On my delta printer I have linear rails and one of them (rail+block) started squeeking while printing. I have thought about these causes: 1) the rails are not lubricated well enough, they were always lubricated from the outside (grease put on rail) since the instalation about 4 years ago 2) they are wearing out and need replacing.

I have couple questions about both possible causes.

The everlasting question: which lubricant do I use? I have seen many to use grease and many others discouraging from that. If not grease, what else? I have Konkor 101 (might not be available in English) or WD40 as lubricant oils.

Should I remove the block from the rail, clear both and apply new lubricant from the inside (i.e. on the inside of the block, to the steel balls)? Or is from the outside enough? (I supect it is not.)

If the rail and block is failing, which one of them? I mean, most parts are designed that some fail sooner than others because they are easier to replace. Is the block wearing out (because it is more delicate) while the rail is still holding (because it is essentially just a block of metal)? Therefore replacing block could solve the problem?

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    $\begingroup$ WD-40 is not a lubricant, but that discussion can be found elsewhere on the internet. :-) If the rail is wearing out (the balls are hardened), it is probably a low quality rail. There is an enormous price difference in good and bad quality rails. Manufacturers of good quality rails provide a grease nipple on the carriages to grease the bearings, but light oil should work also. $\endgroup$ – 0scar Mar 28 '20 at 21:38
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    $\begingroup$ WD40 is short for "Water Displacement - formula 40". It's designed as a cleaning agent and to get water out of applications that are to be greased or to prevent them from rusting. $\endgroup$ – Trish Mar 28 '20 at 21:57
  • $\begingroup$ The carriages have a hole on both sides but no screw/nipple. I also found in multiple sources that WD-40 can also be used as lubricant, among other use cases. However, I have found out just now, that it was not the rails nor carriages squeekeng but the magnetic rods from the carriage to the efector. But that is for a different discussion. $\endgroup$ – MStarha Mar 29 '20 at 8:40
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    $\begingroup$ WD40 is a short term lubricant, not a proper machine oil or grease. It is called a "Kriechöl" over here - used to creep into rusted or stuck machinery to lubricate it for disassembly. NOT for permanent lubrication. $\endgroup$ – Trish Mar 29 '20 at 10:57
  • $\begingroup$ Thanks for clearing that out. Apparently, there is a lot of missinfromation out there $\endgroup$ – MStarha Mar 30 '20 at 7:22