THK HSR35 woes

[Corvus corax]

I just received a slightly used HSR 35 rail and bearing assembly, off of Ebay- and though I can find no outward signs of damage, the movement is somewhat less smooth than I expect from such an expensive setup. I figure the whole assembly should move under its own weight when vertical- this is important, as I intend to use this assembly on my Z axis. When horizontal, the assembly moves fairly easily, but is noisy. When raised to vertical, it jams. There appear to be several balls missing from the carriage, as I assume there should be no gaps. The rail shows no signs of wear, and aside from the missing balls, the carriage looks very clean as well. Are there supposed to be visible gaps in the lines of balls (3 or more balls long)?

[cbass]

Could be preload. Try pushing down on the units and see if they move more smoothly.

As for ball count, I have no idea, though I'm inclined to think there shouldn't be a gap of three balls.

Carlo

[JRoque]

I think Carlo is right on. I had the same result from new rails and trucks. When pressed down a bit, they run very smoothly. You might also want to try the THK grease they sell on their website.

JR

[mxtras]

The preload and the seals and wiper keep the trucks from moving freely. I think what you are seeing is normal - sounds normal from what you have described.

There is always some space between the balls - 3x? I am not sure of that - I don't know what the space is supposed to be.

Grease - use a very light bodied lithium. DO NOT use regular grease - it is too thick and will prohibit the balls from cruising down the re-circulation channels freely.

Scott

[Corvus corax]

Thank you all for the advice, especially on the grease. these have some fairly heavy grease on them now, and after inspecting the balls under magnification, i've found some light scoring on them. I am still of the opinion they are missing balls, especially since the number doesn't match from one circuit to the other, and the top circuits, which are completely enclosed, have no gaps in the chain of balls, hence- no balls missing. When the rail sticks, it does so intermittently, and when pushed hard enough to get past the obstruction, crunches loudly, and then moves suddenly. I measured the amount of force with a small electronic scale, and the rail resists with about 17-20 pounds of sticking force before the rail breaks free. Something is definately wrong. I'm ordering 100 new .250 balls this evening, and will replace all of them after flushing whatever grit is in the system out. Hopefully, that will clear out the debris that has gummed up the works.

[mxtras]

Sounds like a good plan!

On the grease - use the right stuff. I learned the VERY expensive way not to just use "whatever ya got" ($18,000+).

Scott