Rather than fiddle around with shims, I find it easier to adjust a dado set slightly under the exact dado width required, and make two cutting passes.

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Rather than fiddle around with shims, I find it easier to adjust a dado set slightly under the exact dado width required, and make two cutting passes. Or, likewise, use a full-kerf (18 ") blade to cut grooves for 14 " plywood. You just can't beat the fit control that comes with two passes.

To accurately set that second cut without having to make test cuts, I use a dial indicator with magnetic base, (item MMD-100, from Penn Tool Co., 800-526-4956, penntoolco.com). To start, use calipers to measure the thickness of the material going into the dado or groove. Make the first cut slightly narrow. Then, place the magnetic base/dial indicator on your saw's fence rail or table as shown, zero it, and adjust the rip fence to the difference between the first cut and the desired full cut.

It still makes sense to set up an adjustable dado set for full-width cuts when doing production work. But when you just need a dado or two for a small project, this method delivers accuracy, speed, and simplicity!
—Dan Martin, Galena, Ohio