Re: [CAD_CAM_EDM_DRO] rolled ball screws

I use the oversize ball preload rolled screws on my gantry. Specifically
it is the HIWIN 25mmx5tpi.

You are right in that they are very economical. And accurate- mine mapped
out with max 0.003" max ABSOLUTE error over 5 feet at 75 degrees F.

Mine is an indusrial application, but I have only a hundred hours or so on
the
machine. So far... they are fine. I am getting about 100 lb per thousandth
stiffness at the spindle. That is better than my Index vertical mill.

It is my understanding from talking to the HIWIN engineers that oversize
ball
preload is very stiff but is four point ball contact. As such the balls are
prone to
scuffing and somewhat faster wear. I still expect at least hundreds of
kilometers
lifetime though. For industrial that might be a couple or few years. For
hobby
stuff it is forever if they are kept very clean.

I did notice a 50% reduction in preload drag torque after about a 10 hr run
in...
but I cannot say it is the ballnuts. I suspect it is just the transmission
and end bearings
seating as I know they create most of the drag torque from my measurements.
There are 16 5% preloaded bearings in my x axis alone!

Les

Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.alltel.net/~leswatts/wattsfurniturewp.html
engineering page:
http://www.alltel.net/~leswatts/shop.html
Surplus cnc for sale:
http://www.alltel.net/~leswatts/forsale.html

----- Original Message -----
From: <tacman@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, January 07, 2003 9:31 AM
Subject: [CAD_CAM_EDM_DRO] rolled ball screws


> Hi,
>
> I am in the process of building a small CNC mill and would like to use
> rolled, preloaded ball screws and nuts. The cost of these rolled
> components is not much higher than Acme screws and nuts. The ball
> screws are preloaded by placing larger balls than usual in the nuts to
> take up any slack.
>
> Does anyone here have any experience with these types of components?
> How well do they maintain zero-backlash over time? How long does it
> take to break them in? Reliability?
>
> Thanks
>
> Steve