How to get clean straight or circle cuts

When it comes to plasma cutting, a lot of things can affect the final cut quality — amperage, torch height, cutting speed, and even the state of your consumables. We’ve already covered these topics in more detail in our earlier posts, Enhancing your plasma cutting qualityor Reading the cut. This time, we’ll focus on the essential pre-cutting checks and walk you through a practical cutting demonstration to help you achieve cleaner, more consistent results right from the start. What cutting technique should you choose to achieve the best results? We will advise you in the following paragraphs.

Prior to start cutting, visually check power cable and work leads for damage. After that check also torch body, connector pins, leads and safety trigger cap. As a third step it is important to choose the right set of consumables and if already used for possible damage, or wear before another use. All the steps are clearly shown in the video below. Do not forget to connect work leads to the material to be cut. Once the installation is complete, you can start cutting.

Video: Cutting system installation and first run.
This is an illustrative video only. The torch design shown in the video is from the 1st generation and has been upgraded. The single steps remain the same.

Hand torch cutting technique

Avoid unnecessary firing of the torch, each firing of the torch reduces the lifetime of the electrode and nozzle.

When cutting, ensure the arc spray exits the underside of the workpiece. Incomplete severance is indicated by an upward arc spray. This can be caused by the following: excessive travel speed, incorrect power settings or gas pressure settings, or bad condition of consumables. Hold the torch vertically and watch the arc while cutting along the line.

Always use shielded consumables.

Make light contact between the shield and the workpiece, pull the torch at a steady travel speed.

• For straight line/bevel cutting, use a straight edge as a guide.
• Pulling the torch gives better control compared to pushing.
• For cutting thin material, reduce the amperage to the optimum to achieve the highest cut quality.

The appearance of dross is relevant to the cutting speed. Using the correct cutting speed can deliver a dross free cut. The proper set up of operation data for a given material thickness is noted in the mid-range of cut chart.

Picture: Hand plasma cutting torch FHT-EX^® 105RTXH

Straight cutting – cut direction

The compressed air in the torch swirls around the electrode inside the plasma chamber helping the plasma arc constriction and part of the reason for that is to get a straight cut. However, you really get a straight cut more on one side of the arc than on the other. On the most plasma cutting machines it is on the right size, so check rather twice the cut direction the torch is going.

Picture: Choosing the right cut direction

Circle cutting technique

• First, prepare the table for cutting (the table differs from the classic workshop table). Place the template and draw the openings onto the metal sheet. You can also use the circle cutting guide kit to achieve perfectly round circles. Secure the template with clamps.
• Set the power supply to the appropriate cutting parameters according to the material type and thickness to be cut – more information you can find in the operation manual.
• For a repeatable circle cutting we recommend using some metal template or use a circle cutting guide kit, which makes work easier.

Video: Cutting circles with the EX-TRAFIRE^® 30H plasma cutting system

Picture: Hand plasma cutting with circle cutting guide kit

Plasma tip: Orifice size vs amperage

“You should increase the cutting current in line with the thickness of the material you are cutting. The same applies to the appropriate consumables that correspond with the cutting current. The set of nozzle, swirl ring and electrode is especially important.”

Final recommendations

• Cutting issues? Prior to making any alterations, check the condition of the consumables, check the part numbers are correct and the cutting variables match the manufacturers recommended settings.
• Small adjustments to the cut charts settings may be needed to compensate for a change in material quality, material temperature or a specific material type.
• Make small incremental changes when adjusting settings.
• Using the recommended cut chart values for cutting speed and arc voltage maximises cutting performance.
• The cut chart variables are interdependent, changing one setting affects all others and may influence the overall cut quality.

Plasma cutting system: EX-TRAFIRE® 55SD up to 55 A

The EX-TRAFIRE® 55SD three-phase plasma cutter, which we are presenting here, is a handheld cutting system with the FHT-EX® 105RTX torch, which is available in lengths of 8 or 15 metres. It also features an ergonomic torch handle which reduces fatigue during long-term use. The system is compact and highly flexible for cutting in hard-to-reach places. It is particularly suitable for cutting sheet metal up to a thickness of 30 mm while providing sufficient power reserve.

Consumables used

We hope the article was useful for you. We also recommend another article related to the theme, Enhancing your plasma cutting quality. If you needed any further help, please do not hesitate to contact us at the following email: support@thermacut.cz

Text:      Thermacut, k. s.,
Photo:   archive of Thermacut, k. s.