Simplify setting up your stackable dado by using an easy to make Dado Gauge.
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
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.