The Fabricator - Sample Issue

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Using the Right Consumables

Tips focus the plasma stream to the workpiece. Some plasma cutters use separate tips for the high and low end of their amperage ranges. For instance, an 80-amp plasma cutter may use 80- amp and 40-amp tips, plus extended versions of those for increased reach, as well as gouging tips.

The higher-amp tip is used when the plasma cutter is set to its upper amperage ranges for cutting thick material. As noted previously, to maintain a thin kerf when cutting sheet metal, set the machine to a lower-range amperage and use a low-amp tip. Because a low-amp tip has a smaller orifice, it maintains a narrow plasma stream at lower settings for use on thin-gauge material. Using a 40- amp tip at an 80-amp setting will distort the tip orifice and require replacement. Conversely, using an 80-amp tip on the lower settings will not allow you to focus the plasma stream as well and creates a wide kerf.

Use extended tips to cut patterns or to reach into corners or tight areas.

Use gouging tips to spread the plasma stream and the arc so you can remove a large amount of material all at once in a single pass.

If you are using clean, dry air and making long cuts, you can expect your consumables to last for approximately two hours of continuous cutting time. Continuously restarting the pilot arc by triggering the torch shortens consumable life. Touching the tip to the material without a drag shield in place causes double arcing, because the electrical current tries to find the shortest path to the workpiece. This decreases consumable life too.

Best Techniques

If you’re not using a drag shield, or are trying to make very precise cuts, place your noncutting hand down (see Figure 5) and use it as a guide for the other hand. This rest hand position allows freedom of movement in all directions while helping you steady your hand and maintain a constant standoff.

Keep the torch perpendicular to the workpiece whenever possible, except when you are beveling.

When you are piercing thin material to start a cut, you may be able to punch through it with little or no arc backsplash. However, on thick material, start with the torch on a 45- degree angle so the first blast of metal has somewhere to go. If not, the metal will splash back and quickly wear your consumables.

As noted, at the optimal travel speed, the arc will exit the material at a 15- to 20-degree angle opposite the direction of travel. Therefore, the cut also will be at an angle opposite the direction of travel. At the end of a cut, angle the torch forward to cleanly cut the last bit of metal (see Figure 6).

Guides. To mark the material to be cut, use either a black marker or white chalk. Contrast makes the marks easier to see.

For more precise cutting, you may clamp a straight edge to the workpiece to guide the torch (see Figure 7). If you’ll be making multiple cuts of the same shape, create a template.

Make sure the guide isn’t flammable. Aluminum is preferable because of its smooth surface, but because of its electrical conductivity, the aluminum should touch the torch cup or drag shield and not contact the tip.

Circle guides also are available to help ensure precise cutting (see Figure 8). A center punch is used in preparation for using a circle-cutting guide. An easy way to make a bevel cut is to use a piece of angle iron as your guide (see Figure 9).

While it may be easy enough to unpack your plasma cutter and begin cutting, take the time to familiarize yourself with its proper operation. It bears repeating that you should read the owner’s manual first. ■

Don Keddell is the plasma training manager for Miller Electric Manufacturing Co., 1635 W. Spencer St., Appleton, WI 54912-1079, 920-734-9821, www.millerwelds.com.