Help choosing power supply for plasma table build

I'm looking into building a plasma table and am considering what plasma cutter to use. I have some experience with machine design but this will be my first foray into plasma, of which I just have a basic theoretical understanding. I'm looking to build something that will see semi-commercial use, but budget is a priority.

As far as integration into the motion and height control systems(I know I will be working THC in but have not decided on the hardware for that,) what things should I be looking for in a plasma cutter? I see some that are labeled as 'CNC enabled' but I can't tell what exactly that means and how necessary that is.

Apologize for the relatively broad question but I am more looking for some experience from you guys that have pieced together your own systems. i.e. what you looked for in a cutter, what you might do differently, etc... Please let me know if there is more info I need to provide to make it a more answerable question. Thanks!

thickness of material would be first question. If 3/8 or better is standard then you want the hd units. If I was to buy a plasma table it would have a drill head on it, drilling is faster-better-stronger-cheaper than burning. If you have a forklift have the table like Komatsu with forklift plate loading capability.

Hypertherm.

Second the recommendation of Hypertherm, the 45XP will pierce up to 1/2". A 65 gets piercing up to 5/8", an 85 increases it further. Piercing is what most of the cuts are going to require. Bought with the machine torches, they come with the needed round 14 pin cnc interface connection. If memory serves me here, I think there are 7 connections you need to feed to the THC coming out the connector on the power supply, one of those being a ground. Having just finished my build, some of that stuff is fresh I'm my memory. I went with a TMC3in1 THC board with the required ESS smooth stepper board plus an expansion board to give me more connections. And of course I used Mach4 for the control of both boards and the post for SheetCam. Warp9 has all those mentioned. Don't even consider Mach3, those pieces just won't work well with it.

I'd recommend going with the expansion board as the limit switch connections on the THC board are real limited for that purpose. You'll need limit and home switches as well as a probe input. Mine has all those. The CNC4PC's C25S is the only expansion board I'm aware that fits the other two boards. You can purchase all 3 boards as a combo from CNC4PC, but you'll have to go to Warp9 for the plugins, screen set and other software pieces. Warp9 is the official support for the THC and their control board the ESS.

If your table is going to be a full size table, I'd recommend staying away from simple stepper motors to drive it. You need speed above most all else. I used hybrid steppers on all four drives, ball screw on Z and rack and pinion on X and the 2 Y drives, reduced via timing belts for the rack and pinions. I've tested mine at rapids up to 1500 ipm on X and Y, but they're now set at 800 ipm rapids. You'll most likely never see that kind of speed on Z, mine is now set at 300 ipm or 350 ipm, don't recall exactly this morning. I cut thin sheet up over 300 ipm. At those feed rates and the rapids that occur, make dang sure you use keys on the pulleys attached to the motors. Don't rely on set screws alone. Not a big deal on the Z motor, just use a quality coupler there to the ball screw. I direct drive that.

I designed my table over a couple month period, shopping for the pieces I decided to buy and designing around them. They came from a large variety of vendors, I never found a single source for all of them. But I machined a large amount of the parts. Hate to think of the cost without me doing that. I've heard numbers tossed around out there on what people spent, some of those might have been better off just buying the whole thing they were that close to prices I see on the web. My build was under 5 grand, probably hovering around a tad over 4 grand not including the plasma unit as I had that already. Nearly a grand of that was the machine torch and consumables I bought, I had a hand held torch originally. Don't make my mistake there and just get the machine torch right out of the gate. I paid to have my first set of slats sheared too and had them bend me up a pair of Y rail covers to keep the crap off the v rails, that wasn't cheap.

Hope that helps ya along with your build. Oh, one other thing, you want the floating torch mount. Start out knowing that, the break away mount, meh, might be more trouble than it's worth. I don't have a break away. I program my starts and stops to avoid tip ups. That's worked so far. Plus I lift the torch maybe a bit higher in between to avoid any as well.

The mention of a drill on the machine is a good one. I did consider that, but in the end I abandoned it. I have a punch press so use that for small holes. I was going to use one drill size or a spot drill for everything, mount a straight drill body and use a relay to turn it on and off. I got tired of designing and wanted to get to building, but did consider a drill that fit in place of the torch for that. Never found that particular drill. Now I can see a spot drill wouldn't work out that well as the height of the slats is a continual moving target. But a pilot drill would.

