Re: [CAD_CAM_EDM_DRO] Re: plasma accuracy

Some time back, I designed and built a pantagraph system for two plasma heads (multiple cuts of the same shape). A simple affair on parallel arms and the operator was required to make a template of the shape out 1/4" steel and an adjustable low speed motor rotated a neodymium magnetic roller/stylus that followed the pattern and would guide the torch heads. What I remember about that setup was going through tips like there was no tomorrow. They just didnt last very long no matter what the heights were form the material. Would torch height control in Mach2 alleviate this? Also as far as the kerf went. We were getting a kerf of like .100 in 1/8" material. Anything is possible but kerfs of .010 is hard to believe. Simply due to the violent nature of this type of material removal. The experiences with those plasma torches soured me on getting involved with it again. They continued to use the machine however, I never knew if they resolved the tip failure issue as it was in another building
across town. Is this a normal result in regards to tips having to be replaced every hour or so? They were new miller machines with 100% duty cycle and they were burning approximately 90% of the hour. If I were convinced I would get better results with a CNC plasma with torch height control I'd definitely consider building one.
Ron

caudlet <thom@...> wrote:


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Graham Stabler"
wrote:

>
> > There is a guy who made his own power supply for a a little over
> $100
> > bux.
> >
> > I hear that a standard machine can do 20 to 45 thou as a standard
> > kerf and the Hypertherm fine cut can do less than 10 thou.
> >
> > If one was to cut lots of shim, say for production, I would look
> > seriously at a low power laser.
> >
> > Dave
>
> I would be interested in hearing about that guy. I have a 50W C02
> laser but micro plasma seems a cool idea to me and very

homebrewable

> in comparison.

The secret to plasma cutting (and I would like to see a standard
machine that can hold .025 kerf width) is NOT the power supply. It
is just a rather crude constant current source that has a an open arc
voltage of around 200 Volts and cuts at about 70 to 100 VDC.

The challenge is to first ionize and "ignite" the air to make the
30,000 deg plasma flame and then *control* it so it doesn't cook all
of the surrounding components. Most torchs have specially designed
swirl chambers to spin the air as it exits the tip. The torch handle
and it's design are what largely controls the quality of the cut.

Hypertherm makes a "Fine cut" series of consumables for some of their
torch models that will hold .025 under perfect conditions, but .010
is doubtful.

Precision plasma (different technology and $$$$$) uses shielding
gases other than shop air and uses oxygen (I think) for the plasma
and will do some fine cutting.

Using a standard plasma to cut foil is like driving a tack with a
sledge hammer.

I'm real happy when my torch holds a .062 kerf and depending on the
wear on the consumables it can climb to .080 or higher. Pierce points
can be double the cut kerf in diameter. I try to plan my cuts so
things that need detail are cut first on a new set of consumables.






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