Review on Iverntech MGN12H Linear Rail Guide With Stainless Steel Carriage Blocks - 700Mm Length For 3D Printer And CNC Machine by Dan Germain

Bought of few of these for a 3D printer upgrade and some were pretty rough, but I did not want to quit on these rails. So here a few things I learned from looking online forum boards and youtube videos.1. Clean everything, that includes getting rid of the grease/lube that's already on it, then getting whatever you feel comfortable to grease/lube the parts.2. Inspect the Carriage block, sometimes changing the small ball bearings help or sanding extremely lightly the excess plastic guide to keep the paperclip like bar straight enough to hold the ball bearings.3. Inspect the Rail where the ball bearings make contact. The rail may be off like micrometers or smaller than micrometers making it feel as the carriage needs more pressure to move it. There can also be hairline nicks here and there causing the carriage to catch in certain areas. You can take out a bearing and lightly rub it on the groove so you can feel the hairlines. To remedy the bad rails, carefully and patiently use a fine wet whetstone edge to smooth/sharpen the groove evenly. Don't over do it to the point the carriage begins to wobble.4. Just give up or return the product or buy another and pray for a good lottery.I would recommend working on these to get them working again, it doesn't hurt to learn how these work if your building your own 3D printer, CNC, laser machine, etc.