newbie with cnc plasma toy

[cidteach]

hello all,

i have a weird situation and would like some input.
my school has been given a wood routing machine, legacy 900. it was provided with mach3, lazycam and no real support. after playing around for 2 weeks, i got it running and am able to run a program (tracing the roadrunner sample with a marker on paper).

this machine is rather small, but i have a small chinese plasma cutter (ramsond cut50d, supposed 50amp cutter) the plasma cutter performs decent for basic chopping, and is light weight and very portable.

I teach machine shop, have some good tools and machinery, lathes, mills, cnc mill. i would like to adapt my plasma cutter to this small router for small parts making and instructional purposes in my shop.
however the plasma seems to be contact start, not auto. also, not sure how to connect the plasma so that mach can automatically turn it on and off.
the nice big control box for this router has all kellingcnc drivers and such - seems like a well laid out unit and package.
any suggestions on how to adapt my cheapo plasma to this small router - im not worried about the mounting of the torch, or bed for material more just interaction of mach and torch.
any help or thoughts are greatly appreciated.
tc

[jimcolt]

I would be concerned with the high frequency start of that plasma system causing issues with the drive and the controls on a machine that was designed for a non-electrically noisy device such as a router. Further....that torch has to scratch - start the workpiece.....easy to do with the torch in hand, but difficult on a cnc.

You would be better off finding a non high frequency plasma such as a Hypertherm Powermax series (Powermax30, 600, 800, 900, 1000, 1250, 1650 systems are all "blowback start"), having a strong pilot arc for easy arc transfer to the plate, without any high frequency to cause issues/damage to your electronics.

Jim Colt

[cidteach]

Jim,
Thanks for joining in on the fun! I know a better plasma would be ideal, however with a public school, specifically mine, i will see a retirement check before i see any new tools - my students sold boxes of chocolates to purchase this unit a while back, on their own initiative and time...it was quite impressive.
I was thinking of making a radial spring getup to attach to the torch nozzle to contact the metal plate and keep the torch at ~0.1" (basically trial and error). Tips are cheap and we have a bunch as well. I would really like to get this going as i have nothing better and precision is not a real concern, more just basic brackets/ornamental items for student project learning code/various cad/cam stuff.
Because this is faster and more exciting to watch than a cnc mill they are much more inclined to work and get creative. The electronics are located about 5' away from the table - although interference is interference. How are torches typically connected to a diy plasma table, via breakout boards - i believe this one has a hobby cnc C10 version if that helps.
thanks

[mlabruyere]

Hi TC,

I think the interference Jim is referring to will be picked up by the cabling running on the CNC unit. This include the control/power cables for each stepper as well as any home and limit switches the unit has installed. These will all be very close to the arc regardless of the distance the actual control unit and PC are in relation to the cutter. You could always test this with the pen you already have setup. Get a detailed design for the CNC to draw and then fire up the cutter. See if you get missed steps or the unit crashes. I would also power the plasma on a separate circuit from the PC and controller.

Matthew

[cidteach]

Thanks Matt,
I have been tracing images of NY Yanks, circles and random brackets for a few days - they all seem normal-no erratic or random errors. They are all on separate outlets due to location in the shop, blind luck i suppose. How would i be able to configure mach and the torch to communicate with one another?

as an aside, have any of you guys heard of USFIRST Robotics?? This is the 3rd year our school is participating. To see the new game, go to youtube and search for FRC Breakaway.

tc

[mlabruyere]

Hi TC,

Cool about the robotics comp....I had not heard of USFIRST.

Normally you'll need a relay of some kind. This relay connects to the BOB (break out board). The BOB has output channels that are controlled by Mach. You would probabaly connect it to the "Spindle" control.

As far as the VB scripting you will need to get it to touch of a spark and what not you may be able to use a modified "auto Z" script. I've never used a plasma before so I am not sure about all the details.

