NSK rails aren't sliding smooth

[maddios]

Hi guys, I'm assembling parts for my cnc machine right now. I'm getting most of the stuff from ebay and most of the stuff is used.

I'm building my Z axis with NSK 16mm (width) rails Accuracy class P5, they look like they're in great condition, the rails look real smooth, but when I slide the carriages they slide smooth at high speed. But at low speed, especially on reversals, they seem to bind, is this how they're supposed to work (they don't bind that hard, if i push a little harder they "pop" through, or are these damaged somehow. I slid off one of the carriages partly so I could see some of the balls, and it looks like there's a ball or two missing fro every carriage, I'm assuming that this is intentional (all 4 are missing about a ball). Also I'm assuming this is happening when the balls go into the recirculation chamber, or return to the rail edge, could it be one of the balls is broken?

This is my first mini rail (the other rail I got is a HUGE rail, and those carriages are real smooth) and I'm not really sure if this is normal.

Thanks

[maddios]

Actually, I just re-read the ebay auction, the rails are supposedly brand new. They do come with their original inspection certificate.

[ edit: part number on the rail says LY150340ELC2B02P51 ]

[maddios]

noone? I need to know if this is normal so i can let the seller know if it's not.

Thanks

[amishx64]

From what I know about rails and carriages, they aren't supposed to bind at all. New rails and carriages should be able to reverse directions easily with the same (small) amount of force either way. It sounds to me like the carriage is bad.

What you are describing would worry me. I would contact the dealer and get the carriage replaced if I was you.

[maddios]

well, these carriages are high preload, from what i gather, they're supposed to slide real tight, no?

[amishx64]

Indeed, high preload carriages are supposed to be fairly tight in order to damper vibrations, align properly, etc.

What the problem sounds like is what happens when you reverse the carriages. They run smoothly in one direction but then become stiff in the the other direction then 'pop' and become normal again. It sounds like you have a foreign object in with the ball bearings. It is probably rubbing against the bearing and the bearing casing that houses the bearings.

If you are comfortable with opening them up, you could find a way to clean the bearings off, remove the oil in both the bearings and the carriage itself, then reassemble and add new oil.

If you don't want to do that you could always try and return them.

A third thing that might work is running the carriage down the slide back and forth very quickly in hopes of dislodging the assumed foreign object. This may take about 50 -100 passes easily. You know it will have dislodged when you have no more 'poping' feelings in the carriage. Take the carriage off and clean out the tracks of the rail.

Hope that helps.

[maddios]

hm, these are brand new, i broke the seal on the slides (they were in heat sealed tube bags) But i'll give it a try, try reversing them over and over

[amishx64]

Now that you mention you broke the seal, I think that something may have gotten in there after you opened it or the carriage is just plain defective.

Tell me how reversing them over and over turns out for you.

Good luck.

[maddios]

well, i mean, there are 4 sliders, and all 4 of them are sticking on both rails (2 on each rail). I really doubt i could have gotten dirt into all 4 at the same time, i never even put them into anything dirty, just on my desk, to try to slide them, and back in their bags/box.

I'm going to try moving them back and forth, maybe they just need to be broken in a little.

[amishx64]

Its hard to imagine all four are bad or dirty at the same time. I agree breaking them in is probably the best thing to try at this point.

If you have strong enough motors, a little bit of stick on the carriages/sliders isn't going to hurt a thing.

[maddios]

yeah i have 305oz" motors, using the hobby cnc pro board. so i don't think i'm going to have an issue with this. these slides are also going on the Z axis, so there's very little movement there in the first place.

Thanks for your replies, they helped me think it through

[amishx64]

Hey no problem. Good luck on your machine.