re:Cnc router help

Wilfrid,

I think you are going to have problems with a 3/4 ballscrew eight
feet long... I would spin the ballnut and mount the ballscrew in
tension (slightly) This eliminates the need to machine the ends of
the long screw, and will greatly reduce resonance and shaft
compression load factors (you will need a solid structure to attach
the ends to, as you are trying to create a 'tension' load instead of
a compression load.)

The 3/4 by five foot might be okay with good endmounts. Here I'd
suggest at least one RIGID style end mount, maybe both. Depends on
the speed you're hoping to achieve.

As Les said, be sure to use the mfr tables for ballscrew selection!
They know what they're doing!

Lastly, did I understand you are going to have a 3 foot Z axis!!? Be
careful here! The moment loads (especially on a gantry style machine)
add up quickly! Most people don't REALLY NEED the "large Z axis
travel they think they do... Especially since it often costs so much
in machine stiffness, which is felt at ALL positions...
I suggest the shortest Z you can "get away with", and a move-able
bridge or table structure...

Hope this helps.

Ballendo

>As for the lengths- 66 and particularly 96x.75 ballscrews will
>have very low critical speeds and safe compression loads.

<s>Please review the thomson design tables in the catalog or on line

>at their web site.