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

Hello,

Roller chain (#25, or even bicycle chain) can work really well for
plasma. Fix the chain at both ends, and move the motor/sprocket. An
idler sprocket or two adds "wrap" to the motor sprocket. If your
motors are small, try a 4:1 reduction before the final output. BTW,
this will work for routers too...

Hope this helps,

Ballendo

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "caudlet <info@t...>"
<info@t...> wrote:

> --- 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.