Re: lead screw or rack and pinion ?

Conceptually I like the rotating nut approach also (maybe for the
same reason... <g>), especially for low duty cycle "homebrew"
machines. For me, getting into screws over 1" in dia. gets
expensive, plus it seems like there is a lot of prep work / expense
in the bearing setup. But no doubt it's a time proven method, and if
you the tools/skills to do it right...great! But I believe rack is
cheaper... and would appear easier for a novice to work with, so I
think I'll probobly end up trying that first. Unless you have a good
low cost design for a rotating nut design!

The issue with the gearing is really more of a problem with servos
than with steppers. Steppers are fine at lower RPM, but DC servos
really want to typically run at higher RPM to develop more HP. But
of course everything is in the details so it really depends on the
specific motor, load inertia, accel desired, etc. There are some
good motor sizing programs avail, check some of the recent posts on
that subject. The thing thats kinda cool about timing belts for
gearing is that if you don't get the design perfect you can "tweak"
the ratios a bit....but you're right, no free lunch in terms of
complexity!

THANKS LES WATTS for the pointer to Grape.... it's a great free
tool! Only problem is I'll probobly play with the design of the
table for another month instead of cutting steel.... ah the plight of
an electrical engineer trying to do mechanical design.

-Craig

--- In CAD_CAM_EDM_DRO@y..., "turbulatordude" <davemucha@j...> wrote:
> Hi Craig,
>
> I have been thinking about the drive more than anything else.
>
> I am now comfortable about the table. leveling by shims. the
gantry, two 3" sq steel box beams, horizontal. Router suspended
> inbetween.
>
> But it seems that gearing a stepper to gain power adds cost and
complexity when a driven lead screw would keep things simple. My
> first unit was a rotating nut and worked well. (probably because
I'm a rotating nut)
>
> Seems two large screws would be easy enough to spin and keep
syncronized. That and the power is inherent in the system witout
> adding additional gerboxes.
>
> Dave
>