Re: plasma setup-leadscrew vs. rack & pinion + software

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Les Newell" <les@l...> wrote:

> Plasma cutting is not a very accurate process so don't waste your

money on

> ballscrews or acme leadscrews. They will be too low geared and will

fill up <snip>


I just finished up a similar table. It is designed to be both a
plasma and a router table so compromises had to be made. Router
tables need accuracy and torque while plasma tables need speed.

I used ballscrews because I got them cheap. The ballscrews (5TPI)
limit the speed to about 180IPM because of "whipping". When you spin
long lengths of screw rod rapidly, it tends to start warping (bowing)
and can cause rapid wear in bearings and other components.

If I was going to build just a plasma table I would probably pick
rack and pinion. To figure what size gears you need, decided what
the fastest speed is you want your rapid moves to be and work back
using the step speed of the motors. It's always a tradeoff of speed
vs torque but on a plasma setup there is no drag created from the
cutter (hopefully) so the torque needs are low. There are standard
off-the-shelf rack and pinion sets so refine your design to fit
what's available and cheap.

For the Controller Software I have settled on MACH1 from the same guy
that wrote Master5 (mentioned by another list member). I chose it
for several reasons but they primary one is that it is constantly
being improved. One of the promised improvements is to incorporate
the logic for doing a really low cost Torch Height Control (THC) by
measuring the cut voltage and adjusting the Z height. Be advised that
MACH1 needs WIN2000 or XP to run. Check out the Master5 Group on
yahoo.

It won't help you now, but servo motors tend to have better RPM specs
and better torque at high speeds. Getting 1500 or even 3000 rpm out
of a servo motor is easy. Your gearing will have to be higher for
steppers to get the same IPM moves. Take a look at www.plasmacam.com
for some ideas about rack and pinion setups.

Drop me a line off list and I can go into detail about the THC plans
and some ideas for torch holders.