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CB, I am also blade shopping so I was glad to see this post pop up. It is very confusing with all the different types. I shot an e-mail to Marc TheWoodWhisperer for his opinion (see below). I've learned alot from his website and think he gives an unbias opinion and keeps it simple (K.I.S.S.) which is a plus for me. Pat
Hey Pat. Like most things in woodworking, too many options can simply muddy the water and do more harm than good in terms of confusion. So let's simplify. More teeth equates to a smoother cut with less tearout. Less teeth equates to a more aggressive cut with potentially more tearout. Having less teeth means less heat buildup and more room between teeth for exiting sawdust.
So a dedicated ripping blade should have a relatively low tooth number, because most rips are physically long and they are in the same direction as the grain. So tearout is kept to a minimum. Cross-cuts, on the other hand, are usually shorter in duration and because you are cutting across the grain, they are more likely to tearout. So we like a higher tooth number for cross-cuts. Mitersaws, for instance, usually do best with a higher tooth number since every cut is a cross cut. But if you use a cross-cut blade (like an 80-tooth) for ripping operations, you are likely to have lots of burning and a tougher time pushing the wood through the blade. This will severely shorten the life of the blade. And likewise, using a ripping blade on cross-cutts isn't exactly a good idea either. The cut will be fast and easy, but you'll have a rougher cut and a good deal of tearout to contend with.
Now in most shops, we have one other issue to consider, and that is plywood. We always want a smooth crisp edge, and a cross-cut blade with a high tooth count will do that for you.
So ideally, you would have both a ripping and a cross-cut blade in your shop. But if you ask me, its a real pain in the butt switching back and forth from one blade to another. I am just too lazy for that. So what I opt for is a combination blade (usually 40-50 tooth). A high quality combo blade is capable of giving you excellent results in both rips and crosscuts. Is it as good as using high quality separate blades? No. But for the convenience and savings in time, I will deal with what little tearout I experience, if any at all. And after about 5 years of working with a Forrest WWII, I can honestly say I have never once thought, "Boy that cut would have better with an 80 tooth blade."
Is it capable of producing finish-ready cuts? Well, in my opinion, no. The cut might be super smooth on its best day, but I will always prep my materials by hand before finishing. So mill marks never really bother me.
So as a general summary, 30tooth and below for rips, 40-50 tooth for combo, and 60tooth plus for cross-cuts. My favorite? A 40T Forrest WWII.
Hope that helps!
Oh and by the way, if you want to try a blade that actually does produce nicely sanded edges, check out the Final Cut blade. I am reviewing it as we speak. http://www.finalcutblade.com/
Take care and good luck.
Marc J. Spagnuolo