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Author Topic: Want to do plasma on my wood cutting machine..Need guidance  (Read 4216 times)

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I have been using Mach3 for about one year now with great success. Mach3 is a great program and represents a good value.

Now I want to broaden my horizon a little. I am in possession of a brand new plasma cutter. It does not have a CNC interface but it does have trigger inputs that I could use with any controller. Here is my confusion. I am assuming a Torch Height Controller is necessary to get the initial spark started. My plasma cutter has a pilot arc starter so I could ignite without touching the cutting surface. My torch has a detachable guide to keep the nozzle a consistent distance from the cutting surface. Couldn't I just build a holder for my torch and set my z axis to the required height and just leave it there? Do I still need a THC? How do I get Mach3 to pause for ignition before moving the x and y axis'?

And the last part of my question which I don't think is a function of Mach3. Say I was cutting a 3" circle in thin steel stock. It only seems logical to me that the cutter not ignite on the perimeter of the circle but rather somewhere inside or outside of the circle to provide a really smooth cut transition. Could somebody tell me if this is an accurate statement and what this type of manipulation is called? Is it some type of offset? How do I implement it in say CamBam etc?

Sorry if any of this is too noob sounding. All help is greatly appreciated.

Offline stirling

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Re: Want to do plasma on my wood cutting machine..Need guidance
« Reply #1 on: July 30, 2010, 05:30:22 AM »
I am assuming a Torch Height Controller is necessary to get the initial spark started.
No (because of your next statement). You just need to arrange your torch to be at "pierce height" above the work and fire the torch.

My plasma cutter has a pilot arc starter so I could ignite without touching the cutting surface.
there you go - that's why you can do the above

My torch has a detachable guide to keep the nozzle a consistent distance from the cutting surface. Couldn't I just build a holder for my torch and set my z axis to the required height and just leave it there?
You could indeed.

Do I still need a THC?
Depends on how good a cut you want and how often you're happy to renew your consumables and how long before you get fed up of the "drag tip" moving the metal and ruining your part

A THC will give you FAAAAAAR superior cut quality, save you lots of cash in consumables and allways keep your torch off the work and at the correct cutting height as it travels over the warped metal. Warped as in to start with and as the heat affects it. BUT for THC to work you also need IHS - see below.

How do I get Mach3 to pause for ignition before moving the x and y axis'?
write a gcode cut prolog. OR use a CAM (I like Sheetcam) to generate your gcode and you're done. It's not just pause for ignition. It's move to pierce height, fire torch, make sure arc is good, pause for pierce, lower to cut height, commence XY. The question is: where is pierce height? for this you need Initial Height Sensing (IHS). This is often done with a floating head and switch arrangement.

And the last part of my question which I don't think is a function of Mach3. Say I was cutting a 3" circle in thin steel stock. It only seems logical to me that the cutter not ignite on the perimeter of the circle but rather somewhere inside or outside of the circle to provide a really smooth cut transition. Could somebody tell me if this is an accurate statement and what this type of manipulation is called? Is it some type of offset? How do I implement it in say CamBam etc?
Correct - it's called leadin (there's also leadout) again it's a function of CAM.

Ian
« Last Edit: July 30, 2010, 05:33:26 AM by stirling »
Re: Want to do plasma on my wood cutting machine..Need guidance
« Reply #2 on: July 31, 2010, 08:22:22 PM »
Stirling:

Thank you for the heads up on SheetCam. It seems like a very intuitive program and the price ain't too bad either.

I did download the demo version of it and began my learning process. May I ask you two things about the relationship that SheetCam and Mach share?

I am going to be flat out honest. I have not a clue what a post processor is. I have made it by in the past with CamBam and no real need to use any special processors. I notice the various processors that Sheetcam is delivered with. I of course chose the Mach3 Plasma processor for now. I don't  know what it does or if I chose the correct one. Could you give a brief idea of what it does?

This next problem may or may not be related to the above. I was attempting to do a simple heart shape cut out in steel as a test. When I load the tap file generated by sheetcam it runs very very badly. Almost like a stop motion film. There is no fluidity. In CamBam I use exact stop for these type of objects and the curves come out beautiful and exact. In CamBam if I used constant velocity the curves and fonts would sometimes be off. So now I am totally confused. What options should I use between sheetcam and Mach to get normal operation? I do remember reading about the I/J settings in Mach but it worked in the past with CamBam so now I don't know what to do. Thanks for your time.

Offline stirling

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Re: Want to do plasma on my wood cutting machine..Need guidance
« Reply #3 on: August 01, 2010, 05:32:02 AM »
Although I use sheetcam - I'm no expert and am still working my way through understanding it's details. That said basically a POST (post processor) deals with the machine specific part of the code generation process. Anoyingly, AFAIK sheetcam doesn't document the purposes, differences or subtleties of each different post. So we're kind of on our own I think when it comes to choosing one that best suits our purposes. Maybe someone else can help you better with this or of course go onto the sheetcam forum and ask - Les et al are very helpful. I chose the THC300 (because I currently use a THC300 THC) one and modified it till it did exactly what I needed.

Second issue sounds like you're using short line segments for arcs, which with exact stop mode will do a pretty good job of getting your machine to sound like a machine gun on heat! My thoughts would be that for plasma you're going to HAVE to get CV working best you can within the accel capabilities of your machine. Exact stop mode with plasma is going to be grief IMHO.