• Always choose the lowest amperage process from your Powermax cut charts that will have the ability to pierce the material and thickness you need to cut. For example, for the Powermax125, the cut charts indicate that you can pierce 5/8” steel with the 125 amp, 105 amp and 65 amp processes. Because the 65 amp process is the lowest process capable of piercing 5/8” steel, that’s the one you’ll want to choose for the best hole quality. The primary reason the lower amp processes work better is because the machine speeds stay lower, allowing the torch height control and the motion control to react well with the characteristics of the plasma arc.


• If you use the 65 amp process on 5/8” steel, the book specs for best cut quality look like this: Pierce height (critical) .24”, Pierce delay 2 seconds, Cut speed 23 IPM, Cut height .06”. Using these specs exactly as written in your owner’s manual will get you the best cut quality when using 65 amp shielded consumables at 65 amps. Increasing the amperage will rapidly wear the consumable parts, and is not recommended.


• Design your hole with the start point near the center. This will allow the height control to:

1. Find the surface and retract to the correct pierce height, which again is .24” on 5/8”.


2. Ensure there is no movement on the X, Y, or Z axis until the 2 second pierce delay is complete and the arc has fully penetrated the material.


3. Index the torch from pierce height to cut height, which must be done before the torch reaches the radius contour of the hole. The long lead-in also allows the torch air pressure to stabilize.

• The lead-in design is based on your machines acceleration capability and mechanical tightness. Machines with low acceleration rates and mechanical backlash tend to make better holes with a radial lead-in shape. Tight machines with excellent acceleration (in the .3G range) will make better holes with a straight lead-in. Starting near the center with the lead-in also allows the slag pile, the pile of metal on top of the plate around the pierce hole, from interfering with the arc during the hole contour. If the arc passes over top slag during cutting, it will deflect. This deflection is usually noticed in the form of a “divot” inside the hole shape.


• Best practice for holes under 1-1/4” diameter is to program the speed at approximately 60 percent of the suggested best quality speed for the material being cut. Again, if you look at your owner’s manual, you’ll see the suggested best speed on 5/8” steel when cutting at 65 amps is 23 inches per minute. So in this case, you’ll want to program all holes under 1-1/4” to cut at about 14 inches per minute. Though this lower speed will produce a little dross on the bottom, it will reduce the amount of taper in the hole.


• Finally, design your hole program to use an overburn at the end of the hole. Do not use a lead-out into the center slug as this will create an anomaly in the shape of the hole and shorten the plasma consumable parts life. An overburn is simply staying on the hole radius past the lead-in point by about .150” to .200”. If your CNC control and CAM software have the ability, it is actually best to extinguish the plasma right at the 360 degree lead-in kerf crossing, yet continue the motion on the hole radius for the .150” to .200” distance. The plasma arc takes a few milliseconds to fully extinguish, and this technique, if possible on your system, will smooth out the transition between the lead-in and the end of the cut.

Jim Colt