Black Friday Deal got me :)

"The 300V version of the THCAD has all input divider resistor on board and can connect directly to the plasma voltage of touch start type torches only."

this was the section of the description on the Mesa site that confused me.

my understanding so far was the THCAD-2 can be used but you have to add the HV resistor for ir to work and the THCAD-300 does not need the external resistor in my application;

I would stick to the thcad-2 with a scaling resistor. I can't really see a use case for the thcad-300
Please use a seperate 48v 7-10 amp power supply for motors.  24 v is waaay underpowered
Meanwell MDM-60-24 and  MDM-10-5 would be better choices than the cage power supplies shown.
All motors should have a seperate ground wire back to the star ground so emi does not attempt to pass across linear bearings. Hyrperthem have a good grounding document. Follow it.
I get frustrated when I see suboptimal designs accepted as gospel just because they have used pretty pictures but its a good start
Grab a couple of Mesa COMMX2 bus bars when you get your 7i96s. Also get some of their Din rail mounts.

Also just for me, use a multimeter and check if there is resistance between the torch tip and the work clamp. Most plasmas add a 100k resistor or similar to bring the current on the raw output down to non lethal levels. If so, you can mount the thcad in the control box if you are lazy.

Sorry, should have set check resistance from the cnc output to work clamp

the cheap drives i got are only rated for 42V so i am looking to run them on 36v, this is going to be on the cheap side for builds. i don't do things as pictured by others i just use it for a starting point for planning. i plan on using double shielded wires everywhere with shield drains on everything. i have spent a lot of time reading up on grounding and a lot of it was plasma related for a source. i have seen way too many builds get sideways because of grounding issues

the Nema 23 motors i picked up and dives were only $110 for 4 so nothing very fancy. THCAD is about the cheapest height control on the market, so being able to do that makes me happy

i'm not ready to buy boards from Mesa just yet and the THCAD-300 is out of stock at the moment, and it is a little bit cheaper than the THCAD-2 so with added cost of having to buy extra stuff with shipping on top of that saving $20-$30 makes me lean towards the THCAD-300 just because i am cheap

nah, go 48v if your drives can support it. its the current which matters. You could drive the motors at 72 volt with the right drivers if you wanted and still not break them,

   

this is what i went with and the cheapest is what drove this decision. Since i have never done a plasma machine before top-of-the-line stuff is is not something i want to do on a first-time build for plasma., these drives are rated for 42V so 36v is safe and should do what i need them to do. i plan on keeping the gantry very light, plasma should not need anything to rigid. my thought is 11-gauge square tube should do fine, i honestly don't think you need much more than 1 linear rail on the gantry maybe 2 on the Z but 1 there too would probably be enough.

i will be doing my planning in fusion 360 to work out a final game plan, i might try to design things so i can add a rotary later down the road if i want to get into than later. This straight torch is pretty long so a z with lots of travel is probably something i will factor into a design. Z height is something i would avoid in a milling application but with plasma it should not matter much.