January 26, 2021

Public Service Announcement – Mikini Ballscrew Lubrication (missing)

3 min read
Anyone still lurking in this forum may find this educational. I think I’ve read every...

Anyone still lurking in this forum may find this educational. I think I’ve read every single post in this forum and haven’t seen mention of what I found tonight.

I’m in the process of overhauling my 1610L (again). The eventual build details aren’t important now… what is important is that I’ve just discovered a serious design flaw in the lubrication system.

Anyone with a Mikini (and possibly Skyfire) knows that the oil pump is located too high and it siphons out the oil. Easily fixed by lowering the pump a bit, but that isn’t the issue I found today.

What I found during disassembly of the table and saddle is that there is no provision for lubricating the X/Y ball screws or nuts.

This isn’t a Chinese QA/QC problem where someone forgot to install some line. There is simply no way to install a fitting (oil, grease, whatever) in the ball nut lubrication port.

All the trucks have oil lines, as does the Z-axis ball nut. But the X and Y axis ball nuts have no lube.

I don’t know if this affects all Mikinis, all Skyfires, or just early ones. Tony (other disassembly thread) has HiWin rails on his and a few other details are different. I believe mine is earlier (2009ish) and has AMT rails and screws. Perhaps this is just an early FUBAR that got corrected like the Z-axis stepper coolant sump – later models were open below the Z-motor; mine is not and my stepper was submerged in 3/4" of goo.

Good thing I slobbered a handfull of grease on the screws when I first bought it a few years ago. The ball screws are indeed ground (not rolled) and arew very nice name-brand (PMI/AMT). Not cheap to replace.

Now I have to figure out how to modify the saddle to gain a bit of clearance for some fittings. I’m tired of tram oil in my coolant, so I’m switching over to grease with remote zerk fittings. We’ll see how that works out.

Suggest anyone with a Mikini or Skyfire pull your way covers, get a mirror and a flashlight, and see if there are any oil lines to your ball nuts. If not, grab a handful of lithium grease (no moly) and goop it up.

If you have oil lines (or fittings, or any method of lubrication) please take a photo and share it here. I’m very curious if this was ever corrected.

Hope this helps someone..
-Ralph

Z-axis ball screw and nut. Note the oil line fitting.

Bottom of the saddle. Note all the line to the trucks…but no line to the Y-axis ball nut or housing.

X-axis ball nut as-installed. Lube port is on the bottom in the photo (hidden). The little hole on the top is a grub screw to hold the seal in place.

X-axis screw removed from saddle.

Y-axis – same thing. No extra holes, no clearance for a fitting.

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