[TheForge] Re:3 axis plasma cutting

[Ries Niemi]

My plasma table, which is not cnc, but optical trace, has 3 axis 
motors, and I wouldnt think of having one without it. The third, z 
axis, is controlled by  a voltage sensing circuit that samples the 
voltage from the plasma power supply. It then adjusts the height 
accordingly, so the arc gap is always consistent. This means the torch 
is always cutting at its most efficient, but more importantly it will 
follow the warped surface of a piece of plate. Even though I built my 
water table flat, then levelled it in the shop, not every piece of 
sheet metal is flat. And then, when you start cutting it, it warps like 
crazy. Especially thinner stuff like 16ga- It can warp an inch or more 
in height as you cut parts out. If the plasma cutter doesnt have z axis 
adjustment, the torch either runs into the metal, and you lose 
registration, or it gets so high you lose contact and the torch goes 
out. Either way, bad news. So 3 axis is needed unless you want to 
manually adjust the torch height every inch of the way.
Personally I prefer my optical trace table to a full on cnc one. I can 
do a full size drawing of the part up to 4' x 8', and it goes on the 
right side of the machine, then I lay a 4x8 sheet of metal on the water 
table on the left. It is a little slower than full cnc when you are 
cutting more than 20 or 30 parts, but I dont do that kind of quantity 
anyway very often. More often I will be cutting a full sheet in a very 
complicated pattern, once. I just finished a job where we had to make a 
4 foot by 16 foot artwork panel out of 3/16" plate, and to troubleshoot 
the design in software on the computer would have taken twice as long 
as cutting it would have. Plus, I am an artist, and it is easy enough 
for me to draw what I want.

ries