[moonblack]

First of all let me state I'm a newbie on the cnc world, just in case it isn't obvious.

I just received some MGN12 linear rails I bought on aliexpress for a mini cnc project, like the one in this auction http://www.aliexpress.com/item/Promo...511040875.html.

I just tested them by hand and they are very "sticky" I can't imagine the nema17 motors I'll be using to be able to move them at all. This is the second time I have this kind of behavior, the first ones I bought for my wood router (SBR type linear rail) were also not smooth at all, for those the vendor sent me three new linear carriages that were better, but not "perfect".

Is this something normal, and how can I have rails that are smooth enough when moved by hand ?

Do I need to clean the linear bearing carriage and oil them again ?

I would imagine that those stay a lot of time in a warehouse where they could become sticky. Or a I'm just receiving bad parts ?

Thank you.

[bhurts]

Are they sticky before you bolt them down? If not then the problem is you are not aligning them properly. As for nema 17 motors for a cutting machine. Probably better to go with 23s now before you regret it later.

Ben

[moonblack]

Yes before I bolt them, I just received them and tried to move the carriages around and they stick like hell. I read a little about it, it seems that it's the preservative oil/grease they put at factory, but I can't see a consensus on how to clean it and what to put back after that.

It's a very small router for pcb engraving, I was thinking nema23 would be a bit overkill.

Paulo.

[jfong]

Just wipe down the rails to get rid of any excess grease on them. Depending on the preload of the bearings and what I call stiction from the grease they will be "sticky" on the rails. My THK linear bearings are like that. You can hold them vertically and they won't drop. Once you put a load on them, they should move very smooth. If they still don't than something is very wrong.

I'm not sure if your bearings have wipers on them but if they do they will add a little bit of friction too.

[moonblack]

I'll wipe them with a lint free tissue and see if they become smoother, I don't think they have wipers, see picture.Attachment 272690

[Falcon69]

If they are preloaded, they may feel 'sticky' when trying to move by hand. I have some 30mm ones I plan to use for my build, and they are 'sticky' to move by hand because of the preloading. Also, as mentioned, the grease that they are shipped with to help prevent oxidation and rust will also not help for the movement of them and will make the linear bearings appear and feel 'sticky' even if they are not preloaded. I would clean them, but don't do it until you are ready to install. That grease from the factory is on their for a reason, to keep them from rusting and/or oxidizing.

[moonblack]

Thank you all for your replies.

@Falcon what should I put on them once they are cleaned, to prevent rusting and/or oxidizing when they are installed on the router ?

Would white lithium grease be appropriate ?

[ger21]

Don't put anything "on" them.
Just grease them on the inside, through the grease fitting.

[Falcon69]

Not sure on that. Anything you put on it will most likely be scraped off by the scrapers on the bearing assembly. If You plan on leaving the machine for awhile (long extended time of no operation, or short stay if the area machine is in is prone to moisture, like salt air from east coast), then you may want to wipe it down with some grease. Long extended period I'm talking about is like several weeks. Do what you can to prevent rust build up. You don't want your rails or Bearings pitting do to the rust.

Normal operation of a couple hours a day, or even a few hours a week should be okay. As the bearing glides over the rail, it will leave a residue of grease, which will help to protect it.

When I was working in a shop that had an industrial size CNC machine, part of my job of operating the machine was that I had to grease all the zert fittings once a week, regardless if it needed it or not. You will find that the bearings themselves you will need to grease often.

[moonblack]

I'll go from here, and as they say nothing's better than experience, so I'll follow your advices. Once again, thank you for all your replies Gents.