Is it safe to use 71⁄4" circular-saw blades stacked together for making dadoes on a tablesaw?

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Q:

Is it safe to use 714 " circular-saw blades stacked together for making dadoes on a tablesaw? Each blade is about 18 " thick. I get tiny ridges, but clean them up with a chisel. Also, I have a wobble dado blade that I can use on either my tablesaw with a guard on or on my radial-arm saw without a guard. Which is safer?
—Les Willoughby, West Valley, Utah

A:

You can use stacked circular-saw blades to cut dadoes on a tablesaw, Les, as we confirmed in the WOOD® magazine shop, but your dado cut quality will suffer. To make circular-saw blades cut even rough dadoes, you'll need blades of the same brand and model to avoid minor differences in diameter. We checked two brands of blades and both had teeth between 116 " and 332 " wide, not 18 ". So three new blades costing about $10 apiece would only make a dado less than 14 " wide, as shown above left. That's with two cardboard spacers on both sides of the center blade.

Stack enough blades to make a 34 " dado and you've spent more than the price of a Freud SD206 6" dado set that will produce flat-bottom cuts with greater adjustability and better chip removal. By cutting cleaner, a dado set lets you eliminate the cleanup stage using your chisels.

Circular-saw blades leave uneven dado bottoms, as shown above right, because the teeth on many types have alternating top bevels for faster cutting, as illustrated below. By comparison, the tops of dado-blade teeth are ground to produce flat-bottom cuts.

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Alternating top bevel teeth

As for that wobble dado, Les, we've never been a fan of these either on a tablesaw or radial-arm saw. Stacked dadoes produce cleaner cuts and work quieter than wobbles.

Whatever your choice, safety dictates that you use your tablesaw unless you're able to fit your radial-arm saw with a dado-blade guard. Two other reasons to use a tablesaw: You're protected from most of the blade and you can use both hands to control the speed of your cut.