Cutting small holes with an air plasma system is a challenging task. It usually requires advanced professional skills and work experience. Deep knowledge of the plasma technology, material characteristics and proper setting of the machine are the key factors for great cutting performance.

One of the most frequently asked questions from our customers at professional training sessions and meetings is how to cut the best small circle holes. In the previous published article “Make your tinsmithing work easier with a small yet powerful plasma cutter” we described cutting small holes with a handheld plasma cutter. This time let´s focus on how to cut small holes with a mechanized air plasma system. For metal sheets with a thickness of minimum of 5mm, we speak of a small hole with a diameter equal to or less than twice the thickness of the metal being cut.

The machine operators often face a challenge to achieve good cut quality. The top of the cut piece is more or less satisfactory, but the hole cross-section tapers towards the bottom side and thus the cut surface is not square.

What are the most important factors affecting the circle cut quality?

1. THC (Torch Height Control) ensuring the automatic control of torch to workpiece distance.

2. The top-quality plasma system with a reliable torch. The plasma system needs to operate with the highest accuracy, no vibration, ensuring smooth torch movement on the CNC gantry cutting machine.

3. Offline programming software supporting the adjustment of cutting parameters suitable for small circle cutting, such as cutting speed setup, auto speed reduction, pierce position, torch height, kerf width, lead in and lead outs.

The system should be able to recognize a small circle and automatically apply adjusted parameters, which is usually the same as the contour cuts, in order to achieve the best results and to avoid possible mistakes. The pierce itself should start on the piercing height in the middle of the circle. Afterwards the THC moves the torch into the correct cutting height, leads in and starts cutting the circle.

The CNC control system should be able to distinguish the material thickness and be able to decrease the cutting speed in comparison with the straight edge cutting speed at a given material thickness. What is also very important is finishing the cut. Try to overburn the trajectory leading into the kerf where the start-cut was, with the torch remaining at the same height. That way the starting point will be less visible. This all is automatically set by the smart software blocking the THC control during the circle cutting operation.

Remember that good cut quality is often the combination and seamless interaction of a high-quality torch, programming software, CNC machine accuracy, condition of the consumables, and THC system.

Complementary information

Check out the video’s series with the correct settings of

EX-TRACK^®CNCto reach the best results.

EX-TRACK^®CNC – basic settings for plasma cutting

EX-TRACK^®CNC – plasma torch position set up

The portable EX-TRACK^®CNC cutting system can operate both plasma and oxy-fuel cutting torches with great results.

Have you already tried the FHT-EX®105RTX torches? The high-quality torches suitable for EX-TRAFIRE®55SD/75SD/100SD plasma cutting systems.

Learn more about whole Thermacut® assortment and visit the official web site www.thermacut.com

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