Acme screws and pre-load nuts was:Re:Re:greetings

Dan Dowell asks,

>Here I go again. Whats a preload nut? Would like to see one.
>THANKS Dan

Dan,

We'll try some more ASCII art.


|--------| |--------|
| |00 0 0 0 0 00| |
_| _ _ | _ _ _ _| _ _ | _ _
/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/

Acme screw shown (could be ball or vee)
_ _ _ _ _ _ _ _ _ _
_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_
| | | |
| NUT |00 0 0 0 0 00| |
|--------| \ |--------|
\ \ \
\ \ \____Pre-load Nut
\ \
\ \
\ \___Pre-load Spring
\
\___Fastened to the machine

So, what are we lookin' at:

1.There are two nuts on the screw.
2.One is fastened to the machine(labeled NUT, above)
3.The second one is not fastened to the machine,but is PUSHED AWAY
from the first nut(by a spring, shown with the 0's,above)
4.The second nut is not allowed to rotate independant of the 1st NUT.

The two nuts are pushing outward against the flanks of the acme
threads with the force of the spring. As long as we don't push on the
assembly more than the force of the spring can resist(the pre-load),
we have created a rigid nut with no backlash when changing
directions.

In practice, the two nuts are "keyed" to each other, But only one
connects to the machine.

Ballendo

P.S. Nowadays there are more elegant(and effective) means than the
spring shown here(cams, for one). Look up KERK and Ballscrews and
actuators to see examples of these. Belleville washers are commonly
used in BALLSCREW nut assemblies.