I use a flush-trim bit a lot, particularly for trimming face frames to cabinet sides and parts flush with templates. Unfortunately, after a few sharpenings, it's not a flush-trim bit any more. It's an almost-flush-trim bit, because of the cutter's reduced diameter. CMT's new carbide insert bits, $85, solve this problem, plus a few others. “Whoa!” you say. “85 bucks for a flush-trim bit?” You're right; it's a lot of dough. A comparable noninsert flush-trim bit with a 1/2-in. shank and 1-in. cut length costs around $35. But let's do a little math. The carbide inserts are double-edged, so you automatically get two bits for the price of one. That eliminates one $10 sharpening. After you've worn out the second edge, replacement cutters are only $6 per pair, which is like getting two flush-trim bits, because they're double-edged. So the inexpensive replacement knives save you another $20 worth of sharpening. Finally, the carbide used on CMT's insert cutters, as on almost all insert cutters, is higher quality than on noninsert cutters, so it lasts longer. Insert router bits aren't for everyone. They're obviously more expensive than their noninsert counterparts. But if you're a heavy user of router bits, especially if you do lots of work in abrasive material, such as particleboard, MDF or plastic laminate, they pay off in no time.
CMT, (888) 268-2487, www.cmtusa.com, Double Flute flush-trim bit, 657.692.11, $85, Replacement knives, 790.300.300, $6.