[mobus1]

Hi Folks,
I'm relatively new to this forum and CNC.

I have had the oportunity to dismantle some used low hour automation machinery, and seperated lots of HSR rails from the major bulk of the rest of the equipment. i took off the air cylinders. i have not removed the rails from the mounting blocks of aluminum or steel.
I have left the rail/carriages together for the time being.the units look abosolutely prestine.


the rails seem rock solid as far as play is concerned.
The slide motion is "randomly smooth". I know, please don't laugh.
The trucks can slide back and forth smooth as can be, but every 4th or 5th, or sometime 8th or 9th slide, I can feel very slight effect of the ball bearing movement inside the trucks. If i move the trucks REAL slow, it can sometime be more apparent. There is no play while this is occuring. It almost seems to be an action due to the grease (clean grease, not contaminated). A little shot of WD40 gets the truck sliding easier, but the grease thickens up after a bit and the effect continues. I do have some brand new rails/trucks and can feel this effect ever so slightly on those as well, but not as much as the used rails. Could this be simply just minor contamination of the grease causing a slight vibration, or is this definite signs of extreme wear?

Again, while i have not used a dial indicator to check for play, i can feel no difference between the new rail and used in terms of play, just the rolling ball effect. I have inspected the rails under a magnifing glass, No visible marks or corrosion on the rails.I have so many of these i was going to offer some cheap on this sites classifieds or ebay, but not if they are definitely bad.
I would not hestitate to use these on my planned hobby CNC, but would not want to sell them if questionable.

Any thoughts on this?
should i remove the a truck from a rail, "flush" out all the grease and re-grease?
Thanks.

[lgalla]

Mobus,I have the same effects on many THK blocks and rails which were purchased as new on E-bay.Your description is exactly what I feel.Tiny bumping as if the balls are realining.Don't have an answer,hope someone else does.
Larry

[mobus1]

Thanks, Yes, I think that is a good term; the ball bearing aligning.

I should add a note here which i did not include in the post;

This effect is noticed when both trucks on a dual truck setup are mounted, If I take off one truck the the trucks run smooth. the trucks are on the same rail, mounted end to end.

I will try to add a photo of this setup if the thread will allow it...i've never tried to add a photo the a thread.


Just tried to upload a photo from my computer...the website says uploading, please wait, but photo doesnt upload.
I'm not sure how that works, all new to me. sorry.

[fatal-exception]

I would say that the balls are sliding to fill a gap inside the race.

I had some brand new spindle bearings that did the same thing. Insdead of instantly taking them back, I used them for a day. They no longer do that. Have no reason why...

For linear bearings, I wouldnt worry about it. If you drop a ball out of them, they will do the same thing.

I'm using THK-HSR rails on my latest milling machine, and I can tell you that they are totally sweet. I bought them used, but I doubt they moved much before I got ahold of them.

Paul

[lgalla]

Geez guys now I am checking all my blocks Mobus I am in the same boat.Would like to sell on E-bay but not if questionable.
There is a gap on all my blocks.I assume part of the bumpy feel is from changing direction.
I have 10SSR-15 blocks and short 200mm rails apparently new.No bumping but stiff.I assume they have a preload.Engraved on the blocks is C-1.
My HRW-27 are smooth as silk sometimes,same for the HRW-21.These will slide under their own weight.Again I don't know what is right.Perhaps someone with worn out blocks can post.Do they grind?Or lock up?
Larry

[mobus1]

I had an interesting conversation with a tech a INA bearings today.
He told me that the cleaning of exterior rail grease with a paper towell should not cause the problem i've noted here.

he seems to think it is due to the particular factory preload of my INA bearings in this lot of dismantled automated equipment.
He said they were preloaded extras tiff, and that without a load of the tooling/equipment mounted to them, they may exhibit the symptoms i have reported.
he thinks i should just use them as is and ignore the symptom. he said once they are mounted under load of the axis/tooling/router weight, they will probably smooth out.
either way, he states the symptons should not hurt the bearing.

i personally don't see how this can be, but hopefully some other forum members can join in here and advise me what i'm looking at with these bearings.

i've got so many of these units, it would be a shame not to use them.
i think they would be perfect for use as an z-axis for a light weight dremel type cnc unit.