(03-16-2012, 09:58 PM)Tony Wells Wrote: Cut the original slot, like PixMan said, but go about 0.010/0.015 deeper than the "bottom" of the tee slot will be.
+1 to that!
It helps so much with the cutting action when the center of the T-slot cutter isn't in contact with the bottom of the slot you cut.
You might want more width clearance than just .005". If you look at the chart for cutters from those suppliers, you might notice that they are suggesting at least 1/64" (.015") over the bolt size as the slot width. Looks like the cutter "neck" diameters run 1/64th over nominal, so you should make the clearance slot width a little more than that.