I used 3/4″ aluminum angle stock from Home Depot. It is important to drill holes off-center, closer to the corner of the L.
Click the image for a larger view. (Note: You may want to stagger the holes so the bolts do not bump into each other when assembled. I was lucky and my bolts just missed each other)
I got clever and did my first set of brackets with the holes centered on the side of the bracket – and it didn’t work. You can see from the photo that the two angle brackets hit each other. Too bad I made all 4 brackets before I tried them out.
The holes are drilled and tapped. I used bearings from VXB Bearings.com (www.vxb.com/). The price was great, less than $4.00 for 8 bearings. Delivery was very quick. Article number sk8zz – 8 Skateboard Bearings 608Z Shielded.
Be sure to either use a template or a drill press to get the holes placed as accurately as possible. This way the bearings will ride evenly on the track. You’ll need to make 4 of these.
Drill the holes at 17/64" and tap 5/16-18. A 5/16" bolt has a diameter of .3125" and the inside diameter of the sk8zz bearings is .3150" (8mm) - a very nice fit. Attach the bearings with a 5/16-18 x 3/4" bolt, capturing the bearing between a nut and the bolt head. No washer is used.
The 8 inch X axis linear slide bearings are identical in design except they are, you guessed it, 8 inches long.
Here's how the finished bracket rides on the opposing rail.
All bearings contact nicely and the two angle brackets are now nicely separated.