How do I keep router bits from slipping in the collet?

While table-routing ¹⁄₄ " grooves in drawer sides, my bit changed depth during the cut. That, of course, created uneven grooves. I retightened the bit into the collet as much as I could, but it slipped again. What am I doing wrong?
—Greg Summers, Erlanger, Ky.

Router-bit slippage is both frustrating and dangerous, Greg, and usually results from dirt, damage, or both. Built-up dust, pitch, or other debris on the bit shank or router collet compromises the collet's grip. Give your bit's shank a quick cleaning with mineral spirits or lacquer thinner and a nonscratch scouring pad, as shown above. Next, clean the collet by blowing it out with compressed air, and then lightly sand its interior with a dowel wrapped in 600-grit abrasive. Inspect both the bit and collet for any damage. If you find any, invest in a replacement rather than using the faulty one.

Send your woodworking questions to askwood@woodmagazine.comEven a clean, well-maintained bit can slip if installed improperly. Never bottom out a bit in the collet; instead, raise it about ¹⁄₈ " from full depth before tightening the collet nut. And no need for white-knuckle tightening; you only need to snug the collet nut firmly.