Why does my new spiral cutterhead for my jointer leave grooves?

The many square cutters on a spiral cutterhead make adjustments easy but typically leave a slightly less-finished board.

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Blue chalk reveals the slight linear peaks—separated by shallow valleys—caused by the convex blades of a spiral cutterhead.

Q:

I recently bought  an aftermarket spiral cutterhead for my jointer. Now when I use it, the face of each board shows slight grooves running along its length. Am I doing something wrong?
—Travis Adair, Cincinnati, Ohio

A:

Probably not, Travis. We’ve found similar results in our tests of spiral cutterheads. The small individual blades that corkscrew around the cutterhead have slightly convex cutting edges that fight tear-out, but also leave the linear striations you’re noticing. So if you’re used to a nearly finished face out of your straight-knife cutterhead, you might be disappointed by the additional sanding burden added by the spiral cutterhead.

Still, a spiral cutterhead brings several advantages: Where tear-out-prone straight knives can wreak havoc on highly figured woods, spiral heads shear the wood without damage. Also, straight knives can be a hassle to replace and adjust. Not so with spiral cutters. When one edge of the small four-sided, self-indexing cutters becomes dull or nicked, simply rotate them 90° to bring a fresh edge to bear. That adds up to four times the cutting life. And that’s not counting the fact that many of the replacement spiral cutterheads use long-lasting carbide rather than high-speed steel. At pennies per replacement cutter, you won’t break the bank when you need to replace one, either.

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