looking to build a custom THC - need more info.

[jouellet]

Hi folks,

First, a little bit about my CNC/Plasma experience. I have already built 2 CNC, which are using the cheap chinese parallel port. I'm also using Mach3 as the operating software. So far they are both running fine .

I recently bought a used plasma, a Miller Spectrum 2050, which came with a hand torch and a machine torch. My intention is to build a CNC plasma table. I'm planning on using another one of those breakout board. Mechanically speaking, I'm very confident it will work.

The "grey zone" that I'm dealing with, is the THC . Feel free to correct my assumptions or statements.

My understanding is that this device will receive a "start" command from Mach3. The THC will then position the torch to the requested height, then send a "OK" signal to Mach3. Upon receiving the "OK" signal, Mach3 will the fire the torch, wait a bit of time then start moving. Once the cut segment is done, the trigger signal is removed. The CNC will then start moving to the new cutting position (X & Y)

Am I right so far ???

I want to build my own THC. I have a bit of experience in electronic design so I should (no braggin' here) be able to come up with something. Here are the basis of my design:

• The THC would be the one controlling the Z axis.
• Device would have a LCD display, where target height could be set.
• I'm thinking of a height adjustment between 2 to 8mm.
• A 5 VDC signal (from Mach3) would initiate the positioning sequence.
• A dry contact would close when torch height in within range.
• When no trigger signal is received, the height would go to 15mm (safe position).
• Height would (slightly) be adjusted while cutting.
• My "custom THC" would not interfere directly with the triggering of the Plasma. Mach3 would take care of that thru the switch on the machine torch.

Any thoughts of my "project" ?

Anything that I did not understand properly ?

Any suggestion ?

Now, if I have "passed" the test of "examination by my peers", anyone has an idea where I would need to connect it on the breakout board ? I have included a picture of the board that I using.

TIA

Jasmin




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[tjb1]

Hi folks,

First, a little bit about my CNC/Plasma experience. I have already built 2 CNC, which are using the cheap chinese parallel port. I'm also using Mach3 as the operating software. So far they are both running fine .

I recently bought a used plasma, a Miller Spectrum 2050, which came with a hand torch and a machine torch. My intention is to build a CNC plasma table. I'm planning on using another one of those breakout board. Mechanically speaking, I'm very confident it will work.

The "grey zone" that I'm dealing with, is the THC . Feel free to correct my assumptions or statements.

My understanding is that this device will receive a "start" command from Mach3. The THC will then position the torch to the requested height, then send a "OK" signal to Mach3. Upon receiving the "OK" signal, Mach3 will the fire the torch, wait a bit of time then start moving. Once the cut segment is done, the trigger signal is removed. The CNC will then start moving to the new cutting position (X & Y)

Am I right so far ???

I want to build my own THC. I have a bit of experience in electronic design so I should (no braggin' here) be able to come up with something. Here are the basis of my design:

• The THC would be the one controlling the Z axis.
• Device would have a LCD display, where target height could be set.
• I'm thinking of a height adjustment between 2 to 8mm.
• A 5 VDC signal (from Mach3) would initiate the positioning sequence.
• A dry contact would close when torch height in within range.
• When no trigger signal is received, the height would go to 15mm (safe position).
• Height would (slightly) be adjusted while cutting.
• My "custom THC" would not interfere directly with the triggering of the Plasma. Mach3 would take care of that thru the switch on the machine torch.

Any thoughts of my "project" ?

Anything that I did not understand properly ?

Any suggestion ?

Now, if I have "passed" the test of "examination by my peers", anyone has an idea where I would need to connect it on the breakout board ? I have included a picture of the board that I using.

TIA

Jasmin

I would have the control send the arc start (M3) command to your THC, have your THC locate the workpiece, set the pierce height, and fire the torch and when your THC receives the arc ok from the plasma cutter (if you have that signal available) I would pass that on to the control which will start movement. This would make it much easier to interface with any of the control software like Mach3/Mach4/UCCNC as they all are setup to wait for the arc ok signal before moving. You will need to set a dwell (varies depending on part thickness) after pierce before moving to cut height, on a Powermax 45 most of the piercing is done at .15" and the cutting is around .06". I'm not sure how you would handle end of cut as you need the M5 signal from the control to turn off the arc but it's going to send that and move so you would either need a dwell long enough to assume the THC has moved to 15mm or wait for an input before moving.

I don't see any mention of voltage monitoring in your post. THC is done by monitoring arc voltage and maintaining that by adjusting the height, this target voltage varies on the cutting amperage, consumables, and material thickness you are cutting. You will also need a stepper motor controller and a limit/home switch to know where the 15mm is. Maybe on power up, it will always move up to the home switch?

I've made my own THC using a Teensy, Mesa THCAD and an LCD. It check the arc voltage around 180k times per second (based on loop time with a Teensy 3.1) and sends up/down signals to the control and can be built for around $100, you can find more information here if you're interested in how it works or building your own - https://www.cnczone.com/forums/gener...t-control.html

[jouellet]

Hi tjb1,

The machine torch that I have seem to have only a trigger switch. I have searched a bit and did not find that it has any other form of control. This being said, monitoring the arc does not seem a viable option, unless I open up the unit and try to "tap" myself to some sort of signal for the arc. This leaves me with only height as a method of control.

For my initial height sensing, I was planning on using a mechanical device to position it. Something like this:

https://www.aliexpress.com/wholesale...+Type+25-100mm

Now, while moving, this is not a viable choice, so I was planning that after initial position is found, I would be using an IR sensor, but I'm not sure that with all the sparks, it will provide accurate reading. The sensor I've ordered to do some test, is the following:

https://www.ebay.com/itm/2PCS-Sharp-...72.m2749.l2649

I'm at work right now, but I will definitely have a look at the THC you've built, and if I may, I'd like to get in touch directly for some advise.

[tjb1]

Does the scale have a way to retract it? It can't hang lower than the nozzle tip while you're cutting. Many people use floating heads with a sensor to detect when it moves, you can see this on mine here:

You use a probing sequence like G31 that stops when the input triggers then you send something like G92 Z-.6 (the .6 being the distance traveled from hanging until it trips the sensor) and then when you go to Z0, the torch should be hanging and barely touching the metal. I have no input on the IR sensor but I know from reading about them being used in 3D printing, they seem to have issues with different colors/surface finishes.

Is there a reason you decided to control Z axis directly instead of sending inputs to the control?