Saw Uses CV or CC Power Supplies,... 200 to 1,500 A, 28 to 44 V, at 60- to 100-percent-duty cycle. Automatic units commonly use up to 1,500 A on one wire. Cv welding machines that offer variable-slope control give the welder extra adjustability, and can extend the usefulness of the machine to weld a range of material thicknesses and types.Selection of Power SourcesWhen choosing a power source, start by checking NEMA specs. NEMA Class I arc-welding power sources deliver rated output at 60-, 80-, or 100-percent-duty cycle: Class II units, 30-, 40-, or 50-percent; and Class III, 20 percent. First consider capacity and kind of current needed for the job. Rely on the manufacturer''s rating as being conservative: don''t buy more capacity than needed. Choose low--duty-cycle machines only for maintenance or for intermittent welding. If portability is important, consider inverter units.

THE MOTORMost hermetic compressors use induction motors cooled by either liquid or suction-gas refrigerant. Induction motors have copper windings that, when alternating current is run through them, create the magnetic fields that cause the motor to turn. These copper windings are bulky, adding size and weight to the compressor.Two-pole, 60-Hz induction motors operate at approximately 3,600 rpm. A higher number of revolutions per minute can be obtained by increasing the frequency. Compressors that require higher shaft speeds tend to use gears. While gears are a proven technology, they create noise and vibration, consume power, and require lubrication.The magnet-bearing compressor features a synchronous permanent-magnet brushless DC motor with a completely integrated variable-frequency drive (VFD). The stator windings found on conventional induction motors are replaced with a permanent-magnet rotor. Alternating current from the inverter energizes the armature windings. The stator (excitation) and rotor (armature) change places. No commutator brushes are required. The motor and key electronic components are internally refrigerant-cooled, so no special cooling is required for the VFD or the motor.

Environmentalists have been quick to point fingers at chip mills for devastating forestry practices. But the industry insists it''s "out of the loop" concerning timber cuts, since operators purchase their supply from private landholders. Industry officials are so infuriated, many refused to comment. The line connecting chip mills to clearcuts and destructive forestry isn''t a straight one, but it is visible. Dean Carson of the South Carolina Forestry Commission argues that chips can be transported more efficiently, using less energy, than large pieces of timber, and mills can utilize the whole tree. But processing the whole tree is exactly what has brought the mills under fire: because lumber is chipped into one-inch pieces, any size scrap of timber will do. With new markets opening up for treetops, undersized trees, and forked or crooked specimens, landowners have added incentive to clearcut a site for quick profits, instead of harvesting selected trees to be cut into boards. And timber previously left behind to continue maturing, or that provided wildlife habitat or eroded to replenish soils, now finds itself in the steely mouths of the chippers. A 1998 U.S. Forest Service report says clearcutting accounts for 13 percent of logged land in the South. And because the chips are needed for everything from rayon and plastics to particleboard and paper, chip markets continue growing. Timber giant Willamette Industries says chip mills allow landowners to merchandise otherwise unusable trees, discouraging forestry practices like "high-grading" (cutting only the healthiest trees). "Clearcutting is often the best tool to assure a rich, diverse forest," claims Willamette''s web site. "Many songbirds and other types of wildlife require open areas for nesting and food gathering."

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