Dealing With Drawer Slides

In my recent second post about my new rolling drill press table (link), I stated that there would be a part three, in which I added a drawer base to the table. I made the base, but it's just a bit boring and straightforward to actually write about. But during that process, I decided that I would figure out once and for all how to space drawer slides without a lot of trial and error. This photo from the rolling cart (link) for small parts and fasteners that I made for Make717 will show the issues involved:

The numbers I added show four different spacings I needed to know for this cabinet, which used only two different drawer sizes:

1. case bottom to first slide.

2. space between two large drawers.

3. space from a large drawer to a small drawer.

4. space between two small drawers.

If those had been regular wooden drawers, there would have been a fifth spacer to set the height of the inner part of the drawer slide on the drawer itself. In practice, I cut each of those spacers on the table saw out of scrap (Masonite works great), and use them to install the slides from bottom to top. When making the cabinet above, I installed the inner and outer slides on the bases, stacked them up with scrap spacers between, and carefully measured with a digital caliper to determine the spacer sizes. It worked fine, but pretty crude and time-consuming.

In industry, all the measurements are done from the mounting holes for the drawer slides instead of the outside surfaces of the slide, and most factory cabinets are made to a European standard where everything is done in multiples of 32 millimeters. That doesn't really help in a home shop, because I'm not using computer controlled tools to drill the holes. I'd still need spacers, ones which also included bushings to precisely drill the holes. It's easier to just use the drawer slide itself to space the holes.

Another big problem is that drawer slides change in dimensions too, based on length and on the drawer's weight capacity. The process has to start with careful measurements of the slides for each project. That's where I started, with this sketch made in the shop:

As you can see, the measurements of the inner and outer parts of the slide are not anything that's useful for easy calculations, although this particular slide has the interesting characteristic that its overall height as a fraction is 11/8", with an 11/16" inner slide leaving 11/32" gaps on each side. Probably just a coincidence.

When I drew that, I was thinking I'd use the same spacing (1/2") from the bottom of the drawer to the inner slide, and the bottom of the case to the first outer slide. However, that leaves a different gap at the bottom of the first (lowest) drawer than the gaps between drawers. Looks weird. 

I brought my measurements home and made a few drawing, just trying to figure out an easy formula. There's not one. In the words of Mark Watney, the protagonist in The Martian, "I'm going to have to science the (expletive deleted) out of this!" I started making a spreadsheet to do the calculations, and in the course of my attempts, came up with a solution that I'll use forever. First, you enter some initial variables:

Total Slide Height: the measured height. 1 + 3/8" in the drawing above.

Inner Slide Height: again, the measure height. 11/16" in the drawing.

Then, you specify two things you just decide:

Drawer bottom to bottom of inner slide: make it something easy to make, like 3/4" or 1".

Gap between drawers: whatever you like.

Then, you can enter the dimensions for each drawer, starting at the bottom, up to 10 drawers. The spreadsheet computes the height of each spacer for installing the outer slides, and computes minimum drawer height and the inner cabinet dimension - very useful for playing around! I also figured out how to display the spacers and heights in inches and fractions, which is how woodworkers usually roll.

Once I had it all working, I designed a "blue sky" cabinet for this post. Those drawer slides from eBay come in packs of 20. I made a plan for a 20-drawer tool cabinet with three drawers across. The eight outer drawers on each side are shallow, and there are four deeper drawers in the center. Here's a crude sketch:

A rolling base like this with drawers 18" wide would be a total of 60" wide - a useful tool cabinet. I may make one someday. For now, here are screen captures of the spreadsheet output for the eight outer drawers, followed by the four inner drawers. You'll probably want to click the images to blow them up so you can read them.

In doing those calcs, I designed the outer part, and then played with dimensions on the four inner drawers until the calculated "inner cab height" matched the first set. You're welcome to the Excel spreadsheet if you want to play with it. Drop me an email at emz3cp@gmail.com.