For many, many years there has been a long-held belief that Zero Clearance Table Saw Throat Plates give better quality cuts on the underside of the material being cut than non-zero clearance throat plates, and I too, have been a perpetrator of this theory. Many Years ago, before carbide tipped tables became popular and we were still using steel blades, I tested this theory and ... yes, zero clearance inserts did improve the cut.
For some reason, lately, I wondered that with the much better quality of saw blades if this theory is still true or not so I decided to try out a few of the blades I have and see if do cut better with zero clearance or not.
Watch it on Youtube: https://www.youtube.com/embed/h7PpHpZyhKA
I started off by trying some of my crosscut blades on some very dry, fine grain fir. I Set up my table saw first with a Freud 90 tooth cross cut blade and with the zero clearance insert I had made and made my first cut .. they replace the zero clearance insert with the factory non-zero clearance insert and made the second cut ...
... I carried on with this methodology with the Freud 60 tooth crosscut, the Freud 50 tooth Combination blade, and finally with no-name 40 tooth combination blade. I decided that the results of the test were very hard to see if there was any difference between the zero clearance and non zero clearance when using wood, so opted to use double sided Melamine which is a much better indicator or cut quality. 
Here are the results of the crosscut and ripping test using wood. Can you see a difference???
Cross Cut Top Side Cut
Cross Cut Bottom Side Cut
Ripping Cut Top Side Cut
Ripping Cut Bottom Side Cut
Melamine Top Side Cut - Cross Cut AND Ripping Blades
Melamine Bottom Side Cut - Cross Cut AND Ripping Blades
Close up of above
Blade Selection - These are all the blades I tested
Right to left - Freud 90 tooth thin kerf, Freud 60 tooth thin kerf, Freud 50 tooth Combination thin kerf, No Name 40 Tooth Combination Blade, Freud 24 Tooth Ripping Blade thin kerf and last Freud 30 Tooth Ripping Blade full kerf.
Conclusion
As you can see from all these test results, there is little or no difference between cuts made with zero clearance and non-zero clearance blades that I tested. Other blades and other materials may give different results than these and the only real way of telling whether your blades and your woodcuts make a difference is to make your own zero clearance inserts and compare them with your saw blades to see if they make any difference. For me, I'm satisfied that for all the blades I use, making zero clearance inserts is pretty much a waste of time for little if any gain ... but that's technology of blades, always getting better and giving us better quality cuts with less effort.
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Copyright Colin Knecht
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