Linear rail trucks have a pair of ball bearing circuits, one side open so they roll directly against the rail.
They are prone to contamination. The wipers try to isolate the inside grease from the crud on the rail. But if you look from below, the bearings are directly exposed to dust.
Guides- even official ones from equipment mfgs- keep giving misinformation- greasing the rail does virtually nothing. The actual rail mfg instructions I read from Hiwin didn’t say to do that. The wiper keeps it from mixing with the grease inside. It gets pushed along, rapidly collects dust, turns to mud that can stick and the wiper may not be able to swipe that out of the way. And only a small part of the rail’s sides is even the contact line. And the main problem may be that the grease inside is contaminated and turned to mud inside. It needs to be flushed and relubricated with a specific type of lithium soap grease (not white lithium lube)- always added by pushing into the truck through the port, not onto the rail.
Dorian didn’t have Zerks, just a grub screw. I did get the specific grease for it. It’s a matter of putting a towel under it, remove the grub screw and be very careful not to lose it, get a brake cleaner straw tight in the grub screw hole so it will flush out the old crud under light pressure which will gunk up the towel. Clean the rails with alcohol and paper towels completely but do not apply more lube there.
Then, you don’t actually need the pressure of a grease gun, just a small grease syringe with a plastic straw that both goes inside the grub screw hole and create a light seal against the hole’s wall to push a few ml of grease into it. It’s open inside, you don’t need much force but you can’t get anything in without a syringe with some sort of seal.
When you roll it, it will transfer grease out in a very thin layer on the actual contact surface automatically. Then push more in to top it off and put the grub back in.
The special Hiwin grease and the syringe setup are still up there, but I don’t know if that will fit the rail trucks’ grub screw size on the CNC.
The zerks seemed essential at first, but now they seem more trouble than they’re worth. They require a specific metric grease gun loaded with the right grease, and a lot of clearance to fit onto the nipple, but it just doesn’t need that much pressure.