Plasma cutting working

We purchased a used 4x8 foot chinese router a few years ago, never used it much because we have a better local built router with super nice software. The chinese machine was cheap, local and at the time we were running our giod router all day every day and need a 2nd machine, but it was a mistake the software was too bad. So after upgrading our chinese laser cutter to a ruida controller and lightburn software, we descided the router would get more use as a plasma cutter with ruida and lightburn combo.

So we have just got it working. We are using a hypertherm max100d with cnc torch. This has HF pilot start, so torch tip just needs to 3mm above surface to start cut and works well enough to just stay at this fixed height the whole job. The hypertherm does a 1 second gas purge pre start, then starts the arc, depending on material thickness it takes a variable amount of time to pierce the material. So we are using the start delay sucessfully in lightburn for this.

Our touch is held to the machine with a magnetic brake away, so if a part falls and turns and catches the torch it will disconnect in stead of damaging something. We will add a switch to this, likely the water flow input on the guida controller, to stop the machine.

Currently not doing height control.
We are using a water table, with water 6mm below the underside of the material, as well as capturing 90% of the smoke, the water also splashes onto the underside of the material being cut, because of the air jet, and cools the material, this helps stop it from warping, so height control is not strictly needed yet, but will be needes for materials like stainless steel that warp a lot more than the mild steel we are testing with.

So it works! Cut a bunch of 2mm, 3mm and 6mm steel yesterday. The max100D is a lot more power than we need but was available for a price to good to refuse. It should be able to cut well over 1 inch thick. I think it is rated for 32mm. We are cutting 2mm steel at 100mm/second.

All the things like kerf offset, lead in and out, cut direction, sequence, we get from lightburn, happy days. Not too dissimilar to laser cutting.

We would like to Z move the head up when driving between shapes and then at first just drive back down to 3mm above material fixed height but ultimately we would like to z down until we sense the material and then drive back up from there 3mm. Plasma machines often monitor the resistance between the torch tip and the material to know when they touch, that is the torch tip can be used as the prope directly, as plasma is only used to cut conductive materials. Maybe there is a way to do this in lightburn already? I understand there is an autofocus function like this but I havent tried it and assume it is only at start of job not start of all shapes?
Some laser cutters do this also (just not conductive sensing) so maybe this kind of behaviour is already implemented?

The other features commercial cnc plasma cutters have which would be nice, are:
Height control while cutting from either continues height sensing, usualy by using an anologue value from a drag foot or brush resting on the job. Or by moniting the voltage of the arc. The plasma cut stives to run at a fixed current, say 60A, when the torch to material is a 3mm gap it takes about 100v to produce this current, if the material bows up towards the tip less voltage is need, so this can be observed, most quality plasma cutters divide this voltage down and output it within a 0 to 5v range for just this purpose. So if the value goes down the z axis head should be driven away from the material.
This hieght control is often done external to the controllers simply because most controllers are cnc router controllers and tis pid hieght control is a bit unique to plasma and high end laser, so we have already ordered a stand alone, it feeds in extra step and direction inputs into the z axis stream, while cutting is underway. It can do this standalone becuase it is just a minor changes in Z height as it goes and the main software doesnt need to know its happening.

Arc good monitoring: it is common for plasma units to output when the arc is stable, that is, if cutting is good. It needs to be ignored when piercing but should be monitored while cutting so that machine either pauses or re-pierces and resumes cutting. Arc can be exstinguished when passing over a cut line or a hole etc. Im not sure but maybe this can be used to know when piercing is successful instead of using a fixed time delay at start? Because fixed time doesn’t compensate for if a peirce is at an edge or at and existing cut, both which are much faster to pierce than a blind pierce. And piercing for too long blows out a massive hole and damages the torch consumables rapidly. The max100d has this function so I’ll connect up a light to it and workout if its timing is useful for start timing or if it should only be monitores say 3 seconds after shape start.

Just writing this up so that lightburn guys know how close their software is to being a plasma solution. It might double their market?

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The active height control would need to be handled by the controller itself. If it was supported, it would just be something we enable with a setting.

The per-cut focus touch off might be supported by some Ruida controllers, IE ones specifically made for metal cutting, but I haven’t dug into those yet - I suspect that might just be another setting, though it could also be a command that needs to be injected into the job.

‘Arc good’ testing would be similar to live height monitoring - it would need to be supported by the controller itself - LightBurn doesn’t interact with the controller while it’s running, beyond just sending the data to it.

I know we’re close - the addition of lead in/out, and start delays were done with the intention of getting closer to plasma and water jet support, so it’s good to hear it’s working. :slight_smile:


I have been meaning to experiment with using a Ruida controller to build out my CNC plasma cutter. So many of the points you have made are exactly what I have been prepared for as a fair trade off for being able to build something off of what I have now and leverage Lightburn. For me, it is really just for the fun of it.

I need to get on this.

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I formerly worked with automated welding and cutting equipment used in the nuclear power, fossil fuel and petro-chemical industry for over 13 years. The earlier equipment that was designed in the late seventies was mostly analog electronics using BCD switches to program the wire feed, travel speed, dwell times, arc length (via automatic voltage control) ect. The motors were controlled via back EMF, no encoders or steppers in site!

I mention all of this because the actual control of the equipment was hardware and not software. The Ruida controller is not made for controlling the specific needs of welding/cutting applications. You need a dedicated controller for that. That being said, you could build an external automatic voltage control/automatic gain control (AVC/AGC) and the necessary delays to interface with the Ruida.

I have been wanting to build an automated plasma cutter too for awhile but unfortunately I am running out of room in my garage for one!

Yes, HalfNormal, doing the height control outside of lightburn and ruida is possible, there are already standalone units for this, I have have one on the way. It plugs in between the ruida step and direction outputs for the Z axis and the microstepper drive. It passes through the ruida step and direction pulses when not cutting, but once good arc is detected it ignores the ruida step and direction and outputs z steps as required to raise and lower the torch to maintain the correct arc voltage. The only issue I have with this is at the start of each new shape the ruida controller will tell the z axis to stay at current hieght or drive down to a fixed start height, this will not be adaptive if the material has bowed up and hence will crash the torch into the job. So might need another hack, like interupting the z steps once the torch touches the job and better still backing off say 3mm. So this could be done as an external hack.
I’ve emailed ruida about what controllers do height control but looks like the price jumps up a LOT because the height control is only on their more expensive controllers

I happened to find this open source controller. You would be able to program a retraction between parts.

Great find.
Possibly the air assist output could be used to trigger the z auto hight find function. I’m unsure if it currently just outputs the whole time the job is running? For some applications were air assist also keeps smoke off the laser mirrors and lens, this is the function you want, on higher power lasers the assist air can be expensive bottled gas, so you want it on only when cutting and not wasted when traversing between shapes. But becuse you might want pre and post flow, it needs to be a seperate output to the laser on output.

So if ruida and lightburn support this cut shape only air assist mode, a seperate output that can be triggered say 3 seconds each time before the laser fire signal is triggered, then that would give an independent controller, enough time, to use the ohmic tip sensor, to find the surface of the material, back off say 3mm above the surface. When the 3 seconds is up, the laser output triggers the plasma to fire, then the curent start delay in lightburn could be used to allow the pierce to be complete before moving off.

Would be best to wait for feedback for when the pierce is good. But a cheap laser controller like rdc6445g doesnt have this function, so a fixed timer will do.

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