Matthew

[fatal-exception]

Hi tc,

I too have a cut50 in my shop right now and was wondering how to make the torch fire in cnc mode. I also have an older Hyperthem plasma, but it isn't powerful enough for some of the stuff I have coming up. The Hypertherm works well, I have to admit and I will buy a shiny new one once some funds come through, but for now, I want to get the cut50 working.

The 2 pole connector on the front of the cut50 is the trigger switch. You can wire this into a relay on the C10 breakout board. In mach3, set the output signal for the M3 command to the pin that the relay is wired into. (On my board its pin 16) You can easily test if its working by putting an ohm meter across the relay and switching the spindle on and off in mach 3. You should see the contact close when the spindle is on, open with it's switched off. (If you have the reverse, change the 'Active Low' setting for the output pin)

So, onto the difficulty. We were also thinking about a spring from the tip to the workpiece. I'm not sure if this will work or not, but will be pretty easy to try. If the spring is to stay in touch with the workpiece all the time, I'm not sure how it will handle sliding over previously cut kerfs.

I'm doing some work with this cutter this week and will let you know how it goes.

Paul

[fatal-exception]

Just a short update to the progress of CNC'ing the Cut50. We played around with it on saturday after getting the torch mounted and the switch wired into the break out board.

Strange things happen with the high frequency start. Sometimes it would freeze the entire computer when trying to fire, other times it would just take out the USB bus, which would require that the mouse be plugged into a different port to get it back.

The problem with the computer locking up got marginally better when we wrapped the Cut50's ground wire around the torch line, and unplugged any non critical USB devices. So that's where the problem lies as far as computer interference. If the Cut50 were our only plasma cutter, we would spend a good amount of time tweaking it to see if it could be reliable, but this little experiment makes the hypertherm look that much better, regardless of its cut limitation.

The tip dosen't actually have to touch the material, but it must be very close, probably within .01" or closer. It really didn't have any problem firing the torch when set close to the material, so we didn't try a spring from the contact tip. I think the big problem is that the tips will go fast due to starting so close.

Anyways, the Cut50 has been shelved as far as CNC goes. Just too many problems, but as a quick and dirty hand held cutter, it's pretty darn handy.

Paul

[jimcolt]

High frequency plasmas should only be used on cnc machines that are specifically hardened for this type of start mechanism. These machines send as much as 15,000 volts at a frequency of as much as 2 megaherts down the length of the torch leads....this creates an ionizing spark to get the plasma process started. generally speaking...any cnc that uses a PC for the controller will likely be affected.

You could in theory stop this RF noise issue by filtering all I/O points, enclosing the PC and drives inside metallic sealed enclosures, shielding all I/O and motor/encoder drive cables......as well as shielding the torch leads.....with one end of every shield wired to and earth ground rod. In some cases all of this works......but sometimes the RF from the high frequency circuit cannot be stopped!

Industrial CNC controls are designed to work with High Frequency start plasma as almost all Industrial plasma systems use this starting method. For PC based machines....it is always best to use a "blowback" style torch like the Hypertherm Powermax systems.

Jim Colt

[fatal-exception]

So Jim, Just a quick question, what is advantageous about using HF starting in an industrial environment?

Paul

[jimcolt]

High definition class plasma torches are designed to produce highly accurate, very repeatable cut quality....and to provide for consumable life that can be well over 10 times the life of consumables in an air plasma / portable type torch.

The non high frequency torch has a moving electrode.....because it has to slide and move....it is not as stable as a perfectly aligned fixed electrode. Further....temperatures on the end of the electrode reach 3000 degrees F......in order to acurately cool the electrode, liquid coolant is pumped inside the electrode at high pressure, low flow to efficiently remove heat. Coolant also must be routed as close as possible to the nozzle orifice...in order to allow high energy density (60,000 amps per square inch vs about 12,000 amps per square inch in an air plasma) to be developed without melting the nozzle orifice. With high frequency start....consumables alignment is far superior and the necessary cooling can be achieved.....and high production, high accuracy cutting can be done.

The large industrial systems are about 10x more expensive as compared to entry level air plasma systems.....but the parts that are cut are more accurate, higher volume, and lower cost per foot of cut.