Workshop Mishaps: Bits that bite

The Story

Bits that bite

I was building rustic clocks for Christmas presents out of logs that were sawn in half but still about 4" thick. While routing mortises for the battery-powered clock movements I ran into a problem. I had cut as deeply as I could with the only straight bit I had, but there was still too much wood left between the face of the clock and the bottom of my mortise. I had to cut deeper if the clock mechanism was going to reach through to the face of the clock. At that point, I came up with an idea that I thought was genius! Why not use a drill bit in my router? After all, I had a 1/2"-diameter bit with a 1/4" shank, a perfect fit for my router’s 1/4" collet. I chucked in the drill bit and lowered it into the mortise, having the presence of mind to keep my head well above the tool. Moments after flicking the switch, the bit snapped off, ricocheted around in the mortise, then bounced out and hit me squarely in the stomach! (Lucky for me, I had a little extra padding to cushion the blow.) The sharp end of the bit cut me and later left a bruise, but I realize that it could have been much worse. I still bear a faint lightning-bolt shaped scar as an emblem of my workshop mishap.

The Victim

Woodworking has been a lifelong hobby for 45-year-old David Sams of Penrose, North Carolina. At 13 he was helping his family build custom homes. Today, he’s a water treatment operator who spends his spare time building upscale rustic furniture for clients and the vacation cabins he renovates for rental. He also turns pieces sold in local craft shops, using primarily crotches and burls harvested from apple trees whose useful fruit life is over.

Case Analysis

David was young at the time and new to woodworking. In a hurry, he elected to use a tool for a purpose it was never designed for. Big mistake! He was fortunate to walk away with just a minor injury. A router’s 22000 rpm can create a tremendous amount of centrifugal force. For a  1/2" bit that’s designed to run at under 3000 rpm it’s enough to instantly bend and break the shank.

Shop-Smart Strategies

David instantly knew what he had done wrong. If he had taken his time and thought the process through, he might have seen the error of his ways. We checked with Bill Hylton, author of Woodworking with the Router (Woodcraft #147290, $19.95). He provided the following tips:

• First and foremost, only use “router” bits in your router. ’Nough said.

• Read your router’s manual for the dos and don’ts. Here you’ll find warnings for improper use and common sense practices.   

• Never stress a bit or router. Take only 1/8"-  to 1/4"-deep cuts at a time.

• When using large-diameter bits (2" or more), downshift your router from 22000 rpm to a safer 12000-14000 rpm.

• Use the shortest bit that will make the cut. Excessive length amplifies vibration and deflection.

• Don’t hyper-extend a bit. Insert the shank as far in to the collet as it will go, then back it out by 1/16" to ensure that it’s firmly seated.

• Choose bits having the largest diameter shank—1/2" instead of 1/4".

• Check the shank after each use for burrs or rough spots. If you find any, sand them smooth with emery cloth.

• Stick with top-shelf, brand-name bits. Beware of deals offering a rash of unfamiliar-name bits at huge savings. Often the fit and finish of these bits rat out these imposters.

• Always use the correct collet for your router; avoid using sleeves or bushings to make a 1/4" shank fit in a 1/2" collet.

• If your bit vibrates and chatters when you make a cut, it’s probably out of balance. Remove the bit and see if you can return it. 

• Each time you fit a bearing-piloted bit in your router, give the bearing a spin. It should move freely, and its rim should be smooth and free of dirt or grit.

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