UniTak3D Ender 3 MGN12 Linear Guide Rail 400mm with MGN12H Bearing Steel Carriage Block for Anycubic Ender 3 CoryXY DIY 3D Printer and CNC Machines

Upgraded by core XY 3D printer to linear rails. All ran super smoothly across the length with no effort. No factory crap to remove and no added oil required.Rails were extremely straight and the added bumpers were a nice addition. Packaging was above standard and the black finishes were a great, classy touch. If you're looking for #12 linear rails, these are the ones.

I got this rail for a camera macro focusing rack and I'm pretty happy with it for the price.Much like all low-cost linear rails, these come with the same caveats: The metal parts will have a thin film of grease from factory, and the bearing itself may bind up slightly due to factory grease. The actual hardware is good, however, and with about 20 minutes of your time and a few dollars they can be transformed into great performers: Remove the rubber endstops, remove the carriage, clean everything with isopropyl alcohol to remove old grease and pack the bearing with new grease (I used synthetic PTFE "super lube").Once slightly loaded the bearing runs as smooth as can be. You may consider replacing the ball bearings with new precision ball bearings, but I did not find that to be required.For those interested, the rail itself is 12mm wide, and the carriage is tapped with an M3-0.5 thread.

When these arrived I broke the block down to clean everything. Internally they look the same as all the other linear bearings. Had quite a bit of brown/yellow fluid inside. I imagine for shipping purposes. Once they were reassembled and lubricated I put them back on the clean rail. They are smooth but boy are they tight. I usually test by placing the rail vertical and seeing if they will slide with gravity. These didn’t even attempt to move. There wasn’t any binding at all. Even after cycling back and forth dozens of times, I didn’t notice any better results. 4 stars because they are smooth but not 5 because they are super tight.

This rail looks and works great right out of the box. It is super smooth and isn't covered by dirty grease requiring extensive cleaning like many other non-Iwinn rails available.I was planning on changing out the bearings once I got it to high quality bearings, but I don't think I need to. I installed this on one of my ender clone 3d printers on the x axis to replace the v slot gantry and it's so much more reliable now. I'll get more of these to do the y and z axis next. Highly recommended!

This linear bearing is really nice because it is actually all black which I like even my hidden work to be uniform and it looks super clean. The bearings are very high quality, just clean and grease them as other comments say, and this thing will be perfect for a very long time.

ordered 2 for my new 3d printer. the packaging is very good. each rail is vacuum packed. a thin layer of grease on the rails. need to wash off with alcohol and grind with a high-quality lubricant. rails slide smoothly with no play. i will order couple more rails.

I was pretty excited to receive the linear rail today. However, after opening the package, the sliding action is far from smooth. At certain spots on the rail it feels like it is binding pretty hardcore. I'm sure it will self clearance after repeated use. But, it's supposed to be precision. I'm still going to add some grease and give it a try. If it gets better, I will update my review.

The rail and block are smooth and quiet with no free play. I will be buying more for sure.