Re: [CAD_CAM_EDM_DRO] Many Thanks to the group & "Z axis counterweight

Hi Peter,
Many thanks for the info, it does help a great deal.
Many thanks again.
I know some companies install spiral bevel gears that reduce the backlash on
the knee,but I've
not found any at this time. I guess I may not need them.
Yes I would like to see photos of the knee ball nut.
Thank you,
Al Alfano

> Hi Al,
>
> Yes, I did replace the knee screw with a ball screw - from Rockford Ball
> Screw. It's a 1.25" ballscrew with a single ball nut fitted. The
> reasoning (based on judgement plus input from others) was that there
> would always be some downforce load on the knee so backlash in Z axis
> would be much less an issue than X or Y where I used double ball nuts
> for zero backlash. I had to mill clearence to one side of the knee
> support column in order to correctly fit the ball nut. I can post a pic
> if anyone is interested. No, I didn't replace the bevel gears on the
> knee (but did consider doing so) all I did was by trial & error add a
> couple of thin shims under the large bevel gear to ever so slightly
> pre-load the gears and reduce play. You know you have too much pre-load
> when turning the knee crank causes a cogging sound. Mine is snug, with
> minimal backlash less than a thou.
>
> I chose to fit the gas springs near the front of the knee because by my
> (misguided?) thinking at the time, I felt this arrangement would provide
> a better balance of the various forces. I realize now the knee isn't
> really cantilevered so my assumptions may be wrong. However, before I
> fitted the gas springs, during a rapid Z move (over 48 IPM) I did notice
> a horrible vibration sound which I suspected was the Z axis gib
> vibrating. I played with the gib/way tightness and could reduce the
> vibration but not eliminate it during a rapid move. After fitting the
> gas springs, the problem went away completely.
>
> Hope this helps.
>
> Cheers, Peter