The new CMT Tenon-Cutting Router Bit, $99, simplifies making tenons. Working like a massive tongue cutter, CMT's bit cuts tenons from 3/16 in. to 3/8 in. thick and as long as 1-1/16-in. in a single pass. It can handle material up to 1-3/8 in. thick. The bit consists of four stackable slot cutters and an assortment of spacers and shims. The beauty of this system is that once the slot cutters are correctly spaced, every tenon you cut is exactly the same size, regardless of minor differences in material thickness. In contrast, tenon-cutting techniques that require machining one face, then flipping the board to cut the other face, may result in irregularly sized tenons. A guide sheet is included with the bit, indicating which shims and spacers to use to achieve a tenon of a given size, but test cuts are still recommended to perfectly match the tenon to a mortise. You'll need at least a 2-1/4-hp router to rout the longest tenons in a single pass. You also need variable speed, since this bit should run at 12,000 rpm. The shop-made sled (see photo, left) is a must when cutting narrow rails.
CMT, (888) 268-2487, www.cmtusa.com Tenon-cutting router bit, #800.627.11, $99.