Q: What do I need to know to select a plasma cutter?
A: You need to know what thickness of metal you will routinely cut, the maximum thickness you might cut and how fast you want to cut. These factors relate to cutting capacity. Many people judge a plasma machine solely by amperage, but remember that total output power (in watts) equals amperage times voltage. For instance, Miller's Spectrum® Thunder and a competitive 12-amp unit both feature a built-in air compressor. However, the Thunder is rated at 110 VDC (1,320 watts) while the other is rated at 70 VDC (840 watts). The Thunder delivers 57 percent more cutting power and provides a quality cut on 3/16-in. steel. The other unit only cuts 1/8-in. steel.
Q: How much power do I need to cut a given thickness of metal?
A: The cutting capacity of a particular "size" plasma machine varies greatly by manufacturer. The following table indicates the maximum cutting performance of Miller's hand-held units, which equal or exceed all competitors:
Machine Output Quality Cut Rating
12 A @ 110 VDC 3/16 in.
27 A @ 90 VDC 1/2 in.
50 A @ 110 VDC. 3/4 in.
55 A @ 110 VDC 1 in.
80 A @ 140 VDC 1-1/4 in.
100 A @ 120 VDC 1-1/2 in.
Q: How do I determine cutting speed for a given thickness of metal?
A: Miller provides a chart that shows the cutting speed of every machine. Miller also qualifies cutting capacity with three standards: rated cut, quality cut and sever cut. "Rated" means you can manually cut mild steel at 10 IPM. With a "quality" cut, you can cut thicker material, but at a slower rate. The edge of the cut is still smooth enough so that cut pieces can be welded together with little, if any, grinding. A "sever" cut rating pushes the machine to its maximum. Cutting speeds will be very slow and the cut requires significant clean-up. Cutting speed varies greatly between brands. Tests on a mechanized cutting table show that the Spectrum 2050 can cut 1/2 in. steel at 38 IPM with an extended tip and at 30 IPM with a drag shield. Some competitive units of the same amperage only cut at 24 or 28 IPM.
Q: Can I run a plasma cutter off 115 V primary service?
A: Yes - Miller recognizes that many job sites, particularly with HVAC and maintenance, only have 115 V outlets. The Spectrum Thunder and Spectrum 375 CutMate™ operate using 115 or 230 V power. If your input circuit has a 30-amp breaker, you even get equal cutting capacity at both voltages. Both these machines feature 15 percent line voltage compensation. This wider operating window allows you to use a longer extension cord with less chance of nuisance trips occurring.
Q: Can I run a plasma cutter off my engine drive's auxiliary power?
A: Yes. The Spectrum 2050 cuts 3/4 in. steel when connected to an engine drive with 12 kW auxiliary power (such as the PipePro™ 304) and cuts 5/8 in. steel when connected to an 8 kW machine like the Bobcat™ 225 NT. The Spectrum Thunder, 375 CutMate and 3080 also run well off engine drives, and their light weights (43, 49 and 74 lb., respectively) permit job site mobility. Note that Spectrum plasma cutters feature special circuitry that enables them to achieve full cutting power and maintain a steady arc. Other units can't manage the voltage dips that inherently occur when using auxiliary power. As a result, a competitive 55 amp machine cannot cut metal thicker than 3/8 in. - that's a 133 percent loss of cutting power compared to the 55 amp Spectrum 2050. Other machines are also prone to erratic arcs, inconsistent cutting performance and excessive circuit board failures.