One thing that would be handy and is on my to do list is laser led light cross hairs for the center of the torch you can turn on and off to indicate to set the torch to your material corner. I didn't consider that until my torch mount was designed and machined. May make another mount to incorporate those.

Hypertherm is pretty much the industry standard for plasmas.

Hypertherm, hands down

Bob49 said:

. Warp9 is the official support for the THC and their control board the ESS.




. Oh, one other thing, you want the floating torch mount. Start out knowing that, the break away mount, meh, might be more trouble than it's worth. I don't have a break away. I program my starts and stops to avoid tip ups. That's worked so far. Plus I lift the torch maybe a bit higher in between to avoid any as well.

.

Click to expand...

Bit cornfused here.

"floating torch mount" is what ?

Several versions out there, mine is on two small linear rails. Allows the torch mount to freely slide up and down some, but still have a semi rigid down position. In that travel there will be a probe switch. While Z is moving down, the torch first touches the sheet. The floating mount allows more downward movement until the probe switch is triggered. Once triggered, Z reverses a predetermined amount that gets the torch just in contact with the sheet or a thou or so above it and zeros the dro. Now the control software knows where the sheet is for that particular cut. That process plays out for every cut. Happens before any Z control by the THC and just prior to the pierce. Piercing needs to happen a set height above the material. On mine and with most HT torches that gap is .15".

Another option is an ohmic sensor, more elaborate than the floating mount. Mostly used on thinner sheet that might flex away from the touch of the probe. And mostly a floating mount is used as a backup to the ohmic sensor. One big reason for these sensing systems is the bed is an ever changing Z height, as the slats get cut through they warp. So what was a given height moments before might be some thousands or more higher or lower after a cut in that area. And the sheet may warp due to the prior cut, or never was flat to start with. Or the machine bed isn't flat and parallel to the gantry or rails. Lots of reasons. Hope that makes sense, took me some time to figure all that stuff out before starting my design. The floating mount is in addition to the travel of Z, mine has 6" total travel, then a back travel of the floating mount of maybe 3/8" stop to stop. Probe triggers at around .09" of travel of the mount but needs about .120" reverse to bring the torch up enough to just touch the sheet.

Sorry for the late reply all- Wasn't getting notifications for some reason. Hope everyone is enjoying their holidays.

All- The Hypertherm recommendation is pretty unanimous both here and everywhere else I read, but I will have to see where my BoM lands on price before I consider getting one. I seriously doubt I will be able to afford one though.

Bob49- Thanks for the detailed response. Since I'd originally posted I have made a few more decisions on the build but could still use a little more clarification on the power supply side and definitely wouldn't mind your opinion on some others.

For anyone reading this down the road, finding a comprehensive source of info was really hard, but these two links were indispensable in answering some questions: Linux CNC Build Tips Thread & Linux CNC Plasma Primer

As you can guess, I'm all but decided on using Linux CNC. Mesa 7i76E daughter card, THCAD for torch height control, hybrid stepper/servos(Though I'm on the fence on using hybrid for Z axis- Let me know what you think bob), 6mm belt drive on XY with linear rail and lead screw on Z. I might just use the frame with ball bearing wheels on that as I'm using aluminum extrusion for most if not all of the frame. I was set on using a more traditional floating head with limit switch but ohmic is something I'm starting to consider. THC is where I could still use some clarification on plasma power supply though.

From what I understand, the THCAD is a frequency to voltage converter that sends the torch voltage signal straight to the motion control which then sends the offsets directly to the Z axis driver, as opposed to handling the Z offsets with software. So what I'm still trying to figure out is if that connection from THC to the torch is made through the CNC port on the plasma cutter, or if the CNC port is obviated because of my THC hardware setup. So I guess what I am asking is- What is the typical pinout for a CNC port on a plasma cutter?

Side note- I'd never considered putting a spindle on there for drilling. That's a really interesting idea. I'd have the extra I/O's so I guess that's definitely something I can add on after....

TheWolfOfWalmart said:

All- The Hypertherm recommendation is pretty unanimous both here and everywhere else I read, but I will have to see where my BoM lands on price before I consider getting one. I seriously doubt I will be able to afford one though.

