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Basic Tips to Improve Plasma Cutting Performance

When it comes to plasma cutting for home hobby, motorsports, art and DIY projects, using the right techniques will make the job easier and improve results. The first part of this article and associated video dives right into the basic mechanics of good plasma cutting. The second portion of the article and part 2 of the video provides guidelines for plasma cutting safety, proper equipment set up and shows you some cool accessories that make cutting easier.

Obligatory safety warning: It is your responsibility to thoroughly read your owner's manual to familiarize yourself with the safe and correct operation of your particular plasma cutter.

 Part 1: Cutting Techniques & Tips

1.     Before you even think about pulling the trigger, brace yourself. Use your non-cutting hand as a support for your other hand (see Fig. 1). This steadies your cutting hand, provides freedom of movement in all directions and helps maintain a constant 1/16th - 1/8th inch standoff (Fig. 2; more on standoff in the next section). Note that most people find it easier to pull a torch toward their body rather than push it away.

 


Fig. 1—Support your cutting hand with non-cutting hand for greater stability. 

 

 

Fig. 2-Holding a stand of 1/16th to 1/8th of an inch increases cutting performance.

2.     Again without pulling the trigger, trace the path you plan to cut. On long cuts, practice your movements before pulling the trigger to make sure you have adequate freedom of movement to make one continuous cut. Stopping and starting again in the same spot is hard and typically creates irregularities in the cut edge.

3.     To ensure you're using the right amperage settings and travel speed, make a sample cut on the same type of material you actually plan to cut.

4.     If sparks shoot along the top of the material, it means you're moving too fast. With a proper travel speed, the arc should exit the material at a 15- to 20-degree angle opposite the direction of travel (you can actually see this angle in the cut metal, Fig. 3).

 

 

Fig. 3-Proper travel speed creates 15- to 20-degree "drag lines"
opposite the direction of travel (which was right to left in this case). 

5.     On thicker material, severing the last little piece can be tricky. To make a clean cut, roll the torch tip slightly towards the final edge or pause briefly to completely sever the metal at the end of the cut.

6.     Cutting thick metal at your machine's maximum output leaves dross on the bottom of the cut (Fig. 4), but don't worry. It can be removed easily with a chipping hammer or other piece of metal.

 

 

Fig. 4-The dross produced by plasma cutting, shown here
in its orange-hot molten stage, easily comes off with a chipping hammer.

7.     For piercing thin metal, simply place the torch on the workpiece and pull the trigger; the force of the arc will punch right through. For thicker metal, you want to avoid a backsplash of molten metal, as this quickly degrades consumables life. To pierce thick metal, angle the torch about 45 degrees (in a direction away from your body!), initiate the arc and roll the torch into a vertical position.

8.     Plasma works great for cutting bolt holes and works faster than a drill. Simply pierce the metal, and then trace a small circle. Note that a machine can pierce metal up to one-half of its cutting thickness.

9.     To bevel an edge, which can help with fit-up or obtaining 100% penetration on thicker material, simply tilt the torch at a 30- to 40-degree angle and make your cut (Fig. 5).

 

 

Fig. 5-Bevel an edge simply by angling your torch when cutting.

Part 2: Set-Up, Safety & Tips for Accuracy

1.     Before cutting, please thoroughly read your owner's manual regarding safety precautions.

2.     Proper plasma safety, like welding safety, requires protecting exposed skin (Fig. 6). You'll need welding gloves and a welding jacket or other flame-resistant clothing (denim is actually a pretty good choice). Button your shirt cuffs, pockets and collar so they don't catch sparks.

 

 

Fig. 6-Plasma safety gear includes a gloves, glasses
or helmet with a #3 - #6 shade and regular safety glasses
to wear when not cutting.

3.     Shield your eyes with the proper shade lens for the plasma cutter you plan to use. Miller owner's manuals state that a #3 to #6 shade can be used for cutting at 60 amps or lower (which covers the Spectrum 375 X-TREME up to the Spectrum 875).You can use traditional plasma cutting/oxy-fuel goggles or a welding helmet with a "cutting mode" (cutting mode offers a #3 to #5 shade; the #8 to #13 shades used for welding may be too dark for plasma cutting).

