VEVOR Linear Rail Slide SBR20-1200mm 2 PCS and 4 PCS SBR20UU Slide Blocks Linear Guide Rail and Bearings Kit for Automated Machines DIY Project CNC Router Machines

I used these to upgrade my slab flattening jig. It used to have small aluminum rails that rocked back and forth when you moved it across the slab. These things are rigid and don't wiggle at all.

VERY smooth and true, I will be buying the 4000mm version soon

These rails are very nice for the money would recommend to anyone.

A straight edge laid across the bar shows a deviation of about 1/8 of an inch end to end. I was going to use these for a planer sled as others have done but with the bow in the rail you would get a board thicker in the middle than on the sides. 1/8 " would be a lot of sanding to make the board flat. My old mdf sled which cost next to nothing is a lot flatter. Also the aluminum ends are very roughly cut and protrude out from the round bars, so would have to be filed off if you wanted to put two of these end to end for the table part of a router flattening jig. One of the bearings had some play on the bar but the set screws on the block adjusted the tightness. Update: Contacted Vevor support - extremely helpful and very responsive. Found out that because the difference in the thermal coefficient of expansion between aluminum and steel the bars will distort as the temperature changes ( AL is 2x or more than steel you can visually check this by using a long straight edge and warming the bar/aluminum combo with a hair dryer). They had me loosen the bars from the aluminum and check them again - the distorted one was still distorted even if I removed the aluminum entirely. I sent a picture and Vevor sent me a new bar and it is straight as it should be. Five stars for support, 1 star deduction for sending a bad bar to begin with. For those that are building a cross flattening sled - I was trying to decide whether to use just the bars or the bars with the aluminum extrusion, not knowing how much sag the bars would have with the router and it's carriage. With the aluminum there is no detectable sag, so if you are in a temperature controlled environment then if you loosen and then tighten the bars on the extrusion it will not sag with a router. If, however, you have limited room like I do and setup your flattening system outside then the temperature extremes as far as I can tell could make the bar flex by .5 to 1 mm (depends on what the temperature is and what the temperature was when the bars were tightened). Testing with just the 2 bars ( no aluminum) at full span with a 12lb weight in the middle then the weight appears to make it sag by about .3 mm. Temperature will not affect it. This is with 2 1200mm long, 20mm dia. bars. If the distance is shorter the sag will be less and if the bar diameter is smaller the sag will be more. Obviously if the router/carriage weight is less it will sag less. I am planning on making my sled with just the bars (which would have been cheaper had I known this ahead of time).

Smooth bearings. Nice finish. Works great. would buy again.

I am very happy with this vendor. In the past I have made 4 different orders with other vendors for this product only to receive them damaged. Finally got a clean set.

The product i received was obviously a return. The tape on all the packaging was cut and the hardware was in a gallon Ziplock brand bag. Also marking and blemishes from use on the rails. But other than that I can't find anything wrong with the product

Perfectos