Review on Iverntech MGN12 400Mm Linear Rail Guide Upgrade For Ender 3, Corexy, Tronxy, Delta Kossel 3D Printers And CNC Machines With Stainless Steel Carriage Block by Ognjen Cao

I ordered a total of 4 rails from this vendor, so far I've inspected 3 and out of 3, One of them is completely unusable, first it appears to be short a few ball bearings and The cart is extremely rough when moved by hand, the cart also won't fall under its own weight.Upon closer inspection I can see what appears to be rust in the bolt holes and the carriage or cart looks discolored as does the rail.I don't understand why the carriage appears discolored it's almost as though there's corrosion on it and they claim this carriage is made out of stainless steel so there shouldn't be any corrosion even if exposed to salt air.So all I can conclude is Either The package wasn't airtight and leaked on the way over from China which causes develop Russian corrosion or it's a customer return either way it's completely unusable.When tilted The carriage should fall under its own weight, two of these do this and are relatively smooth.Out of three carriages one of them is pristine, I would rate 5 stars, The second one I would rate a 3.5 stars, It's perfectly usable but not nearly As good as the first one.The third is completely unusable, When moved by hand the cart is very rough and gritty and it takes considerable force to move the cart, almost as though it's on the wrong rail or they have the wrong size ball bearings in it. I even tried putting a couple drops of sewing machine oil on the bearings to see if that would help but it was a complete waste of time.So out of three rails I received one that I'm very happy with, one that will work but I'm not overly thrilled with and one that was DOA.This is the second This week I had to return linear rails, I had purchased two others from another vendor, while they weren't as bad as the worst one in this set they were still very rough and unusual.It would appear as though buying linear rails on revain is really a hit or miss proposition, So far my experience has been about a 30% defect rate on linear rails. And it's not like my standards are extremely high they just need to move smoothly and fall under their own weight. If I have to bang the thing on the table to get the cart to move then there's no way it should have passed quality control.Now I'm not sure if the vendor inspects these when he receives his order because I would assume if he did they would have caught the rust on the linear rail with a leaking packaging.This particular company came highly recommended, so I'm somewhat surprised. I'd actually return two of these but I don't want to risk damaging my revain account by returning too many products. If it wasn't for that, I would have returned two out of three of these rails.Anyhow this is really annoying I was hoping to finish this project this weekend. Now it probably won't get finished till next weekend so I'm down a week. And that's assuming the replacement rail they send isn't defective as well.