This article was inspired by a question from Steve. He writes:
I have recently embarked on building bookcases and I have run into an issue. I decided to use a cabinet grade birch plywood that I picked up from the hardwood dealer here in Dallas. Everything was fine until I started the cross-cuts and experienced tearout on the top layer of the plywood face. I stopped this by doing all my cuts with a skill saw and plywood blade. But when cutting the dados, I still got quite a bit of tearout. I like using this plywood because its inexpensive. So my question is: how do I stop tear out on plywood?
There are few key things that you can do to prevent tearout in plywood. First, use a zero clearance insert on your tablesaw. A zero clearance insert fully supports the wood fibers right at the cut line, which will dramatically improve your cut quality. You can buy insert blanks specifically made for your saw, or you can just make your own from plywood or MDF.
The second thing you can do is use a high quality, high tooth count blade. I generally use a 40 tooth Forrest Woodworker II or a Tenryu 40-tooth Gold Medal blade, and that works just fine. But if you are still getting tearout, you might try a blade with 60-80 teeth, such as this one from Freud. More teeth equates to a smoother cut and less tearout. You’ll also notice a key element of that particular blade is the Hi ATB (alternating bevel). This means that the teeth on the blade are milled at a high angle for more effective scoring of the plywood, thereby creating less tearout.
Now for the dado blade, it just comes down to sharpness and the properties of your particular dado stack. Some of the more budget-friendly dado sets will give you tearout no matter what you do. But the higher quality dado sets will produce tear out free cuts until they start to become dull, at which point you’ll send them out for sharpening. I use the Forrest Dado King, which I picked up used about 6 years ago. But before that, I used this Freud dado set with great results. In fact, I still think this Freud set is the best balance of price and performance.
Another thing you can do to prevent tearout involves our old friend blue tape. Just run a strip of blue masking tape along the cut line on the side that you anticipate tear out. The tape helps to hold the fibers in place during the cut, and usually the result is a clean crisp line. But with a zero clearance insert and a high quality blade, this step is usually unnecessary.
And the final thing you might try is making a scoring cut (image borrowed from American Woodworker). If you raise the blade about 1/32″ and make a very light initial pass, that will usually cleanly sever the fibers on the face of the plywood. That way, you can make a second pass with the blade extended and you’ll end up with a tearout free cut. A number of larger saws out there are actually outfitted with a second blade that lives in front of the main blade, and its sole purpose is to make this type of scoring cut.