Z axis LM12UU bearings sticking

I have been printing a few days now, but I have an ongoing problem which I think I have diagnosed.
When bringing the Z axis down the arm often gets stuck, the motor turns and it pops the nut out the bottom of the mount on the Z. This then mucks up the Z compensation.
I tried oiling the vertical rod, but no help.
I removed the threaded rod and manually moving the X arm up and down the bearings stick in atleast 3 places.
Inspecting the rod shows its fine, no marks, straight.
Then I removed the vertical rod and bearings, put loads of oil inside the bearings, manually slid them along the rod dozens of times, let oil drain out, but still the bearings seem to stick, one feels free-er than the other.
So I presume the bearings supplied are not great quality.
I have a couple of IGUS items on their way to me (I deal with IGUS through my company) to try.
Only concern I have is that websites lists the LM12UU as 21mm OK, 30mm long, but the IGUS parts are 22m OD and 32mm long. So I'm not sure they will fit in the carriers.
I'll report back when (if) they are fitted.

Interested to hear if anyone else has a sticky Z

Hi Balidey,

not noticed this on Z (though I did get some Z binding when I replaced one of the Z runner bearings to tightly on the X arm) - however I did notice when comparing my new (plastic slide) Y frame to the original (LM12UU on smooth rod) that the original's movement is a lot freer away from the Y motor than towards it - I'd noticed that before but had put it down to the motor or belt - now the frame is free (just the plywood frame and MDF sitting on top of the bearings and smooth rod) it takes much less effort to move away from the motor than towards it (it's also quieter moving toward the motor) - maybe the balls aren't recirculating so freely in one direction?

Ray

Brief update.
IGUS bearings RJM-01-12 LOOK the same as an LM12UU, but the outer diameter is 22.5mm, the LM12UU are 21mm, so I am not even going to try and put them into the Z bearing carriers. But I may try printing another pair with larger holes to suit. Eventually I would like to replace all the LM12 on my Ormerod with IGUS dry bearings.

Just tried lifting the X arm up manually, removing threaded rod and lowering it, the arm sticks in about 3 places, so I am sure that the bearings are at fault, even after liberally oiling them.

ETA: Just realised, the LM12U on the Z are tight against the acrylic X arm, so I can't increase the diameter without upsetting the relative positions of the X arm and Z rod etc.
So, looks like I'll just source some new LM12UU and see if they are better quality and don't stick.

Edited 2 time(s). Last edit at 03/12/2014 08:04AM by balidey.

Often the cheaper linear recirculating ball sliders have bits of crud in them so before I ever fit them, I wash thoroughly with either IPA or paraffin and then oil them with a high quality spindle oil, such as used in the spindles of surface grinders, can't remember the number offhand but it's easily found. Usually makes the cheaper unit slide more freely but they are "cheap" for a reason though sometimes even quality ones can get stuff in them. I would add the ones with my Ormerod were fine, but I did follow the above routine first.

I had a failed print last night. The Y axis front bearing got stuck.

Ive put some 3-1 oil on the runners and have managed to free it up but dont know how long it will last!

Quote
jhkiom
I wash thoroughly with either IPA or paraffin.

The only IPA I know is India Pale Ale, and I'm not wasting that on my bearings!
I use Graphite Lock Lube
Greg

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Ormerod #17

Ha, though in my case I'm sure you know it's isopropyl alcohol..........my first pint was a double diamond in 1971, cheers