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Flexible highspeed steel knives fit into angled groove providing a true

Smoother cuts and easier blade changes make a spiral cutterhead worth the effort.

T Chop or Slice? The

top board was jointed with conventional knives; the bottom board with a spiral cutter.

Starting with flat, square stock makes building a project a lot easier. That's why a jointer is a "must-have" piece of equipment.

But a jointer has some limitations. It can tear out rather than slice wood fibers, especially when working with figured woods.

The problem is, on a conventional jointer cutterhead, the knives are square to the board, creating

a chopping cut. While this design is easy to manufacture, it may not give the best results. And even with this simple design, changing knives can be a chore.

Spiral Design. To address these shortcomings, manufacturers have developed replacement cutter-heads using a spiral design, placing knives or cutters angled around the cylinder. The advantage of this

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approach is it produces a shearing, rather than a chopping cut. It's the same idea as skewing your block plane to make a smoother cut. The good news is, after-market spiral cutterheads are now available for most 6" and 8" jointers.

In addition to the spiral design, each of the manufacturers incorporates indexed knives for hassle-free replacement. But that's where the similarities end. When it comes to spiral design, each company has taken a different approach.

Basic Spiral Design. The first approach, by Sunhill, is a "true spiral" design. That is, each of the three high-speed steel knives fits in an angled groove in the cutterhead. The photos at the top of this page show the design.

To wrap around the spiral, the knives are thin and very flexible. Nevertheless, they hold up well in most woodworking applications. The downside is, if you get a nick in die blades you'll need to replace all three. Since the knives are indexed, you can't shift them to either side as you would with a conventional cutterhead.

Staggered Blades. The other two designs shown here take a different approach. Instead of long blades, they use a series of small insert cutters attached to the cutterhead with a countersunk screw.

ShopNotes No. 89