With several recent discussions on stacked dado sets, I frequently see comments about "perfectly flat" or "truly flat" bottoms in regards to the performance of various dado sets. In an effort to be accurate with the claims, I often challenge those claims because AFAIK the vast majority of high quality stacked dado sets like the Forrest Dado King, Infinity Dadonator, Freud, CMT, Amana, Oshlun, DeWalt/Delta, and Systimatic sets all use beveled teeth on the outside cutters to help minimize tearout. In order to be of any benefit, the beveled teeth must protrude slightly above the flat teeth of the inside chippers. The protruding beveled teeth leave tiny grooves at the outside of the cut…a trait often called “bat ears”. The better sets tend to stagger some flat top ground (FTG) teeth in between the beveled teeth to minimize the depth of the bat ears, but they’re still there. It’s minor enough that a lot of people may not even realize they're there, but it’s not realistic when manufacturers or owners claim that these sets leave "truly flat" bottoms, if indeed they don’t. It’s likely that there are sets available that don’t have any beveled teeth on the outside cutters and use all FTG teeth, which will leave a flat bottom, but those sets will also exhibit more tearout, especially across the grain that the better sets that use beveled teeth.
I'd like to hear from owners of stacked dado sets. Please check the teeth on your outside cutters. What set do you have, and does it use any beveled teeth on the outside cutters? Does anyone have a set that uses beveled teeth on the outside cutters that gives a truly flat bottom with no bat ears? Anyone have a set with all FTG teeth on the outside cutters?
Here’s a pic I copied from Forrest’s website that shows the correction orientation of the cutters…it also illustrates the bat ears left by the beveled teeth: