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

Jon Elson <elson@...> wrote:

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.

// I must have an unusual one, just looked at it again and thats how it is. Possibly thats how it looks and I think it is and its actually not. The toothed belt hub threads on one end tightly against bearing and is secured by setscrew or rollpin. Either method would have the same result. I do recall one endplate containing two bearings (servo end) and the other only having one. In retrospect, it must have a shoulder on the far end that the bearing heels against. Because the handwheel hub on the undriven side just slides on the shaft up to the bearing and overtightening the handcrank nut would push/pull the endplates out of square with the table. My retrofit was originally done by no telling who and I'm sure different builders had different ways of preloading. I turned my ballscrew around to get the ridiculously long servo out of the aisleway and potential path of the hi-lo towmotor. What a nightmare that was to re-assemble. Little balls everywhere. .///

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



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