Best ball screw prices? (was: Ball screw load ratings)

Well, after further review I agree completely. I've decided to buy
the Thomson Saginaw 5/16" .200 lead ballscrew and the preloaded ball
nuts.

Does anyone have a source whose price is significantly (5%+) less
than Thomson's? All I found so far is Reid Tool, and they're a few
cents cheaper.

Thanks,

Jeff

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <jmelson@a...> wrote:
>
>
> Jeff Swayze wrote:
>
> > I'm in the process of choosing a ball screw (or lead screw) for a
CNC
> > retrofit of my mill/drill. Can anyone suggest a value for the
maximum
> > axial load such a ball screw would see? I would think only 100
lbs.
> > or so, but I really have no idea.
>
> On my small Bridgeport, the servo drives for the X and Y axes can
develop
> 1000 Lbs of linear force at stall. You can figure out the forces
involved
> in cutting operations by converting motor HP to torque applied at a
radius
> at some speed. For low speed operations with larger diameter
cutters, the
> linear force applied to the workpiece becomes substantial.
>
> > If the value is low enough I can use a modified acme screw with an
> > anti-backlash nut (up to 125 or 250 lbs. depending on the style)
and
> > will save much $$. Otherwise I'll have to go with a ball screw and
> > preloaded nut.
>
> I wouldn't try this. You will have very rapid wear of the nut and
screw
> if you try to preload an Acme screw. An adjustable but locked Acme
nut
> will work for a while, but eventually the central part of the screw
will wear
> so that it is looser in that region.
>
> I would think that a screw designed to hold at least 500 linear
pounds of
> force without bowing would be the minimum on your machine.
> You need to keep in mind this includes table friction, inertia,
cutting loads
> all summed together.
>
> Jon