Setting up a plasma cutter and looking for some help.

islander261 wrote:

You say that you have two axis moving now. What type and thickness of material do you want to cut? What speed and acceleration can you get now? If you don't have a working LCNC configuration how are you testing you axis servos? Did you have the Teknic's sales engineer size your servos for you? If not you most likely didn't get the correct size for your table, it is much harder to correctly size servo motors for good performance than steppers. They may work now but the overall performance will never reach a servo driven systems potential.

John

The motors are oversized torque wise as compared to the original ones allen bradly had on it. It has been a while so I don't recall the exact specs of the old motors.

Long story short we started this project back mid 2018 when we got the motors. Due to several reasons the motors got physically installed but the project got abandoned until I got back on it about a week and a half ago.

A bit of history on the machine. At one point it was a water cutter with an Allen Bradley control.(Bubble memory anybody?) At some point prior to my joining the company in 09 it got converted to a plasma cutter. It was using a Delta Tau PMAC ISA board connected to the original DC servo drives. This worked but was always cludgy. Well the drives started dieing and I could not get them back working. Cost wise it seemed better to just get new motors and start over. I could not make heads or tails out of the pmac board and decided to go with something like linuxcnc or mach3 or the like.

Thickness? Not sure but the plasma side of things worked fine for our purposes when it used to run. And unless something has broke in the ~5 years it has sat it should be fine.

As for speed it is currently doing way more than we will need. Don't see why accell is not as well but can't guarantee that.

I have a working configuration so much as running the step config tool as an xy machine and getting the step/inch dialed in. Linux cnc will move the machine just fine. Still have to get limit switches wired and the plasma side of things wired to LCNC but that should be it.

One note. The clearpath servos have an auto tuner that you run once they are installed. As I understand from other threads around here this is fine but using the rest of the software side of the motors kinda goes against LCNC's purpose so I am just using them in S/D mode. Still better than steppers for both torque and position as assuming the steps make it to the motor it won't loose them.

Sorry for the rambling. I keep re-reading your post to see if I missed a question and have answered them all out of order.

islander261 wrote:

I used the Torchmate AVHC for Zaxis control for years and as Rod says it will not work correctly with the PlasmaC branch without serious hacking. Further more depending on the actual firmware version you have the cornerlock feature may or may not work even though the input is there. If you still really want to use the TM lifter assembly (Z axis mechanics and drive) the very expensive Smartmotor on it can be programmed to work as a simple step and direction drive like your Clearpath servos. The TM lifter is a POS really so build or buy a better one.

Just spend the money and buy a Mesa 7i76E and THCAD boards, you've already splurged on good servo motors. In the end you will be much happier with the results, actually no comparison really. Did I say the TM AVHC system is a true POS compared to the PlasmaC standard?

John

I am definitely going to look into getting a motor for the lifter/repurposing the current one. Everything I find + what you are saying leads me to believe it is not the greatest.

The mesa thcad board looks real tempting. Not sure if I have to get the i/o board. Maybe. I likely have the stuff to add a second parallel port for the extra I/O if I need it.

One random thought and a quick search later.
Ok so it looks like the Torchmate AVHC actually sells for a fair bit on ebay. Selling it and going the mesa route sounds better and better. Now to figure out a good lifter and motor here.

People that have old TM systems that they want to keep running really value those old AVHCs. The smartmotor alone will fetch $350+ on ebay. The smartmotor it's self is a clever bit of kit and is still worth quite a bit, the rest of the lifter mechanics are a POS.

You are already using LinuxCNC to drive your table so you have access to all the axis velocity and acceleration information from your .ini file and by using halscope.

You are much better off (even though Tommy will disagree) to use one of the Mesa ethernet boards to provide galvanic isolation between the PC and the rest of your controls with a plasma cutter. An added side benefit is much relaxed latency and jitter tolerance because the FPGA does all the step timing. With the exception of Tommy most of the active PlasmaC users are using the THCad and either a 7i76E or 7i96 card for their machines, the majority of the actual cutting while testing PlasmaC was done using the 7i76E and THCad.

Get all your homing and limit switches working, while not an absolute requirement the functionality makes for a much easier (less dependent on operator skill and attention) machine to use when doing production use.

John

Im not getting scared off. I might ignore what people say but I am hard to scare.

Looking at my torch it gives 3 voltage outputs. Full voltage, 120V and 24V. As I understand I need to setup a voltage divider and use the 10V mesa card on the 24v output?

Any recommendations on a lifter setup? Not a real big fan of the one that come with the torchmate even before I started researching it. Too much play. I assume a stepper will be fine there as is does not need tons of torque.

Ok so looking more at the manual it seems I have a divided arc signal on the cnc connections as well that can be set from a 1:50 to a 1:16.7 ratio. Can I use this directly to the mesa board?


1drv.ms/b/s!Anw0aD8CF6Z_huIbtN0Cd2dSG7a9VA?e=HXL5aT is a pdf I scanned of the cnc connections. I'll let somebody more familiar with plasma figure out what would be best. If it matters the back of the machine lists 180v as the top end voltage.

I use a slightly modified one of these:

www.veloxcnc.com/xz-za-series

I added a homing switch at the top of the travel and longer bearings (ebay specials) to the floating part. I also use a home made magnetic break away torch mount. These aren't cheap but I needed to replace the TM AVHC POS, at first I still used the smartmotor and the box then finished switching to LinuxCNC.

John

I am thinking about using ohmic sensing. As I understand it i should be able to just run a wire from the torch head and one from the ground and treat it like a limit switch right? With an added relay that only connects it during probing so as not to feed back to the electronics. Is this understanding correct and natively part of plasmac? Slow feed down till it contacts, back up a touch and then real slow feed till it touches again?