how accurate it was over the entire table range.

[mrniceguy]

I realise this is an old post but cool build!

How do you generate your G code? Does your torch do the touch thing before each cut? THC?

[C0matoes]

I am currently setting up a shop bot plasma table. I'm pretty new to this but I believe the "touch off" action is only really nessesary if your torch power supply does not use a pilot arc. Of course I may learn something different when my THC arrives in a few days but as of now I don't really see a need for touch off unless I'm using it to zero the top of the plate. I'm still learning the g code so currently I'm using the standard shop bot coding which is pretty straight forward and easy to learn. I would appreciate and tips or tricks you may have learned about keeping interference from the plasma to a minimum as it seems the usb connections are finicky.

[asuratman]

I plan to purchase plasma cutter that do not have pilot arc, it is recommended or not for cnc application? If do not have pilot arc, then touch off action is needed. Which one is better, to have pilot arc or not. Let me know.

[C0matoes]

A pilot arc is always a good option as it doesn't require contact to ignite. The touch off, as I learned yesterday may not be nessesary but as I'm testing I believe it is desired as it will make it easier to determine when to ignite the arc in your code. Touch off, ignite, run cut, torch off, jog to next cut, touch off, ignite, etc. etc.. I'm currently at a stopping point waiting on some control relays , THC, and the power company to drop in my 3 phase power. My torch (an A120) will burn single phase but the thing pulls 95 amps. Shop bots come with a prescripted touch off routine built in but support and information regarding setup is scarce to say the least. One tip Ive realized is, don't run the touch off routine without the equipment to do so in place as the z axis loses its mind.

[Torchhead]

Touch off is not to fire the torch. Its a measuring process . It turns the torch tip into a surface probe. .Its known as IHS (Initial Height Sensing). All cutting is done form the Top-of-Material.. no matter how thick it is or how un level or warped, you do the pierce height and the initial cut height (Before yon turn on a THC) based on where the top of the material is at that spot. Its better to have a touch-off and no THC than have a THC with no touch off. Shopbot was designed to be a router and plasma was added as an after thought. Depending on the controller and the control software setting up a THC may prove to be a challenge. Unless they gave up and later supported MACH there will be problems with making a THC work. I have not kept up with ShopBot in several years so everything I say may be wrong.

[bigforkg]

What type of controller are you using? I want to build a cnc plasma, but I would like to use open source. I have a Arc pilot plasma already but Im stuck on the, delay for pierce.

[C0matoes]

I'm using the ShopBot controller which uses Gecko drive controllers. Initially we had some trouble getting the USB connection not to drop the connection when the torch pierced the sheet. Because we needed to get some material cut we came up with a temp solution of isolating the cut table from the cnc table and it works pretty good until we can rebuild the table wider. I can say, ShopBot is about as helpful as tits on a boar when it comes to their machines. They don't seem to be very knowledgeable at all. Our temp solution for firing the torch manually consists of a roller switch and guide plate to fire the torch and a pushbutton switch to prevent crashing. I know its a bit archaic but it works for now. I've not hooked up my THC yet but will once I get a better anti-collision setup in place. As far as pierce delay I would assume that it will be slightly different depending on the torch itself. What I did was rewrite the ShopBot plasma files to work with my switches and no THC. MY pierce delay is set a .2 seconds and seems to work fine at that. My consumables seem to be lasting pretty good with plenty of cut time at that rate. The A120 we use is a pretty hefty torch so your delay may need to be a little longer but the only way to figure out what it needs is to try it out, just make sure its impossible for your torch to crash before testing. I highly recommend isolating the cut table from the cnc table. It will save you a lot of time trying to fight shielding and interference issues, at least it did for us, others may have different solutions but I like to keep it simple. Torchhead is correct about the touch off and THC. The THC should be setup after IHS is a stable process or you'll be buying another torch head when it crashes into the material.

[marcov]

Do you mean breakout board? I think is a tinyg from shyntetos!

What type of controller are you using? I want to build a cnc plasma, but I would like to use open source. I have a Arc pilot plasma already but Im stuck on the, delay for pierce.

[C0matoes]

Pierce delay for my torch on most materials is .3 seconds. The pierce delay to me isn't as critical as the speed of the pierce. Depending on the material thickness the dive of the torch may need to slow down but the pierce delay would stay the same. Keep pierce delay as short as possible as the torch is riding air at this point and the longer the delay the more rough it will be on consumables. Most if not all open source software will work for plasma since it really has no idea or concern over what tool is attached to the CNC system. I have two types of systems running, both open source, and each has its own learning curve. One runs Ubuntu w/ LinuxCNC, one runs windowsXP w/ShopBot software. ShopBot has its own firmware for use with its controller cards. I would say that a Linux based system is faster at processing and better at precision than the windows based systems but the Linux will take a bit to get used to if you've never used Linux. After toasting my control card I would highly recommend, if using a USB style control card, that you purchase an externally powered USB hub with overload protection just in case you get a spike.

[coherent]

we came up with a temp solution of isolating the cut table from the cnc table and it works pretty good.

What exactly did you isolate from what and how? I have a g540 and a cheap lotos pilot arc plasma cutter and would like to set it up a plasma cutter on an old cnc router. I've heard others mention the controller dropping the signal to the machine when the arc fires, so interested in your temporary fix.

[C0matoes]

1/2" 2300V GLASTIC ELECTRICAL STANDOFF INSULATOR ISOLATOR 2015-4C | eBay

I'm using these ^, we are resting the water pan/cut surface on top of these so we can just remove the entire cut surface if we need to dump the pan. Perhaps there is something better but I just happened to already have some in my junk piles but they are pretty cheap. Originally we just used some scrap plastic we had laying around but it proved to not be resilient enough to the heat. After dismantling our machine to increase its size and add a water table we also noticed the table leg had grounded out through the concrete below it to a piece of rebar close to the top of the slab so we're also adding some isolation to the adjustable feet. Since larger feet are so pricey we're just using some 1/4" orange rubber mat like the power guys use when working on the power lines. We got energy through the USB port as well. 90% of USB ports aren't surge protected or fused so a protected/powered hub needs to be between control box and control PC. No need cooking them both from a surge. We have gecko drives which offer protection so it only cooked our power supply which ended up being pretty cheap to fix.