The plasma cutter works in the beginning like an arc welder. An electrical current establishes a concentrated arc, the heat source. As the heat melts the metal, compressed air is injected into it. This "jet stream" blows away the molten metal as the hand-held torch moves along. A single knob adjusts the heat and air settings for various metals and thickness.

Used on autobody sheetmetal, the cut is narrow and clean. The paint is not burned more than 31/432 inch on each side. This same machine will cut a 31/48-inch-thick steel plate. In fact, a plasma cutter will cut any material that conducts electricity, such as aluminum, steel, copper, stainless, or brass. I have used it to cut an aluminum sheet to make an air cleaner and also to make suspension brackets for a street stock. In short, this is a very useful machine.

How To Use It

As with any machine, some skill is necessary. With the Miller Spectrum 375 Cut Mate, very little skill is required.

A plasma cutter requires a source of compressed air and electricity. This one can be used on either 110 volts or 220 volts with the flip of a switch, but 220 is preferable. An air compressor that will keep up with a touch-up-type spray gun is sufficient. Only 4.5 cfm at 60 psi is required.

With the machine plugged into the selected electricity, using somewhat more air than you can blow into a Breathalyzer, turn on the switch. The ground wire must be attached to the work piece like a welder. It will actually work without the ground but not nearly as well. With the torch in hand, hold the tip near vertical and touch it to the metal you want to cut. When you pull the trigger, things happen fast. If you have used an oxyacetylene for a while, you may have a tendency to move too slowly. On body sheetmetal, the torch will cut at a faster speed than you can accurately follow. Thicker metals, of course, require slower travel while cutting.

There are no special needs when cutting aluminum other than to adjust the knob, if necessary. Aluminum has such a rapid heat transfer that more heat may be needed. I cut out a 10-inch circle of 0.095-inch aluminum. Immediately, I picked it up bare-handed on the opposite side from where I finished cutting.

As with anything that throws sparks, eye protection is a necessity. The eye protection need not be the same as TIG welding, so medium dark safety glasses are sufficient.

To begin a cut on a flat surface, angle the torch slightly away from you. This will keep sparks from flying in your direction. As it begins to cut, bring it back to vertical.

Cutting is always easier and cleaner if you can use a guide. A steel bar clamped in place makes a good straight cut guide. I have used things around the shop such as wheel rims for curved or round guides.

Once a part is cut out, it might need a little cleanup on the backside. When the plasma cutter is adjusted properly for the metal and thickness, very little cleanup is needed. Often, just tapping the cut face with a small hammer removes all the slag. This is easier than getting out the grinder.


The TIG process makes quality welds on steel, alloy steel such as 4130, and on aluminum. The TIG machine allows a soft start and soft stop. This prevents heat shock to the metal. Heat shock is detrimental to 4130 alloy welds.

The plasma cutter provides far better control of the cut area than a torch. It cuts any material that conducts electricity. Also, it puts much less heat into the part being cut, greatly reducing warpage.

Again, I can't teach you everything about using a TIG or plasma cutter in this article. My intention has been to introduce you to these tools and demonstrate what they can do. Hands-on experience will further this education. I recommend Welder's Handbook by Richard Finch. This book, available from Speedway Motors, covers all of the above in greater detail.Contact Sleepy at

Miller Electric Manufacturing
Speedway Motors
P.O. Box 81906
NE  68501