TS Cutting not quite flat bottoms

snipped-for-privacy@ganssle.com wrote: | Folks, | | I'm cutting a double tenon on the TS, with about 0.17 between | tenons. Using a shop-made tenon jig to cut the space between the | tenons I wind up with an inverted V shape on the bottom, sticking | up maybe 0.010" (that's a guestimate). | | Tried two blades: a Freud 80 toother, and a Freud 50 tooth | combination blade. | | Any ideas why this wouldn't be flat? The 80 tooth blade is only a | year old and hasn't seen too much wood.

I'm not familiar with those two blades; but most are ATB (alternate tooth bevel). Take a really close look at the blades and you'll see that the teeth aren't flat on top.

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA

I believe that would be because your blades are Alternate top bevel blades. To get a flat bottom you will need a blade with a flaat topl tooth grind.

Examine the blade closely and you should find that there are no flat teeth, they are set to either the left or to the right--this is called an "Alternate Top Bevel" grind and it is the most commonly encountered.

Not a function of the age or sharpness of the blade, but of the design.

If you need a flat bottom you need a special grind on the blade. Forrest has custom grinds on the Woodworker II blade for various purposes--. The WW10401125 is probably what you need but you may want to call them and explain what you are trying to do and ask for a recommendation.

You can't get there from here with either of those blades (I have both of them), time to add the Freud dado set to your arsenal if you want a flat bottom.

Lew

Others have identified the cause of your problem and a couple have provided some not so inexpensive solutions. If it were me I'd just use a file on edge to scrape the ridge from between the tenons, or use a chisel to lower the bridge between the mortises till it clears the tenon ridge.

Art

What about using a rip blade? Don't those have flat teeth?

And there are ATBR blades out there (ATBRaker).