Re: [CAD_CAM_EDM_DRO] tensioned ballscrew

If I get you correctly, you're talking about adding end pressure to the ends of
the ballscrew, yes? This would result in the middle of the screw acting like a
kids jump rope. it would be better to give a slight pull to the ends of the
screw, instead, as this would tend to help keep it straight.

Bill

On Mon Feb 18 18:19:20 2002, Doug Harrison, <prototype@...> wrote:

>I have two ideas that need to be challenged. The screws on the X axis of my
>router are ten feet long. They are 1" diameter, .25 pitch from Rockford.
>
>1. We have come up with a way to provide intermediate support so as to get
>around critical frequency problems. An extra pair of blocks on each linear
>rail will carry support bushings. These blocks are connected to each other
>through a beam about five feet long. This beam is tied to the gantry
>through a 2:1 cable arrangement so that the support blocks move at half the
>speed of the gantry. Thus, the worst case support is when the gantry is at
>one end and one support block is in the middle of the screw.
>
>2. Now for the end bearing blocks. I want to use a tapered roller bearing
>at each end of the screw and tension the screw between them. This poses two
>possible advantages. First, by tensioning the screw I can further raise the
>critical velocity (though I've been out of college too long to remember how
>to calculate just how much). Second, by varying the tension in the screw I
>should be able to adjust out any first order pitch error (though not second
>order or cyclic errors).
>
>Of course it would be best to have two bearings at each end of the screw, so
>I propose putting a regular ball bearing about two inches outboard of each
>tapered bearing in the bearing block. This would take up radial loading and
>thus improve end fixity of the screw.
>
>I welcome y'alls opinions.
>
>Doug

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