Re: [CAD_CAM_EDM_DRO] size of leadscrew question

In a message dated 12-Mar-02 11:37:43 Central Standard Time,
rcav8r@... writes:

> The table I have in mind will have a 48" cutting length X axis, so figure 5
> to 6' long. Could I substitute a 1/2" leadscrew with 10tpi and 2 starts?

John: You asked, so here's M.H.O: NO WAY, unless shorter than 20"! Ever
hear the term, "Rigidity"? The "flopping" of a lead-screw of insufficient
rigidity for its length at whatever speed will cause unpleasant effects,
ranging from insignificant perturbation of the tactile sensors in the
operator's finger-tips, to inaccurate, unrepeatable, expensive effects upon
the manufactured goods so-produced.

The 3/4" dia. you mention seems to me like a very-MINIMUM for 4-foot screws.
I would design for 1" dia., and use 7/8" dia. only if that were all their wuz
inna world close to that, at least at the moment of design-decision. I built
an X-Y table with a 5'x10' working-area in '85, and it used 1.5" dia.
ball-screws, and, wow, when I ordered the screws I wondered all the time if I
had done right by using "their" engineering-data and charts to determine the
screw-section. Cost $800 for one 12' screw with preloaded ball-nut. Once
all-done, I could sense by "feel" that I'd not feel at ease, were they only
1/8" smaller in dia.! The people who have been DOING that for so long are
the ones to ask, not home-brewers with an attitude about spending more
hard-earned/stolen money for something more expensive just because "some book
SAYS to"!

Ball Screws & Actuators in San Jose, CA must be really GOOD folk (if they'll
sell to ME!), so, look 'em up on the net (sorry, I can never remember their
web-address.


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