How To Shim Drawer Slides

I just built and installed four drawers into a bed frame I recently built. I was careful to keep everything square and parallel and the finished sides of the drawers as well as the cabinet where they go are parallel to better than 1/32 inch (0.8 mm).

To avoid headaches, I made the cabinet openings about 1/8 inch (3.2 mm) wider than the drawers plus the one inch required by the slides (1/2 inch each side; total cabinet opening is 1 + 1/8 inch wider than the drawer).

However, not one of the drawers slides easily. They feel like they are binding and scraping wood against wood. I have looked carefully and am certain the drawer bottoms, tops, sides, and edges are not touching the cabinet at any point along the way.

I used these soft closing ball bearing slides:

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I think it is the rails themselves that are scraping the drawer and cabinet. Looking down them, along the sides of the drawers it looks pretty tight: enter image description here

That is the left drawer edge (with dovetails) at the left and another drawer at the right. The parallel plywood is the center support and "cabinet edges" for both drawers. The extra 1/8 inch width is made up by using the slide's "shim tabs" (for lack of a known name) which is being used on the left slide in the photo. The right drawer's right slide (not in photo) is doing the same thing for the right drawer.

I see there is an answer for how to install slides so they line up and work properly, but after reviewing it, I think I covered it as best I can. That answer's links talk about leveling, for which I installed the slides by measuring the same distance from the top of the sides which are level which support the plywood under the mattress. I had squareness in mind at all aspects of building. I couldn't make much sense of this one and this is all about the special jigs sold.

Naturally the instructions that come with the rails are useless: Install the rails as required (or something to that effect).

So, what am I overlooking? How should the slides be installed to work smoothly and without scraping?