Hi,
the issue is lets say you want to cut from 0,0 the current location to 150,150 (in mm) through 6mm steel.
Lets ay you also know that you can cut at 1000m/min with 6mm steel. You could cause this to happen by coding:
G1 X150 Y150 F 1000.
The machine cannot go from zero speed to 1000mm/min instantly, it will have to accelerate up to speed. Likewise at the end of the cut the machine
will have to decelerate to a stop. During the acceleration and deceleration the plasma arc voltage will vary. It might be stable at 100V during the majority of the cut
but the 10mm at each end the voltage will increase, and that is where you expect the tip of the torch to go down a little bit to maintain the right, or optimum cutting voltage.
But what happens when it actually stops, the voltage will increase and the THC will try to drive the tip into the material. This is called 'tip dive'. A good THC system
will have strategies to overcome this called 'anti dive'. It will include at look ahead through the Gcode to find places where it might expect the tip to dive and counter it.
I suspect this is where your notion to use an Arduino will fall short. Very simple THC systems often have the problem of tip dive, and they don't accommodate it well.
Another sure-fire test for a THC system is if you go and do a cross cut over the top of a previous cut. Right at the moment that the arc is in the other cut the voltage will spike high
and the tip of the torch will dive into the plate. For this reason its considered poor practice to cut over the top of an existing cut with simple THC. A good THC with good anti-dive
strategies can do it whereas simple ones fail.
Craig