Re: [CAD_CAM_EDM_DRO] Ball screw cost and sources

In a message dated 5/25/2003 10:42:52 AM Central Standard Time,
acortez@... writes:

> Just wondering about the approximate costs of the precision rolled
> ballscrews and preloaded nuts that would be involved and the names of some good
> suppliers. I'll probably only need about 20" for the X axis and about 12" for the
> Y axis.

Cortez: I have bought precision-rolled ballscrews and ACME screws from BSA
in San Jose, CA (www.bsa.com??? Not sure!). They offer ready-to-use "screw
kits" ONLY for Bridgeport machines and knock-offs. For the little ENCO you
mention, you would need smaller-diameter screws and end-machining. You CAN buy
"cut to raw-length" screws with nuts (never forget! PRELOADED double-ball-nuts!)
and then do the end-machining yourself, IF you are enough of a machinist to
do that turning. It IS a task!

I do not know what the approx. cost for what YOU need would be, if
end-machining were available, but I would GUESS several hundred dollars. Just for the
raw-cut screws with preloaded ball-nuts, for YOU to do the ends, perhaps around
$200? I just don't know!

There are a couple other firms that supply ball-screws with nuts, the only
one that comes to mind right now is Thomson, the same firm that made itself
famous with the linear ball-bearings and hardened shaft-ways. I do NOT have a
clue what their pricing is like for sizes. Probably "up there", as I am guessing
the only screws THEY offer would be very precision, perhaps ONLY "ground
after rolling"?

IGUS? THK? No clue! Sorry! I have built several smallish machines with
ACME preloaded Turcite nuts, but setting the preload so there is no
appreciable backlash on those will result in a considerable "drag" on the screw,
meaning the steppers or servos you use will have to be able to overcome this drag,
PLUS the forces required to move the cutter into the work. But if that is not
a factor for you, the use of ACME screws with those preloaded Turcite nuts can
work fine, and save you Gigabuck$. ONE problem with those
fiberglass-filled Turcite ACME nuts: The abrasion of the microscopically-fine glass-fibers in
it has TWO bad effects: It causes fine "screw-dust" to build up inside the
nut-threads, and the slow removal of material from the screw-steel begins to
become quite noticeable (screws get FINE polish on them where the nut hangs
around!), so the EASE of turning the screw can vary CONSIDERABLY between the
region where the nuts most-often reside, and the "far ends" of the screws! All
this kinda thing is rarely discussed to sufficient degree in the catalogs and
"white papers" that might come with the hardware, so that's why we OLD MEN
sometimes shyly mention EXPERIENCE! There just isn't ANY substitute for that!

Which brings me to a closing OT trivia: Back when I was in my thirties, I
was visiting a 30-something machinist who had perhaps 5-7 years experience IN a
machine-shop. We were talking nuts-and-bolts, as I was dreaming up my first
CNC lathe, controlled by an ancient PET. At one point, about when I had used
the word "ACME" perhaps the fifth or sixth time in the conversation, he said,
"Where is this Acme firm located? I have never HEARD of it. Do they make
anything other than lead-screws?" And he wasn't even embarrassed (or was a
skilled actor!) when I told him that was the common THREAD-TYPE of lead-screw on
manual lathes, etc.!

Hope all this is of use to anyone who reads it! Jan Rowland


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