Let a pro do the resharpening, but between trips keep then tuned up with a few file strokes.

Router bits, even those tipped with carbide, dull faster than you might expect. It happens quickly in solid wood, and even more quickly when you work with plywood and other resin-filled sheet goods.

When a dull bit needs regrinding, it's time for a trip to a good sharpening service, which can set you back as much as $10. Only a qualified professional has the machinery and know-how that are necessary to maintain a bit's precise geometry.

However, you can prolong the time between regrindings by lightly honing the bit's flat side with a file every so often. Note that we said lightly, and only on flat surfaces. Don't mess with the bit's hook angles. Even the pros don't do that.

All you need to hone high-speed steel and carbide bits is a pair of diamond honing files. We've found them priced at $6 to $7 apiece in catalogs and at woodworking supply stores.

Start with a fine (600-grit) file and finish off with a super-fine (1,200-grit) version. Work carefully and don't overdo it. Here's how to keep your router bits on the cutting edge.

1. If the bit has a pilot bearing, start by removing it, shown below. If the pilot isn't removable, make sure to keep the files away from it. A slight flat spot ruins a pilot.


2. Next, remove pitch and tar, which can build up in a hurry if you frequently rout softwoods. Apply lacquer thinner or oven cleaner and scrub the bit with an old toothbrush, as shown below.


3. Begin honing with the fine file, as shown below. Count the sharpening strokes or alternate the cutting edges every few strokes to assure that they're honed equally. It's better to do too little honing than too much. You might be surprised by how quickly a diamond file cuts even carbide.


4. Finish off with the super-fine file. Again, apply an equal number of strokes to each of the bit's flat faces and use only moderate pressure.

Lubricate the pilot bearing with light oil, as shown below, and replace it. Also wipe the bit with oil to guard against rust that can pit polished surfaces.


Time to Seek a Pro?

Is it time to seek professional help? You can hone a router bit five or six times, but eventually it needs professional grinding. The following tests will tell you if that time has come.

  • Inspect the bit in good light. Look for nicks or blunt spots on the cutting edge.
  • Hold a fingernail against the cutting edge and gently rotate the bit. It should shave the nail with very little effort.
  • Run the bit through softwood, watch how it cuts, and examine the surface it leaves.
  • Check the chips. If they look more like sawdust than thin shavings, the bit needs professional help.

We visited Puckett Tools' new shop in Waukee, Iowa, to see router bits sharpened on professional equipment. Chris Miller, 22, shown below, uses a Foley-Belsaw machine equipped with a diamond wheel to get the kind of results you see below.


Notice that Chris wears latex-coated gloves to protect his fingers and keep a firm grip on his work. He puts the bit in a chuck, turns a couple of cranks to line it up with the wheel, then works it back and forth with a lever. A couple of minutes, and he's done. The shop charges $5.75 for two-flute bits and $24 for three-wing, raised-panel bits.

Chris says you can have straight bits sharpened many times. Profile bits, however, might need replacement after about four trips to a professional.

These bits from the WOOD. magazine workshop were showing a lot of wear. Chris used a wire wheel to clean off all the residue before taking them over to the diamond-wheel sharpener.