Linear guide resistance...

[SatanKlawz]

I am putting together my machine and I have the x axis rails and bearings installed. They are HIWIN LG series 20mm rails and blocks. The bearings that I bought have a p/n designation that says they have a "light preload". I have 2 on each side of the machine for a total of 4. When I move them back and fourth by hand there is a noticable amount of resistance. Not a ton but a decent amount. They run smooth but are just stiff. Will these wear in and be easier to move or should I have bought the non preload version? My machine will be moved by steppers and I am wondering if this will affect the machine in any way?

[hemsworthlad]

Hi,
No this is quite normal so long has it's not too excessive and is even all along the rails length.
If you give them an average push they should slide for a short distance the stop gently IE not in a harsh abrupt gerky stop.

They will free off slightly under use but not too much, they will feel smoother when they have weight on them as well.

My rails did this also and it worried me too.!!. . . . But worrie not.

[louieatienza]

hemsworthlad hit on something that I found out tuning my x axis - the key is having an even feel thoughout. Definitely don't want it tight, then free, then tight or such. Between the steppers and leadscrews, they can output a lot of force, more than one may realize....

[SatanKlawz]

The resistance is even along the rail. However you can not just give it an average shove and have it coast for a bit, it will stop almost immediately. There seems to be a little bit more resistance than what I was expecting but at the same time it does not feel excessive or like something is in a bind. Its feels almost like there is a set screw that adjust the tension that is set just a tiny bit too tight.

[CarbonKevin]

I wonder if the rails were coated with some sort of heavy grease to keep them from rusting? That would certainly slow up your movement. Give that a good wipe with some solvent on a rag...wear gloves and a respirator, though!

[SatanKlawz]

Yeah they do have a super heavy coat of grease on them. Its not real thick but it is there.

[hemsworthlad]

Yes this may be causing it, do what CK says and clean it off but only the rails the bearings obviously need to be greased.

I think you'll find they will be fine and so long as there is no obvious binding or sticking then you wont have a problem.
When i say a short distance i do mean only 6 or 8 inch and not 2-3 feet.!!

I,ve just been and tested some rails that i have here for another project, not hi-win but equivelents and if i line the end of the bearing with a hole on the rail and flick the bearing hard with my index finger on the edge thats lined with the hole then it travels between 3 and 4 holes the holes have 60mm centers.

Hope this helps.

[madtownrob]

Same issue here. I ordered the LG "light" preload because the light and very-light were said to be negligible in the felt difference. I went from V-rail and bearings to LG 20 series and you just can't push the blocks and have them move freely. I have tried to clean the rail and it feels better than it was, however still no free movement.

[hemsworthlad]

Originally Posted by madtownrob Same issue here. I ordered the LG "light" preload because the light and very-light were said to be negligible in the felt difference. I went from V-rail and bearings to LG 20 series and you just can't push the blocks and have them move freely. I have tried to clean the rail and it feels better than it was, however still no free movement.

You'll be surpised just how free they slide when you have the full weight of the gantry etc mounted onto them.!!

If they are still very stiff when the gantry etc is attached then i would be concerned and start looking to see if the rails are mounted correctly and straight, it doesn't take much missalignment to cause them to bhind.

[SatanKlawz]

There is no pushing or flicking them and having them coast ANY period. I am glad someone else noticed. The rails are mounted but even with no gantry pieces installed and nothing to even try and make it rack or bind the result is the same. I have 6 of these blocks and all 6 feel the exact same.

[stef_d]

Originally Posted by SatanKlawz There is no pushing or flicking them and having them coast ANY period. I am glad someone else noticed. The rails are mounted but even with no gantry pieces installed and nothing to even try and make it rack or bind the result is the same. I have 6 of these blocks and all 6 feel the exact same.

I also have some hiwin equivalent, they look pretty decent quality.
and they are also stiff. they wont coast either.
i have yet to properly test if this is an issue or not, as the gantry is not in place yet. They are much stiffer than i would have anticipated, but then again, it's the first time i used such rails, so beware of preconceived ideas !
It may all be completely normal.
try this test maybe: hang the rails vertically, and hook up some weigths on the carriage until it starts moving from gravity only.
then tell us how much weight that was.
knowing your stepper torque will tell you if you are miles out, and if they are indeed too stiff.

[SatanKlawz]

These rails and blocks are rated for some prety serious loads. I get the feeling that this is normal for a block that can handle such a high load and stay true to its linear path. I do not think its a deal killer at all it was just more than I expected.