How to Detect Dull Jointer Knives

Most woodworkers put off sharpening their jointer knives as long as possible because sending the knives out to be professionally sharpened and then having to replace the knives in the machine can be a hassle. However, if you notice that your jointer no longer performs as well as it once did, look for any of these four signs indicating your knives no longer are sharp enough to do their job properly.
Step 1Unplug your jointer, then examine the edges of the knives. Can you see them clearly? Shiny edges that reflect light usually are the first indication of dull knives.

Step 2Plug the jointer back in and turn it on. Place a scrap piece of board on the in-feed table, and butt the edge against the fence. Set your push block on top of the board, then use the push block to slowly feed the board completely over the cutter head. Does the board travel smoothly over the cutter head, or does the board lightly vibrate against the table or perhaps stick slightly as you push it? Vibration and sticking also are signs of dull knives.

Step 3Look at the face of the board you just jointed. Does the wood appear burnished at all? If it does, your jointer knives are extremely dull.

Step 4Finally, examine the shavings you just produced. Dull knives create limp and uneven shavings; sharp knives leave shavings that are crisp and even.