Pierce height and pierce delay time is often overlooked, many operators are happy if the arc pierces the material and the cut begins successfully. The truth is that you can reduce frustration, reduce your cutting costs, and increase productivity by paying closer attention to your pierce settings, and it's really not difficult at all.
Piercing material is hard on the nozzle, much harder than just cutting, and the thicker the material is, the harder it will be on the nozzle. This is because thicker material takes longer to pierce, and because more molten metal will be ejected upwards toward your torch prior to blowing a hole through the bottom. Shops that cut a lot of thick plate will often use chain cutting, or edge starts to eliminate the number of pierces, but with metal art you typically can't escape high pierce counts.
We have established that even a perfect pierce will be hard on the nozzle, but an imperfect pierce could destroy a brand-new nozzle before you even cut 1 inch of material. This is a common source of frustration for many new operators. The most common mistake when piercing is being too close to the material or in contact with the material. You can't trust that you are at the correct pierce height just because you have the proper height set in your software, you must stop and measure your pierce height to be sure it is correct. The best way to measure pierce height is to run your program and pause the machine after the initial height sensing is complete, and the torch has raised to the pierce height set in your software. Use a set of feeler gauges to determine what the height is. The correct height can be found in the cut charts for your plasma cutter, or a good rule of thumb is 1.5-2 times the cut height.
If your cut height is too low, the most common reason is that the material has flexed down during the initial height sensing and flexed back up when the torch lifted off to the pierce height. The only accurate way to resolve this issue is to hold the material down during the initial height sensing. If material flex is not your issue, it could be that your Z axis is not accurately calibrated, or you could simply have wear and slop in your z axis. Either of these 2 can be resolved by "fudging" the pierce height setting in your software to achieve the correct height. Piercing too high is not as common and can be almost as damaging, but easily corrected by adjusting the pierce height setting in your software.
Once you have your pierce height working perfect, it is time to move on to the pierce delay time, which is typically measured in milliseconds (ms). The correct length of time for the material thickness you are cutting can be found in the cut charts for your plasma cutter, the thicker the material is, the longer it will take to pierce. If cut charts are not available for your plasma cutter, the general rule of thumb is to use the shortest length of time possible. The moment the arc pierces through the material, you want your XY motion to begin. If it is left to pierce for too long, the plasma arc will wander to maintain its transfer to ground, and this will damage your nozzle quickly. If your pierce time is too short, a small section of your part may remain uncut at the beginning.
It is common for operators to disregard things like piercing because it seems so simple and unimportant in the big picture, but it is very important and I hope this helps some operators to improve their performance and consumable life.
Keep cutting and have fun
Important information to prevent common issues faced by many getting started in cnc plasma cutting.
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