9 Common CNC Plasma Cutting Mistakes & How to Avoid Them

Whether you’re new to the CNC plasma cutting business or are an experienced professional, slip-ups can occur in the workshop. Mistakes result in the wastage of expensive materials, loss of valuable time and money, and significantly angry customers.

However, these mistakes can be avoided, and these losses can be reduced by implementing the best CNC plasma machine cutting practices that will help enhance efficiency, improve output and quality, and, most importantly, increase customer base and profitability.

How to Avoid Common CNC Plasma Cutting Mistakes


Source: How Stuff Works

Mistakes mainly occur due to the consumable lifespan or computer numerical control (CNC) that causes poor plasma-cut quality. Rectifying these factors and efficiently using a well-maintained CNC plasma machine will help save your business time, money, and resources and generate consistent revenue.

Here are nine common mistakes that can occur in your workplace and how you can avoid them.

1.    Using Consumables Beyond their Average Lifespan

Using consumables beyond their lifespan is known in the workplace as using consumables ‘until they blow.’ Every consumable has an average lifespan that varies depending on the cutting technique and the material being cut. Using extensively worn-out consumables ruins the metal and results in expensive torch failures and pointless downtime.

To avoid this mistake, record how long each consumable lasts by either using the number of starts or the arc-on time. In addition, routinely examine the cut-edge of your workpiece and check the torch parts for a decline in quality. Henceforth, you can develop guidelines for average life spans based on materials, amperage, cut thickness, and smartly plan consumable replacements.

2.    Replacing Consumables Too Soon

While some operators use consumables until they blow, others discard them too soon. To avoid this, don’t focus on how many hours they’ve been used; instead, check how much they’ve worn. For example, examine gouges inside or outside the nozzle, the roundness of the orifice, etc. If such factors check out, then your consumables can still be used.

Some other tips to avoid this mistake include the following:

  • To tell if an electrode is worn, examine the hafnium pit in the center and replace it if it is too low.
  • Replace gas swirl rings if a detailed examination exposes grease or dirt in the holes in addition to arc burns and cracks.
  • Shields should be replaced if they are physically damaged; otherwise, they can be cleaned and reused.

3.    Using the Wrong Consumables/Parameters

Consumable selection is based mainly on the material and thickness of the cut, the amperage, the plasma gas used, and other arc-cutting parameters. Using the wrong consumables can shorten the life of your machine’s parts and significantly lower cut quality. Similarly, running parts at the correct amperage is crucial; very low amperage results in a messy cut, whereas a very high amperage can damage the nozzle.

Consult your CNC plasma machine's operator's manual to ensure you use the correct consumables and parameters.

4.    Assembling the Torch Uncleanly and Incorrectly 

Perfect torch assembly is mandatory for efficient operations and satisfactory output. Before beginning operations, ensure all parts of your CNC plasma machine are precisely aligned and fit snugly. No part should be askew or forced to fit into another. Moreover, cleanliness is vital in plasma torch assembly since it ensures efficient electrical contact between all the parts.

While assembling your torch, clean any dust or oil on the parts with a clean rag. Furthermore, don’t lubricate the parts excessively; just use enough to create a shine on the O-ring. Unnecessary lubrication can lead to clogging and metal dust contamination inside the torch, resulting in uncontrolled arcing in the plasma chamber and potential torch failure. Also, never use grease for lubrication since this will cause destructive arcing and burning inside the torch.

5.    Inappropriate Gas or Coolant Flow/Pressure

Compressed air systems like those in a CNC plasma machine are extremely susceptible to moisture, oil, and particulate contamination. Hence, if a continuous and appropriate flow of gas is not maintained, the life of consumables will decline. Similarly, the inadequate flow of cooling water because of clogged filters, worn-out pumps, low coolant levels, etc., can result in system failure.

Additionally, consistent gas pressure is vital for maintaining the cutting arc. Excessive pressure results in ‘hard starting’ where the torch does not initiate an angle despite all other correct conditions for routine operations. Extreme gas pressure also leads to the quick corrosion of electrodes.

To avoid having problems with gas and coolant flow/pressure, make sure that you check these parameters at least once a day.

6.    Inappropriate Cutting Speed

Cutting too fast or too slow uses consumables faster than normal and adversely affects the quality of your cut. If your plasma machine cuts too slow, you’ll get a substantial bubbly accumulation called ‘dross’ along the bottom edge of your product. Moreover, it will lead to a wider kerf and additional top spatter. Similarly, cutting too fast will result in a lag back in the kerf and a small, hard bead of uncut material (rollover dross) along the bottom of your product.

Use the appropriate speed and consumables for the cut material to attain the best-cut quality.


Source: Westermans 

7.    Inadequate Piercing Height

All good operators know that the distance between the fabricated material and the torch tip drastically affects cut quality. However, a common mistake operators make is piercing very low. This leads to the molten metal spattering all over the front of the shield and nozzle and shield. Moreover, suppose the torch pierces while touching the metal or drags over the surface during cutting. In that case, something known as ‘arc snuffing’ can occur, resulting in your consumable parts, and occasionally your torch, being destroyed.

This dramatic mistake can be avoided by utilizing an Automatic Torch Height Control (ATHC) to identify the correct piercing height. This is usually included in your CNC plasma machine’s automation system.

8.    Stretching the Arc

Arc stretching can occur at the start or the end of the cut. This happens when the arc is not centered and has to stretch to some extent to reach the workpiece, resulting in the angle cutting into and damaging the side wall of your CNC plasma machine’s nozzle.

To ensure this mistake doesn’t happen, always check and confirm that your CNC cutter’s arc is centered directly over the workpiece before beginning the operation.

9.    Overlooking Routine Maintenance

And possibly the most common mistake while using a CNC plasma machine is overlooking routine maintenance. You might have the best CNC cutter in the market and the most experienced professionals using it. Yet, your output and efficiency will be significantly affected without proper maintenance and cleaning.

Here are a few essential factors you must monitor to ensure the longevity of your CNC plasma machine:

  • Make sure to check your consumables regularly for wear and tear
  • Clean the torch threads regularly; with proper care, they can last for years
  • Examine seating areas for mechanical damage and contamination
  • Clean any dirt, dust, or excess lubricant using a cotton swab, electrical contact cleaner, or hydrogen peroxide.

Final Thoughts

Using a CNC plasma cutter requires precision, focus, and knowledge about the metal fabrication craft. However, to err is human, and even experienced individuals can make mistakes.

However, knowing how to avoid these mistakes can save you from disrupting your production processes and save you countless dollars. Moreover, it is important that everyone in your workforce is familiar with the tips we’ve listed and knows what to do in case of a slip-up.