On 04/04/2013 02:54 AM, Gregg Eshelman wrote:
> Anyone using LinuxCNC with a CandCNC Dragon Cut system? That hardware
> looks like the perfect setup for a large plasma table, provided I can
> keep the gantry weight down. Would definitely save a lot of time
> making bits and pieces from various sources work together.
>
> I still want to make a few pennies scream by using free software
> instead of Mach3. ;-)
>
> What bugs me about it, and many other kits for plasma tables, is the
> motor for the Z axis is wy overpowered. 620 oz-in for moving
> the gantry, but for raising and lowering a torch head that only
> weighs a few pounds?
>
> The only other motor option they show is all motors at 300 oz-in.
> That's still using a sledgehammer to crack eggs for the Z axis.
>
> Now if I could come up with a way to use all that excess power,
> perhaps a second head fitting with a drill chuck and its own spindle
> motor, use the 620 oz-in grunt to push it down.
Don't be so sure it's excess power! The biggest thing is that you need
to be able to accelerate the Z quickly for direction changes. The
faster the X/Y axes move, the faster the Z has to accelerate. In order
to get the best cut on thinner metal (which is mainly where you need a
THC), you have to move the gantry quite fast, and so the Z has to be
able to keep up. For instance, the Hypertherm manual calls for a rate
of 350 in/min in 16 guage mild steel with a 45A shielded tip for best
quality, and 400 in/min for production.
I have seen tables that were able to move at the speeds required for the
material thickness, but the Z limited it so the whole thing had to be
slowed down.
Moses
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