Linear rails dont run smooth

  • Hi,

    I recently bought some THK brand linear rails used on ebay. On first look they made a good impression, no scratches on the rails, no wobbling in the wagon, just a bit tight and I felt some little resistance here and there. So I went on cleaning and greasing them like I've done before with the cheap Hiwin clones. I used WD40 for cleaning and I have some grease that a friend of mine uses as a prosthesis technician.

    I carefully took the wagon apart and flushed the old grease of. No dirt, or metal pieces in sight, so that looked promising.
    I tried one wagon just on WD40 and one I regreased and they both run quieter and smoother now, however I can still feel that some individual balls don't completely run smooth and all wagons are too tight to move on their own under their own when when put vertically.


    I also noticed that the bearing cages are not connected, they are just bands that hold the bearing-balls. It's the same on all carriages, so I don't think they are broken, but when I push the bearings along without the rails inserted there is more resistance when the open end of the cage has to go around the sharp turn at the ends of the wagon.

    Can someone tele-diagnose this or give me some pointers?
    (I tried to get the THK customer service on the line but I can't register without a business there.)


  • Hi,

    Linear rails come in all kinds of quality.

    I am working on a printer and I used 4 Inverntech brand rails. I normally have had good results with them.

    Not this time.

    A couple of them "crunch" a lot when moving the carriage. I wasn't in the mood to try to improve them so I took the plunge and have 4 Misumi brand replacements on order.

    I am looking forward to comparing them.

    In any case, when it comes to low cost rails, I think the reality is that you may have to purchase extra units just to find enough good ones.


  • @sungod3k One thing you can try after solving the sharp-turn problem is to change the fitting between cartridge and rail by using smaller balls. My preferred shop is Kugel-Winnie. They have tolerance classes, G3 and G5 best, then G10 to G16, G20 to G100 being still precision.

    I suspect your seller used cartridge and rails which were not sold together newly. If you give me exact images of rails and cartridges and type description, I can compare them to my THK. I have different types of them and they run smoothly. You can google images of your type also and look at the profile (front side) of the rail especially, whether it fits.

  • @JoergS5

    Its the thk srs 9xm type.

    I was considering buying some new balls, to exclude the possibility of the balls being bad. Ill check out kugel winnie 🙂
    Although the guy who sold them to me said they were only used in a cover and haven't seen much use, for whatever that statement is worth.

    Also, now the morning after I'm noticing that they already run smoother than yesterday. Maybe the solvent from the wd40 evaporated and the grease settled in all the nooks and crannies.
    and one carriages makes a repeatable click that the others don't make, maybe I replace the balls on that one and see how that's going.

  • check out the inner ball tunnel.
    they are drilled from both sides, and if they dont alight properly there is a small groove that causes problems. in that case there is not much you can do.

  • @Veti this i checked, the bearing ways are absolutely smooth

  • @sungod3k From THK 9 I have only type RSR9ZM, so I cannot help comparing the images, and they run fine. The linear guides may need a day to run smoothly, so running it some time may be already the solution.

  • Me, personally, I'd get that WD40 can as far from any precision machinery as possible. WD40 has its uses; cleaner/lubricant is not among them.

    I'd clean them with a light oil, followed by an actual solvent for the oil. Or an oil designed for cleaning. I tend to use "CLP" (Clean Lube Protect) brand in the USA. You appear to be in Germany, so I am not certain what is available. Maybe Ballistol?öl&language=de_DE&qid=1574124687&sr=8-9

    Then, re-grease with a grease intended for metal-to-metal pressure contact. Something like:


    If they still are still not smooth after this, then there is a mechanical problem.

  • In my case I baught 15 m in rails for ~25 € per m from different sellers (ebay, Aliexpress). For me, they all looked as if they were in use already. I think, this is the reason why some of the carriages scratch more than they slide..
    Theoretically, they all require maintenance. On the other hand, for 25€ per rail and 2-4 € per carry it might be not even worth it. Just buy another one.

  • did you wash everything with wb 40 before you apply any lube???

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