With respect to plasma cutting, not much of anything. I was cutting at full speed book values and the cut quality was very nice. My want to upgrade was more with respect to the router side. I had a 24"x24" mpcnc for that but I wanted to step it up a bit to support all the business I’ve gotten with my plasma cutter to make some complimentary wood/metal products. With just a few craft fairs and a couple of large sign orders I was able to mostly pay for the upgrade, which is crazy thinking about where it all started.
By going 48x96 I am splitting it into 2 48x48 sections, one for a spindle and one for the plasma.
I’m at the point now where I’m (over)thinking routing my wiring. I know most people route wires through there stainless tubes, and from inspecting your image gallery it looks like you did too? If so did you ground the stainless tubes? Otherwise I’m guessing the tubes make pretty good emi antennas for the plasma… but maybe it doesn’t really matter if you’re not trying to monitor limit switches when firing.
Yes, I routed the far side Y and Z motor cables through the stainless tubing. The wires themselves were shielded. I did not ground the tubing though I suppose you could do that as well (only on one side, as with all shielding, else you will create a ground loop). If the switches are set up as homing switches only, I believe they are inactive outside of the homing sequence. However, if they are limit switches or shared homing/limit, then yes they can be triggered due to interference. What logic level are you using for all of your sensors? I didn’t have any issues at all with 24V logic and shielded cabling.
Yeah I planned on using them as homing only, no limits. I’ve just settled on how I’ll mount all of them, none of them will be mounted on the gantry anyway, they will all be attached to the table… Except for the float switch. The 2 y and z switches will be triggered by adjustable set screws that are attached to the gantry. I don’t figure the x needs any adjustability.
I’m using 24v logic with shielded wire also. I’m going to try using all mechanical switches for now.
Unless you are using the tubes as wire, the emi in the tubes doesn’t matter. Shielding those wires is a good idea, because if there is current generated in those wires, and that ends up with large voltages, it could kill the microcontroller.
What about just not including endstops? Are you including them because you are trying dual endstops? Maybe just skip them at first.
Dui had a ton of emi issues with his plasma. I think it may depend on the equipment of the plasma cutter, but even the motor wires are susceptible to large enough emi.
The tubes, steel table, enclosures, etc. all act as emi antenna when the plasma torch fires. That’s why the shielding and even the table itself has to be grounded, and some even have to drive a 8ft grounding rod through the slab right next to the table.
I’m just using homing switches, no limits, so I’m not too worried about them during a cut. So I could probably get away with unshielded wire for the switches if I wanted to. The inputs on the control board are all optoisolated and should be protected anyway.
Cool. I’d like to see them provide the option of using a floating torch head switch and not just ohmic probing. I’m also interested to see the thc schematic they come up with. I’m guessing they is you?
Hello!
I am interested in building my own Lowrider Plasma and am doing some research for now. There is a ton of information contained in this thread!
I am probably missing something obvious, but why is a THC necessary when a floating torch holder is used. Isn’t it one or the other?
Thanks
THC, or torch height control, is an active component in the negative feedback looping controlling torch voltage vs nozzle to work piece distance. The arc emitting from the torch nozzle goes through the air and then connects to the workpiece. There is good correlation between voltage and the air gap, and if it can be measured then it can be input in a PID controlled feedback loop to adjust the Z axis to maintain optimal nozzle height (usually about 0.60" in most cases)
A floating Z is a passive component which usually consists of the torch mount riding on linear rails or smooth rods with a spring. The spring helps to keep the torch pressed down, but allows vertical movement when it comes in contact with the work. This is very useful for determining pierce height when you move to a new location. Your bed may not be level, or the material may have warped so we need to determine exactly where the material is prior to piercing. Piercing even 0.010" too low can cause molten metal to blowback on to the nozzle, creating a short and ruining the arc quality. For highly tuned plasma systems the torch body should never touch the work outside of initial height sensing (IHS). The cut height is precisely controlled via the THC to maintain the best cut quality. If the torch is too high you will get topside beveling; too low and it will put a bevel on the underside.
There’s a lot of great information on plasma systems on the plasmaspider forum.
Unfortunately…I’m not. However, is there a functional solution that could be applied to the MPCNC / Lowrider project? And yet it is not very expensive to implement.
Define expensive. The solution that @uthayne found in his build here is about as cheap as it gets for a “professional quality” THC solution, it’s a $69 card. The next cheapest solution I’m aware of starts at $300, I think you can plug it right into a standard mpcnc/lowrider build that uses marlin/grbl but by its nature it can’t perform as well as that $69 card that’s fully integrated with the motion planner.
Thank you to everyone posting in this thread. It’s been a huge inspiration. I have a lowrider2 running on linuxcnc Plasmac through a parallel port BOB($14). I’m using TB6600 and nema17s. What values do you have in the stepconf? What is your top speed? I’m not super sure my X and Y are correct and I’m positive my Z is out of wack. If you just post your .ini file I can probably decipher things from that without you having to open the stepconf.
