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:
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:
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?
Best Answer
1/16" is going to make a difference here. Very small margins.
Don't rely on those metal flaps as shims. If you need shims, use shims.
You have not done anything wrong, you've just entered the PITA adjustment phase. Higher-quality hardware has adjustments which can be made after the hardware is installed. These slides are not that. You are fortunate that your problem is the width and not vertical because you'd hate to have to move the glide 1/16" up or down - the screw would keep getting sucked into the old hole.
Take it apart and flatten out those "shims." Then put it back together and try it. Based on the math, it won't be quite right. Add 1/16" shims to both sides and try that. If you have measured correctly this far, you'll be done. Obviously if it doesn't work, try 1/16" shim on only one side. Get some serious shim material that you can measure and which won't compress. And whatever you do, don't strip the holes with all of the in and out.
Whatever that other answer said about support in the front does not apply. These glides don't need support. If they require support it's not done properly.