If for the mechanical part, the plans do not offer much room for interpretation, many questions arise about the choice of control electronics, stepper motors and the electronic power supply. You will find a little theory, explanations and metaphysics on the technical page of PAP engines.
In the following chapters, you will find some more practical tips. However, as usual, use your common sense. Using the best cnc motors is important.
What type of motor control card?
Static, with resistors for current regulation, or with a PWM chopper?
- For motors running slowly without requiring a lot of torque, a single card is sufficient.
- Thus, for hot wire cutting machines, or for a small milling machine for drilling printed circuits or cutting balsa, boards without current regulation, with resistors in series are used.
- If you need speed, and to maintain a certain torque at this speed, you must supply your motors with a high voltage (at least 4 times the nominal voltage of the motor).
- With a card without regulation, this requires large power resistors, which heat up a lot, and the power consumption will be high.
- Also, it is recommended to use a card with PWM regulation, as soon as your speed must exceed 2 revolutions / second, with a minimum torque.
What type of engine?
If you use a PWM based card, you will be able to run fast with your motors. So you can get power, not by having large engine torque, but by settling for medium torque and higher speed, which requires you to increase the reduction ratio.
- Thus, it is possible to use NEMA23 size (57 x 57 mm) motors for large machines, as long as you take good quality motors, with a PWM based control board.
- On the Touchup machine (1.25 mx 2.5 m stroke) are installed two-pole NEMA23 motors developing a torque of 6.2 kg.cm. When you look at the size of the machine, their size looks ridiculous, but it works.
- However, you can salvage old NEMA34 motors (from photocopiers, for example) where the larger size compensates for possibly less advanced technology.
- The weight will be more important, but since these are more powerful engines, that is not a problem.
Automatic plasma cutting bench
The automatic plasma cutting bench is most often associated with a computer. This workshop machine will amaze you with the speed, precision and sharpness of the cuts. And for more efficiency, several torches can be put in battery to multiply the cuts. Investment reserved for factory production.
Working with a plasma cutter implies good visibility of the cutting area which is reduced. As the process generates ultraviolet light, a welding mask is essential. A leather apron and soft gloves complete the protective equipment as well as the gaiters to protect the safety shoes from projections. Note also that nitrogen can replace air, but be careful to ventilate the workstation. Some options are intended to ensure personal safety and facilitate use:
- The thermostatic protection is in the event of overcurrent, over voltage and under voltage, a protection which stops the device in the overheating phase or in the event of an electrical incident.
- The signal of the presence of voltage in the torch gives the starting signal for switching.
- The high frequency HF ignition of the pilot arc allows the cutting to be started at a good distance without the nozzle coming into contact with the metal.