Q2
2010 Articles
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By Scott MacDonald
 Circle cutting demands precise motion control and circle cut quality will vary as the circle diameter approaches the thickness of the plate. A circle that is equal to the diameter of the thickness of the plate being cut is the minimum circle diameter possible. Cut quality will be decreased when the circle diameter is less than 1.5 times the material thickness being cut.
For Best Results:
- Slow the travel speed. Smaller circles may require a cut speed that is 50 to 60% of the recommended speed in the system cut charts. A slower cut speed will eliminate/reduce the trailing arc and allow the arc to cut at closer to a 0 degree of bevel.
- Maintain constant cut height through the circle. This may require locking out the height control. As the cut speed slows, arc voltage increases and the height control tends to drop the torch downward, changing cut bevel. (Avoid the torch height movement by locking out the height control.)
- Start the cut in the center of the circle and use a 90 degree lead-in to the circle. When the cutting table is running properly, a 90 degree lead-in will produce less distortion at the circle start point. A cutting table with backlash may produce a better result with a radial lead-in.
- End the cut by over burning the circle cut line rather than by using a lead-out. Time the cut to end just as the arc completes the circle. A lead-out or too much of an overburn will cause the arc to cut more of the outside of the circle and cause a distortion at the point where the circle cut is completed. Many CNC controls use an advanced off feature to ramp down cutting current at the end of the cut. (The use of the CNC’s advance off feature will improve circle cutting.)
Inquire how to receive cut samples at automation@thermadyne.com
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