Basic plasma cutters use electricity to superheat air into plasma (the 4th state of matter), which is then blown through the metal to be cut. Plasma cutters require a compressed air supply and AC power to operate.
1. Initially, the electrode is in contact with (touches) the nozzle.
2. When the trigger is squeezed, DC current flows through this contact.
3. Next, compressed air starts moving the electrode back and flows out the nozzle.
4. A fixed gap is established between the electrode and the nozzle. (The power supply increases voltage in order to maintain a constant current through the joint.) Electrons arc though the gap, turning the air into plasma.
5. Finally, the regulated DC current is switched so that it no longer flows to the nozzle but instead flows from the electrode to the work piece. Current and airflow continue until cutting is halted.
• The nozzle and electrode require periodic replacement. For this reason, they are called “consumables.” Plasma cutters are only useful for cutting metal. Non-conductive materials like wood and plastic prevent the plasma cutter from doing step 5 above.
• The above steps describe the operation of a contact start plasma torch. Some older plasma torch designs use high voltage sparks to bridge the gap between a fixed electrode and nozzle when starting the arc. These high frequency/high voltage start units are generally not recommended for use with a computerized machine, because they cause severe electromagnetic interference.
Why do Technocrats make CNC Profile cutting machines use servo motors instead of stepper motors?
It's true that this machine could be made a lot cheaper if we use stepper motors and drives instead of high-tech servo motor systems. But when it comes to something this critical, quality cannot be compromised. Experienced machine tool users know that servo motors are vastly superior to stepper motors, because newer, high-performance machines (like CNC mills) use servo motors, whereas older, more troublesome machines used stepper motors. Yet the real reason for the performance difference requires some explanation.
The servo motors we use, use optically-encoded feedback, so the controlling software always knows the true position of the machine. A simple stepper motor controller must “trust” that the motor has moved exactly as requested each time a step current is made. Without feedback, the controller cannot identify and correct whenever the motor misses a few steps (like during jolts, vibrations, hang-ups, etc). Since a single shape may require millions of steps to trace, errors in position will continue to accumulate unbeknownst to the controller, until the machine is finally re-zeroed against a physical stop. Hence, errors in stepper position are both unpredictable and unreported.
To solve this problem, optical encoders can be coupled to stepper motors so the controller can determine the true position and make corrections when needed. However, the added cost and complexity prevents the system from being a low-budget alternative to servo systems. The more common solution involves overrating the motors (using larger, higher-geared motors that are under-utilized) to reduce the probability of slipping. This extra rotating inertia (typically much greater than the mass of the moving parts) brings undesirable side effects: diminished acceleration and speed. For plasma cutting, the machine's ability to cut intricate shapes (which require abrupt changes in direction during high-speed cutting) would be greatly limited.
Powerful, lightweight motors are a must, because their torque is needed for speeding up and slowing down all the moving mass – including the spinning motor armatures. (To picture the importance of this, imagine pushing a 100 lb cart at a walking pace and trying to make a sharp 90 degree turn without overshooting at all.) That's why these Servo motors fully utilize the 300 oz-in capability, providing over 1.5 G of acceleration. (An object traveling at 100 inches per minute can totally reverse direction in only 0.002 inch at this acceleration.) See the photos of intricate sample parts throughout this web site and watch the demo video to see what this machine can do for you.
Why do Technocrats make CNC Profile cutting machines use steel frame components instead of aluminum?
Our machines are made from cold-rolled steel components. Steel is much more durable and has a higher melting point than aluminum. Our precision manufacturing process allows higher accuracy as well. Comparing tolerances, our guide rails are about 3 times straighter than standard aluminum extrusions.
Another benefit of an all-steel frame is that temperature distortion is avoided. If we used aluminum frame pieces, we would still have to bolt steel parts to them (like gear racks and guides). This would create bi-metal strips that actually curve under temperature changes. Also, the whole table would grow and shrink under the material. But since all steel is used, the machine remains accurate to the material.