Is a spiral head worth it?

This question comes up a lot on the forums I frequent. It generates a lot of comments and opinions are all over the place. So, I thought it would be good to put together the arguments for and against.

First, some terminology. Jointers and planers share the concept of a rotating drum (aka head) that has cutters embedded in it. These cutters cut, scrape or shear wood to make a flat, uniform surface. Straight blade heads have a small number of blades (2-4 typically) that span the entire width of the drum. They are perpendicular to the direction of wood movement. When the blade comes into contact with the wood, it scrapes a little bit off. Blades were almost always made of HSS so they didn't last that long and required resharpening. Until recently, this how all jointer and planer heads worked. But in the last 20 years or so, a new style of head has emerged. Instead of long straight blades, the cutting edge is segmented with short cutters (15 mm, about 5/8") and are positioned in a spiral arrangement so that only one cutter is contacting the wood at any one point in time. A more recent invention is a helical arrangement where the cutters not perpendicular to the wood movement but angled to provide a slicing action. This is called a spiral helix and the trade name by the manufacturer, Byrd, is shelix. I will refer to both types as spirals. All spirals have carbide cutters and are set up so that each cutter has 4 sides. When a side is damaged or gets dull, the cutter can be rotated to provide a new, sharp edge.

A spiral or helix head has a number of advantages. Because it takes smaller "bites" it is easier on the wood and has less tear out. It also makes less noise because at any point only a small bit of cutter is actually cutting. I have also heard that the spiral arrangement takes less energy and is thus easier on the machine. It makes sense but have not seen proof of that. Because the cutters are carbide, they last longer than straight HSS planer knives. Typically, 10 times longer. In addition, each cutter has 4 edges so a carbide spiral will last 40 times longer than straight HSS knives.

One of the less obvious advantages is how a spiral head deals with damage. It's not uncommon to discover that a board had a nail, screw or rock in it after running it through the machine. The result is a nicked cutter. A straight blade with a nick in it needs to be replaced. A spiral cutter is simply rotated to present an undamaged edge. At the worst case, the cutter can be replaced at a fairly low cost. Not only is it cheaper to get back up running but it's a lot faster too.

So far, the advantages of spiral technology seem to far outweigh traditional straight blade cutters. What are the disadvantages? Primarily it is cost. It can add 40-50% to the price tag. A 15" planer with spiral technology will cost around $700 more than a traditional straight blade one.

I have heard arguments against spiral technology that center around lifecycle costs - the cost of sharpening and replacing HSS straight blades vs the increased cost of the carbide spiral. It says that in the long run, it's cheaper to use HSS straight blades. In the time you would wear out the carbide cutters on a spiral head, you would have spent less on HSS straight blades and sharpenings. Basically, my back of the envelope calculations shows that to be true assuming no damaged blades. But this argument doesn't take into account lost time due to sharpening, replacement and alignment of the blades. Also, it fails to consider the issue of damage which is highly unpredictable. It only takes a couple of incidents to swing the cost balance back in favor of a carbide spiral head.

But, even if the life cycle cost of a spiral is higher, the benefits outweight the costs. More uptime, quieter operation, less tearout all add up to a much better shop experience.