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 Home > Joinery Techniques > Dado Gauge

(Mike Krivit)

(Mike Krivit)
Photo 1

(Mike Krivit)
Photo 2

(Mike Krivit)
Photo 3

By George Vondriska

So, just how thick is 3/4-in. plywood? It's always a little less than 3/4-in., but exactly how much less varies from sheet to sheet. The sheet-to-sheet variation makes setting up dadoes tricky, and can lead to lots of trial and error cuts. You can virtually eliminate trial and error dado cuts by making a simple Dado Gauge, see Photo 1.

The gauge consists of a series of dadoes ranging in size from 23/32-in. to just over 3/4-in. Starting at 23/32-in., each dado increases in width by .005-in. Make these incrementally bigger cuts by adding dado shims to the stack. Dado shims as tiny as .002-in. are available, but I've found that .005-in. increments work fine for the gauge. It's best to make your Dado Gauge from plywood so it's not subject to seasonal expansion and contraction.

The largest dado on the gauge is 3/4-in. plus .010-in., so I can use the gauge on melamine, which tends to run over 3/4-in. thick. Once the dadoes are machined, record the dado's width in the bottom of the cut. I used a label maker, but hand written dimensions would be fine.

Use the Dado Gauge by testing a piece of your project plywood in each dado until you find a good fit, see Photo 2. You've got a good fit when the piece slips in with hand pressure (you shouldn't have to drive it in with a mallet) but there's enough friction in the dado to grip the plywood.

Once you've determined the correct combination of dado blades and shims, build the stackable dado up to this size, see Photo 3. Make a test cut and check the fit. If your set of dado shims includes shims smaller than .005-in., you can tweak the dado width for an even better fit, if necessary.