4.     Use ordinary compressed air as the cutting gas. Note that in mobile applications, contractors often opt for bottled nitrogen because it may cost less than bottled air. When cutting stainless steel, some people believe nitrogen produces slightly less oxidation, but it's not significantly different than air.

5.     If oil or water contaminates your air supply, they will quickly reduce the life of the consumables. Miller offers an in-line air filter (Fig. 7) that removes 99.9% of oil and water. Since a tip and electrode together cost about $12, air filters make for a smart investment.

 

 

Fig. 7-Miller's in-line air filter removes 99.9% of contaminants
and features an easily replaceable filter.

6.     Worn consumables (Fig. 8) will cause cutting inaccuracies and/or arc starting problems, so inspect your consumables regularly. When the tip hole becomes irregular and/or covered with spatter, discard it. The electrode (the part right underneath the tip) contains a small amount of highly conductive material called hafnium. Each arc start consumes a small amount of hafnium. When the tip of the electrode develops a pit, discard it.

 

 

Fig. 8-New consumables (at left) provide positive arc initiation
and smoother cuts. Replace electrodes when they become
pitted (top right) and tips (bottom right) when the hole becomes worn.

7.     Don't over-tighten the consumables retaining cup. The parts inside actually need to move (become separated) to create an arc, so only finger tighten the cup.

8.     Secure the ground clamp to clean metal only (Fig. 9). If necessary, grind off rust or paint, as they inhibit the flow of electricity.

 

 

Fig. 9-Clamping to clean metal provides the best cutting
performance, so grind off any paint or rust before clamping. 

9.     Place the ground clamp as close to the cut as possible, or place the clamp on the work piece itself if possible. Check your cables for worn spots, loose connections or anything that could add unnecessary resistance to electrical flow.

10.  Generally speaking, you can turn your plasma cutter's output to maximum, leave it there and make any adjustments by changing your travel speed. However, if you plug the unit into a smaller-than-recommend circuit, you will need to reduce output to avoid tripping the breaker. Miller recommends a 30-amp circuit breaker when using its Spectrum® 375 and 625 X-TREMETM models.

11.  Holding a 1/16 - 1/8 inch standoff increases the cutting capacity of smaller machines, and it extends the consumables life. Use a drag shield if your plasma cutter is equipped with one. A drag shield allows you to rest the torch on the workpiece while maintaining an optimal standoff without touching the tip to the metal (Fig. 10), which will adversely affect your cut quality and consumable life.

 

Fig. 10—This close-up of a drag shield shows how it
automatically creates a proper standoff for the torch tip.

12.  Another easy way to maintain a consistent standoff is to use a roller guide (Fig. 11). The roller guide also makes cutting straight lines really easy: just clamp a straight edge, piece of metal or other guide to your work piece and follow the edge.

 

Fig. 11—Roller guides make it very easy to follow a
straight edge, as well as hold a proper standoff.

13.  Circle guides (which also hold a standoff) allow you to cut perfect circles of vary ing sizes every time (Fig. 12).

 

Fig. 12—Use circle guides for cutting perfect circles every time.

14.  For cutting specific and/or repeatable shapes, make a template and trace along the edge. Remember to consider the cut width when determining template size! When possible, clamp the template to the base metal so it doesn't shift during cutting (Fig. 13).

 

Fig. 13—Clamp templates in place so they don’t move during cutting.

When using your plasma cutter, keep the preceding tips in mind. It will help you optimize your plasma cutting for better fit-up, increased productivity and lower operating costs. Visit MillerWelds.com/resources/improving-your-skills/plasma/ for more plasma cutting resources, including videos and how-to articles. 

 

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Watch the video Plasma Cutting Techniques, Part 1.


Watch the video Plasma Cutting Techniques, Part 2.

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