Steppers - I'm using the StepperOnline NEMA34's to retrofit my mill. I've not run them yet, but, they appear to be rather good quality. I'm not impressed with the cable connections - those will be replaced - but otherwise I'm satisfied. More importantly, they have alarm outputs (for the E-stop circuit), and you can change the encoder count deviation alarm in the drives using their free software. Both of these features were mandatory (for me).
It really depends on what's easily available to you, but I'd shy away from the no-name Ebay stuff. The StepperOnline offerings are probably about the same as most Chinese ebay things, but at least they've paid to have different color drives and they have an actual web site with actual tech support. Small but meanful reasurrance (for me, anyway).
StepperOnline also offer a higher-specification series of steppers/drives that I suspect are genuine Leadshines (rebranded) if you want to spend more money. Those are creeping up on cheap servo prices and their Y-series (from your post) appear hit the sweet spot for performance vs. cost.
Belts - For the stationary belts I'd suggest AT5-30mm. It really depends on local (to you) availability, but the AT belt profile is better than common HTD for backlash. Real Gates GT2/3 belts 30mm wide are very expensive but are also good for positioning applications. If all you can get are HTD belts, fine. You can always have the drive pulleys hard-anodized for a few dollars to decrease the tooth to belt gap and reduce backlash.
3mm pitch belts are going to be very hard to find in 30mm wide, and 8mm pitch are too coarse. The drive pulley will be very large, which will require a greater than 5:1 primary reduction ratio - not practical with a compact belt drive. So the 5mm pitch hits the sweet spot using a 16T drive pulley and a 3:1 or 3.5:1 primary reduction. The 5mm-16T pulley is the smallest pitch diameter recommended by a few belt manufacturers for decent belt life. And use the largest possible idler pulleys to reduce back-bending stress - think 35-40mm.
For the primary drive HTD5M or AT5M, 20mm are plenty stiff. Get whatever your bank account can support - the AT pulleys are a bit pricy.
Gantry - depending on your desired cutting area (1.7m, right?), I'd get a 2m long, 75mm square aluminum tube, maybe 4-5mm wall thickness and use that as my primary gantry tube. The rails will be hot-rolled steel strips, 100mm wide x 3mm thick.
Don't get a big plate and have them cut out - you want the rolled/rounded edges that strip steel generally has. Drill & tap 6mm holes every 100mm near the top and bottom of the tube sides and bolt the steel strips on. The strips should have generously oversized holes to permit alignment/adjustment. This combination will be lighter and stiffer than using extrusions, and probably cheaper too. Just a bit more work drilling the holes.
Software - you can't go wrong with LinuxCNC, and the new(ish) THCAD torch height system looks spectacular. I don't have much personal experience with LinuxCNC, but I was very, very close to swapping to it for my mill rebuild. THCAD appears to be on par with high-dollar OEM THC's and the Neuron system.
I'm very happy with UCCNC for plasma (and milling) control. Very stable, and it has many built-in features specifically for plasma systems. I'm not a fan of Mach3, but it mostly works.
THC - The PriceCNC AVHC-10 is only available through Xtreme Plasma now. I believe they bought out PriceCNC earlier this year and while they will sell you an AVHC-10, Xtreme will not support the THC unless you purchase their machines. That said, I think it's the best stand-alone THC short of the Neuron.
The Neuron Lite is, quite frankly, awesome. Spectacular control of the torch, tons of features, extremely well integrated with UCCNC software. The downside is it's expensive. And you can't control the Z-axis except through the Neuron 'box' - UCCNC (or Mach3) is not connected to the Z-axis at all. Neuron 'owns' the Z-axis, so to speak. Makes for a very responsive torch height control, but you cannot use the Z-axis for anything else (router motor, laser, whatever). That was why the Neron didn't get used on the last build as we want to add a quick-change router spindle to the Z-axis.
The Proma is functional. It works, it's fairly cheap, it's better than nothing, and so far it's behaved properly on the machine I just finished.
Those are the ones I have personal experience with. There are other stand-alone THC's available, particularly in Europe, but you'll have to research those yourself.
Bottom line - For someone who wants to save some money and doesn't mind working a bunch of stuff out, I'd suggest LinuxCNC/THCAD.
For someone who wants it running as quickly as possible with as little fuss as possible, I'd suggest UCCNC/Neuron or UCCNC/Proma (if you need the Z-axis).
LinuxCNC is more capable than UCCNC (and UCCNC is more capable than Mach3), but LinuxCNC has a steeper learning curve.
Ok, that's enough. Go do some research and CAD modeling!
-Ralph
