CNC Plasma cutter - Z-axis

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GideonRT
Posts: 1
Joined: Sat Dec 02, 2017 2:41 pm

CNC Plasma cutter - Z-axis

Post by GideonRT » Sun Dec 03, 2017 3:42 pm

Hello everybody,

first of all, great website with a lot of information! =) It is the only reason I started my latest project.

a few months ago I upgraded my Prusa Mendel 3D printer to a Wanhao Duplicator and have been looking for a new use for the Prusa parts. So when I found this website I decided to try and make a CNC plasma cutter. I already had the plasma cutter and I adapted the torch to fit into the CNC machine 'head', which is able to move in the Z-dimension. I kept it relatively small with the max cutting range around 50x50 centimeters. To control the cutter I have an Arduino Uno and CNC shield V3. I thought I bought an original CNC shield, but I fear it's a Chinese copy.

The CNC machine itself and wiring is done and, after reading about a lot of projects, i'm relatively sure i'll be able to make the X and Y movements work. I'm not sure however, how to make the Z-axis movement and ignition sequence of the plasma cutter work.

After placing a sheet of steel in the machine, my idea is to manually move the torch/Z axis so that the tip of the torch contacts the steel. After starting the machine, it needs to move the Z-axis up around 1 mm. This way the head can move freely without damaging the tip. i'm thinking this command goes in a startup block.

When actually making a cut, the Z-axis needs to come down again (1 mm, again touching the sheet), send a pulse to a relay to start the cutter itself, and go back up 1mm again before starting X/Y movements. I'm hoping to get some advice on this part.

- Can I use GRBL's PWM functionality to activate the relay, say command M3 or even a coolant pin (M7 or M8)?
- The ignition sequence is the same every time, is there a way to include it in the firmware somehow, or is this a sequence of movements that needs to be included in every gcode file (for each separate cut) i want to send to the machine?
- Regarding my previous question, i'm thinking it needs to be added for each cut in each gcode file. After all, it is a tool path. Is there an easy way to do this?

I'm thinking about using Inkscape to generate the gcode I need for cutting and I know it has a lot of plugins. The 'Makerbot Unicorn G-code output' actually comes pretty close to what I need.

Any ideas and suggestions are very welcome.

Bertus Kruger
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Re: CNC Plasma cutter - Z-axis

Post by Bertus Kruger » Mon Dec 11, 2017 6:53 pm

GideonRT wrote:
Sun Dec 03, 2017 3:42 pm
- Can I use GRBL's PWM functionality to activate the relay, say command M3 or even a coolant pin (M7 or M8)?
Yes... firstly set the spindel speed to 100% command is -> S1000

Then use the M commands to enable and disable the pin. The pin can then be connected to a relay board to switch larger currents.

Bertus Kruger
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Posts: 1457
Joined: Wed Feb 03, 2016 10:26 pm
Location: Wellington , New Zealand
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Re: CNC Plasma cutter - Z-axis

Post by Bertus Kruger » Mon Dec 11, 2017 7:00 pm

GideonRT wrote:
Sun Dec 03, 2017 3:42 pm
- The ignition sequence is the same every time, is there a way to include it in the firmware somehow, or is this a sequence of movements that needs to be included in every gcode file (for each separate cut) i want to send to the machine?
- Regarding my previous question, i'm thinking it needs to be added for each cut in each gcode file. After all, it is a tool path. Is there an easy way to do this?
GRBL can do startup commands but that only runs once per startup. I would think the startup process will need to be included for each separate cut.

This can be done with scripting but you will need to identify each time the Z move up and insert a startup sequance when it goes down again. Should not be to hard to do...

What would be nice is if you had a automatic torch height controller that does this automatically for you.

dano
Posts: 1
Joined: Wed Jul 03, 2019 2:26 pm

Re: CNC Plasma cutter - Z-axis

Post by dano » Wed Jul 03, 2019 2:37 pm

Hi Gideon,

I would like to know what did you finally do.
Did you solve the way to control Z axis height and the plasma output, or did you keep it manual?
What steel thickness are you cutting?

I would appreciate your feedback as I have the same project. I was thinking to keep Z axis manual and control the plasma trigger with a relay. But maybe it would be better good to control the Z axis with the arduino, but I have the same doubts you have.

Greetings

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