[Guldberg]

Im in the process of making a slant bed cnc lathe from scratch up, involving, amongst other, some THK ballscrews bought off ebay. I can tell that they have been lubed with some white grease, but im thinking of changing to oil instead. This way the can be connected to the overall lubrication system. I have two questions now:

Should I replace the grease with oil in the first place, or should i just refill it with some more grease?

If I do connect it to the oil lubrication system, can I just flush the ballnut with a lot of oil to get rid of the old grease, while I run it back and forth the ballscrew? I may be able to remove the protective sealings.

[Guldberg]

Nobody tried to re-lube a ballscrew?

[LeeWay]

My ball screws were either new or had oil to start with. I did just add oil to the used screws. I don't fill the nuts in the used screws as I should though. I simply apply to the screw and let the nut pick up what it wants. I oil them weekly, sometimes twice a week depending on usage.
I need to add oiling systems to them all.
I personally think oil is a better solution as grease can hold dirt and chips inside, where oil would at least tend to work it back out.

Some nuts have grease fittings. Some have oil ports like my used ones do. Others have nothing. On those, I just add oil to the recirculating tube holes. Works pretty well. No signs of wear on any of mine yet.