Re: [CAD_CAM_EDM_DRO] Re: spinning ball nuts

To: CAD_CAM_EDM_DRO@yahoogroups.com
From: "plastiguy" <plastiguy@...>
Date sent: Sun, 08 Feb 2004 03:24:21 -0000
Subject: [CAD_CAM_EDM_DRO] Re: spinning ball
nuts
Send reply to: CAD_CAM_EDM_DRO@yahoogroups.com
Scott

If you are concerned about the span.
Have Sliding Support Bearings. The support bearings would
be slid along under the shaft by a cable hooked to the Gantry.
Going in one direction, the cable would pull the bearing along
as the gantry moved away from it. Going the other direction,
the cable would be slack and the Gantry would push the
bearing ahead of it. The cable would make sure the shaft
never had more than the cable length of shaft unsupported.
You would have a minimum of four Sliding Support Bearings
on the two Gantry Screws(one axis) . I

Bob
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> That "design challenge" will indeed be the "SNAFU"! I still think

you will

> need AT LEAST a 1.25" O.D. screw! I built such a machine in '86
> (126"-"X-screws") and I DID use 1.5"O.D. x ½" pitch ball-screws.

Expensive, yes, but it

> worked!
>

Jan -Thanks for your help. I'm curious why you think still a 1.25"
screw will be needed. This has HUGE load carrying capability, far
more than the couple of hundred pounds tension (at most) load exerted
on it by moving the carriage , even while cutting. Seems all I'll
want to do is have a screw stiff enough to not sag appreciably when
the carriage is at the extreme either end. And even a little sag
would be OK from a positioning perspective, as the screw would be
"lifted" into place as the carriage (a rigid system, much more so than
any sag seen in the screw)passes by. The need for a 1.25" SPINNING
screw comes from the effect of it whipping like a jump rope at high
RPMs if it's not rigid enough (overcome by upping it's diameter as the
unsupported span increases). I will plan on incorporating a
tensioning rig onto one end of the stationary screw (I'll have a VERY
rigid 2"x4" welded steel box beam machine frame) to hopefully find a
good tension that doesn't deform or unduly stretch the screw while
still offering a straight, sag free push-me pull-me system. Again,
thanks for your insight, and please offer me any corrections if I've
misinterpreted or overlooked anything you've offered. To all other
replies to my inquiry, thank you all. I feel much better about this
approcah with the bits and pieces of your collected experiences. Best
Regards - Scott




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