Thc disable

Use mild steel, slats 5cm high for up to 100A, 2mm thick slats are good even 1.5 is OK if they are arced.
Go buy 1KG of baking soda and throw it on the table after filling with water, it does not let the metal rust as long as there is water in it. Add food coloring if you want to make it look "cool".

paulsao wrote:

..... any advice or suggestion to improve?

Yes, do not cut small holes!
Plasma can not cut such small holes as you are expecting it, the air that does the cutting is spinning fast while cutting so changes in direction will change the cut angle.
Anything under 30mm on 3 to 5mm thick material will not be perfectly round, 20mm hole will have nearly 1mm difference on 5mm material, etc etc.
Search for "true hole technology" from hypertherm just to get an idea on what it takes to do good holes, even that might not do 8mm perfectly.
Having said that, try slower feed rate, that always helps on holes, use small nozzles and low power so the machine can have some time to remove material.

BTW, do not try to drill holes done with plasma, especially if using water table, the surface of the cut will be much harder than the drill.
Carbide drills do work, but the price is ....

Yeah, i did the same, went through 3 new Bosch drill bits till it occurred to me what is going on!