Click to expand...

I would do all I could to get a Hypertherm, I can say the cut quality I get from my older 45 is excellent. In comparing my results to a friend using a non Hypertherm torch, there's no comparison. Mine is way better. Part of that may be due to my THC, he doesn't use one. I do know he's on his second non Hypertherm torch in search of better cut quality.

TheWolfOfWalmart said:

As you can guess, I'm all but decided on using Linux CNC. Mesa 7i76E daughter card, THCAD for torch height control, hybrid stepper/servos(Though I'm on the fence on using hybrid for Z axis- Let me know what you think bob), 6mm belt drive on XY with linear rail and lead screw on Z. I might just use the frame with ball bearing wheels on that as I'm using aluminum extrusion for most if not all of the frame. I was set on using a more traditional floating head with limit switch but ohmic is something I'm starting to consider. THC is where I could still use some clarification on plasma power supply though.

Click to expand...

I don't know anything about the Mesa products other than I've heard good things on them and they are less expensive than the boards I use. I didn't learn of them until after I'd bought my boards. I also know nothing on Linux. But my friend uses Linux CNC and he's happy with it. My motion system uses V-Rails for X and Y, 15mm belt drives for those two axes and ballscrew and linear rails for Z, with additional linear rails for the floating torch mount. The belt drives use 3:1 or 3.2:1 reduction, can't recall exactly right now. I bought those 3 belt drive spindles and bought the rack gears, V-rails and V-rollers. Built everything else for X and Y axis. One thing you want to make sure of is there is very little slop at the pivot of the motor plate. You want the pinion gear and rack gear to be in good alignment. Lots of builds I've seen used bushings at the pivot, I used two bearings. That resulted in virtually no slop at those pivots.

TheWolfOfWalmart said:

So I guess what I am asking is- What is the typical pinout for a CNC port on a plasma cutter?

Click to expand...

The CPC port on a Hypertherm torch has arc transfer, plasma start and the feed from the voltage divider. My THC needs all of those. Not sure what a Mesa THC requires. My take on THC is you want the torch height controlled via hardware only. Those minor adjustments need to happen quickly. My THC feeds the Z movement directly to the motion control board (the ESS in my case). Z then responds based on the motor settings in Mach4. Any other control of the rapid rate is ignored. So the base motor settings are critical to proper operation.

With the gear reduction on X and Y, my motors are set up for 800 ipm rapids and 40 for acceleration. Z on the other hand wouldn't come close to operating with those settings. Recall the 3:1 reduction on those two axis, Z acceleration is about 1/3 of those, maybe set at 12-15 with 300 or 350 rapid rate. Otherwise the drive for Z will fault at the rapid movements commanded by the THC. I did have to add a braided copper shield to my torch cable, I was getting problems from the emi/rfi from it at times.

I used hybrid steppers on all four drives and have been happy with them. Remember you want speed out of this machine. You need good acceleration out of the corners of the cuts. My motors run up to 3,000 rpm, I went with NEMA 34's for all of them. You want the motor settings right on the ragged edge, take them to failure then dial them back. The reduced settings on the Z motor won't have any effect on motion during the cut as it's not being commanded by G-Code. Outside of touch off, pierce height and cut height of course. All other motion for Z is coming from the THC.

Think I already mentioned you want keys on the pulleys to avoid spinning of them on the motor shafts. Don't rely on set screws alone so buy motors that are slotted for keys. I bought the motors and drives off an ebay seller in Texas. Those give me encoders in the motors for closed loop motion. I run limit switches for all the axis with the probe switch for the floating torch mount.

On the floating torch mount, you want that regardless of ohmic sensor or not. I had intended to add ohmic sense after I got things running, but now I'm undecided on going ahead with it. The main point of ohmic sensing is to avoid material deflection at touch off. While I know I get some minor deflection on thin material, my 2" slat spacing does help to minimize that. I've been cutting mostly 16, 18 and 19 gage steel and I can say the results are most excellent and very repeatable part to part. My floating torch mount allows for a semi soft touch to the material. My thoughts today is between the slat spacing and a light touch from the torch on my setup, I'm not going to do the ohmic sensor. But that's not set in stone.

Good luck with your build
Regards
Bob