50 SERVO 09.2016
An Introduction into Plasma
I have been doing a great
deal of research for a series of
books I plan to write over the
next couple years, and
thought it would be a good
break from the KReduCNC
project to touch on some of
By Michael Simpson
It is my hope that this article may help some of you who have been looking into purchasing a plasma cutter. In all of my CNC projects, CNC plasma cutting has been the most challenging. Just about anyone can operate a handheld plasma torch, but making
quality cuts on a CNC is another level. You are dealing with
more than just the CNC mechanics. You have to deal with
lethal voltages and currents. You have heat so hot it can
throw molten steel several feet in every direction. There are
grounding issues and shielding issues. Let’s not forget that
a high end plasma cutter can cost as much or even more
than the CNC itself.
I find it easier to tackle larger complex projects by
breaking them down. That has been the approach I have
taken with my research. So to get us started, I am going to
cover just the plasma cutting basics.
How Does a Plasma Cutter
First, let me just hit on how the plasma cutter works. A
plasma arc is started by applying current (and spark)
through a gas that is flowing through a very small opening.
The arc ionizes a portion of the gas, thus making it a
conductive plasma. The gas can be argon, nitrogen,
oxygen, or even just compressed shop air.
In order to apply a current through this gas, it must
flow into or through a conductor that will allow sufficient
current to flow. When the arc in the torch is started, it is
often referred to as the pilot arc. When the arc comes in
contact with a piece of metal that is connected to the work
clamp, the current flows from the torch through the metal,
thus transferring the arc.
By spiraling the gas and passing it through a very
narrow orifice, this allows the created plasma to cut
through any metal by creating a very fine molten kerf.
There are three common ways an arc can be initiated:
This is where the tip of the torch is struck or dragged
against the stock which has a work clamp attached. With
the gas flowing through the torch, the sparks created by
the completed circuit ignite the gas, and the arc is started.
This method is employed on many very low end plasma
cutters and is not suitable for CNC use.