[electrosteam]

I have a THK 3210B ballscrew off a turret mill X-axis in pieces for cleaning.
The balls are 6.365 mm (as measured with a precision DTI on a test stand calibrated against precision blocks) and pitted, so need replacing.

After cleaning, with the screw vertical and lubricated with ISO 68, the nut will rotate by gravity end-to-end.
This amount of free running seems excessive.
I have seen videos that demonstrate the nut stopping in a couple of revolutions after a manual spin initiation.

I did a trial load of 6.35 mm balls (1/4"), the nut drops under gravity when dry.

What size then should I purchase ?
I am in Sydney and 110 balls of 6.370 mm from a reputable supplier in the US will be about AUD 200, a significant amount.

Can anyone comment on the effect of increasing ball diameter by 5 micron ?
Should the increase be less ? or more ?

John

[electrosteam]

Did a test with the nut clamped horizontally in the vise with approx 500 mm of the screw on either side.
A DTI shows the screw has +/- 50 micron vertical looseness at the ends.

This possibly indicates that an additional 5 micron in ball diameter would reduce the vertical looseness to zero.

Still looking for comments from others as to the effect of changing ball size.
John.

[electrosteam]

Spent a lot of time to determine the old ball size was 6.365 mm.

Loaded the nut with 103 old balls plus 3 off 1/4" commercial balls.
Clamped the screw to a mill table using V-blocks with a DTI detecting horizontal nut movement.
Nut pushed/pulled to get 25 micron backlash.

When got to the point of money (AUD 300) for new balls, got cold feet, and ordered 6.3685 mm balls from Bal-tec in CA.
Larger by 3.5 micron.

Loaded the nut with 106 new balls lubricated with shipment oil (very light).
Nut is reluctant to start rotating when ballscrew held vertical, but continues to rotate if started by hand.

Repeated the mill table test and got 18 micron backlash measured.

Called it quits and started the ballscrew installation on the mill.

John.