B/S sizing was Re: Ball screws

Darrell,

Some reasons you see rack/pinion drive on plasma cnc is:

1)plasma cutting is relatively inaccurate, so the ballscrew is
overkill.
2)plasma cutting goes through the part, so a twin screw is needed (or
lots of structure), increasing cost.
3)It is working well on many machines. (proven technique)
3)ballscrews are very INtolerant of dust/debris. Plasma cutters are
notorious FOR dust/debris.
4)higher speeds are attained more easily with rack/pinion than
ballscrew(s), and at lower cost.
5)low cutting forces do not require the mechanical efficiency of
ballscrews.

As to your "what size" question: You haven't provided enough
information to give a definite answer, but I CAN say that a 5/8
ballscrew can be made to work well in this size. And is very commonly
used. The end mounts and other details will need to be selected based
on additional info.

The 5/8 and 1 inch size of ballscrews are generally much less
expensive than other sizes, due to supply/demand.

That said, If I were you, based on what you have told us so far; I'd
use rack/pinion drive.

Hope this helps.

Ballendo

--- In CAD_CAM_EDM_DRO@y..., Darrell Daniels <ddaniel1@s...> wrote:
> This brings up a question I have, with 36" between supports on both
the
> X and Y axis, both ends supported, supports will be extruded
aluminum
> channels, what size ballscews should I look at? This is for a plasma
> cutter gantry I am designing, I have noticed most commercial
designs go
> with direct gears and tracks. What will be the trade off in speed
> between the ballscrew idea and a direct gear method? Speed will be a
> major concern with thinner metals being cut. I dont have the weight
of
> the cutting head yet but it will be fairly light, this is the rough
> design stage. Searching the archive...
> Darrell