New Plasma - stepper or servo for Z

I am in the process of ordering parts for a new machine I am building.
With Plasmac. would it be better to use a stepper or servo for the Z, and why?
I am using servos for X and Y
I will be using 5i25-7i77 with a thcad card

Thanks Bob

I suspect you would be better off with a 7I92M+7I77 for EMI reasons
_if_ the PC is not built into the same box as the 7I77

PCW wrote: I suspect you would be better off with a 7I92M+7I77 for EMI reasons
_if_ the PC is not built into the same box as the 7I77

The PC is in the metal console with the 7i77. I am reluctant in trying the ethernet modules. I've always used 5i25 and have never ever had a problem. They just work....

Overall we have had fewer problems with Ethernet cards than PCI,
mainly related to dirty PCI contacts ( user plugs PCI card into slot of old PC
that has been vacant and accumulating grime for 10 years... )

PCW wrote: Overall we have had fewer problems with Ethernet cards than PCI,
mainly related to dirty PCI contacts ( user plugs PCI card into slot of old PC
that has been vacant and accumulating grime for 10 years... )

OK, turns out the same price as plug n go kit when you buy the db25 cable.
Will have to buy a nic card though also. Not mentioning compiling, which I don't have alot of luck with....lol


I have a few days to think about it before I order.

If the 7I77/connecting cable is in the same box, there's not as much
advantage in using Ethernet.

Where its nice is when the PC is in a control panel some distance
from the drive/electronics box

You should not need to compile anything to use Ethernet (just use the Stretch.LinuxCNC ISO)

Ok, I think your reasoning is sound for most CNC machines. For plasma you want all the isolation you can get between the table and your control computer. I realize PCW, the inventor of the Mesa cards, may differ but for plasma use an Ethernet card with its's own power supply! I have never had a hiccup with my 7i76E and the only other thing I have is a THCad card some relays and a couple of opto modules. Full limit and combined homing switches, float switch and ohmic probing. I still have more I/O points available left over than I know what to do with. Full disclosure I also have a USB pendant that also works well for me.

John

I think if I was working with servos, I'd use one on the Z as well. I use a 7i76e and unlike John, I've used just about every input on it. I think I've got about one left. Mainly becasue I chose to use a wireless pendant with a receiver in the control panel and seperate home min and max limits on every joint.

You don't say what plasma cutter, how big the table is and if its HF start or not. My neighbour at work has a new HF start Hypertherm 200amp machine and commercial table and has been plagued by problems with his arcOK circuit faulting and stopping cutting due to what my resident HF electronics expert says is due to basic design faults that a $17 part could fix. Thats why I like the ethernet cards..... and the plasmac ohmic sensing circuit that Islander designed.

Rod, do you have a link to Islander's ohmic sensing circuit?

rodw wrote: I think if I was working with servos, I'd use one on the Z as well. I use a 7i76e and unlike John, I've used just about every input on it. I think I've got about one left. Mainly becasue I chose to use a wireless pendant with a receiver in the control panel and seperate home min and max limits on every joint.

You don't say what plasma cutter, how big the table is and if its HF start or not. My neighbour at work has a new HF start Hypertherm 200amp machine and commercial table and has been plagued by problems with his arcOK circuit faulting and stopping cutting due to what my resident HF electronics expert says is due to basic design faults that a $17 part could fix. Thats why I like the ethernet cards..... and the plasmac ohmic sensing circuit that Islander designed.

Its a 5X11 water table I am building and I will be using Hyperterm 105 with the CNC torch.

I'd be interested in looking up the ohmic sensor you used.