Re: [CAD_CAM_EDM_DRO] thermal expansion

The real issue is certainly ballscrew heating on the
larger gantry machines. We had a pretty good thread
a while back, so I won't rehash it. It can't really be
ignored on longer screws. The bottom line is:
with fixed- fixed end bearings one end must be able
to float axially a little. A duplex pair of bearings with
a push fit in their housing is what I use. It is very
lightly spring preloaded. The forces generated
by a tensioned fixed mounting are absolutely huge
even with a few degrees temperature rise. Kind of like
ice forming in rock cracks and splitting them...

We have some numbers on the phenomenon in the
thread.

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: "Jon Elson" <elson@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, January 28, 2003 12:16 AM
Subject: Re: [CAD_CAM_EDM_DRO] thermal expansion


>
>
> Greg Jackson wrote:
>
> >There are quite a number of machines which run hollow columns and flood
them
> >with fluid. It can be pumped throughout the machine and controlled with
a
> >small thermostatic heater. An easy way to solve frame motion. Ball
screw
> >growth is different, but big machines will normally stretch them which
> >reduces much of the thermal growth factor. I think you need a pretty
beefy
> >frame to provide any significant tension on the ball screw.
> >
> >
> Some machines have hollow ball screws and run constant temperature
> coolant through them to
> prevent thermal changes. The same is often done with spindle assemblies
> for thermal
> control. These are clearly high-end machines.
>
> Jon
>