Re: [CAD_CAM_EDM_DRO] How does one adjust Ballscrews on a Bridgeport

R Rogers wrote:

>
>Stephen Wille Padnos <spadnos@...> wrote:
>
>they
>feel "springy". If I lock the table and push the handwheel, it turns a
>little (around 8-10 mils, according to the dials). If I let go, it will
>spring back to where it started. It gets harder to push (like a
>spring), until eventually I overcome the table lock friction, and the
>table moves.
>
>Steve, Thats deflection, not backlash. Backlash would display a deadspot of resistance in the handcrank. If it has gradually rising resistance in both directions axially on a locked table that is definitely deflection. Tightening the nut on the handcrank has no effect on backlash its merely to hold the handcrank hub against the outer bearing and keep the handle on, all the backlash adjustment is attained between the two endplates.
>

No, Bridgeport, and most other machines with rotating screws and fixed
nuts use a double bearing
at one end, and a "simple" bearing allowing some axial travel on the
other end. This is to allow
different thermal expansion between cast iron and steel, without any
possibility of bowing the
leadscrew. One machine that does use the double fixed ends is the
Bridgeport BOSS, where
the leadscrew is bolted firmly to the table, and the nut rotates on a
set of bearings in the
saddle.

So, normally, all preload is between two bearings that are within an
inch of each other.
That way, temperature has no effect on preload.

Jon