Straight vs. “spiral” cutterheads

For many years, planers and jointers had straight knives. There was no option. You had your knives sharpened when they got dull or bought a grinding attachment for your machine and sharpened them yourself.

I remember when the first spiral cutterhead appeared, the Neuman helical head. It had four continuous knives that wrapped around the cutterhead. They were expensive! A 25 Delta planer with conventional straight cutters cost around four grand. With the Neuamn head, the price jumped to almost nine grand and that was not including the extra $1,500 for the grinding attachment. And you really had to get the grinding attachment because there were very few sharpening shops equipped to handle a spiral knife. Plus, the things were a PITA to adjust.

For many years now, we have had spiral insert cutters. These heads use “chips” instead of continuous knives. The chips can be rotated four times to provide a fresh cutting edge. There are a lot of advantages to these cutterheads. For one thing, if you nick a cutter, you only have to rotate a couple of chips instead of the whole set of knives. In a production setting, there is less down time because it’s faster to replace the chips than to install fresh knives which then have to be tediously adjusted.

The helical insert heads are not cheap. They are available for most planers but sometimes can cost as much, if not more, than the machine itself. The insert chips are not exactly cheap either. If you figure a hundred and twenty or so chips per head at three to five bucks each, even considering four edges per chip, that’s a lot of sharpenings of conventional straight knives before you “break even.” Also, these heads are prone to “ridging” because the cutter is not continuous like the Neuman heads were so the surface quality is not as good. Nevertheless, they still offer an advantage over straight knives when cutting difficult woods or highly figured stock.



  • Dwayne DeWhitt says:

    I used to sell for Leitz Tooling, and a top quality cutter head of this type, would not “ridge”, but may show a slight “color” difference. The knives are “insert carbide” and have a sharper edge than brazed carbide ever does, and lasts maybe 3 times longer than brazed carbide which is used for normal router bits and shaper cutters. As you said there are no sharpening costs, just rotate the carbide square. A top quality head will uniformly seat every knife easily, if the dust is blown out. The genius of the spiral is that only a small portion of knife is cutting at any time, thus reducing the work load on the machine.

  • Amous Maue says:

    I’m happy to see that someone agrees that the old straight knives were a pain to set. When the sharpening shop got to .50 per inch to sharpen my knives I decided to try chip heads. For five years I’ve had a 12″ jointer and a 20″ planer so equipped and though I don’t like the cost of the chips, considering the time they save, they’re a bargain.

  • Jeff Hurley says:

    Leith and Terminus both make insert tooling in a straight knife in either steel and carbide. My SCMI uses Leitz which are expensive but five minutes and your up and running. no pressure bar adjustment and the digital readout is always right. Ternimus makes insert tooling that can lift straight out of the head just needing to loosen two set screws. If you are not going to sand I’m still old school and prefer my straight cutters over my chip cutters

  • Dana Donovan says:

    Years ago the millwork company I work for purchased a 36″ Whitney planer with a Neuman spiral head. This is the best planer I have ever used. The noise level with a 30″ panel going thru was less than our 24″ straight knife planer idling. Sharpening was quick and easy with the grinder attachment and the knives lasted 4-5 times longer than steel knives. When the planer was installed, the company rep told us that the cut was so smooth that you could pass a board thru cross grain without any tearout. Of course, we had to see for ourselves so we ran a 2′ square maple panel thru sideways. It planed perfectly with only a slight increase in noise level! And I believe that Neuman still makes these spiral heads.

  • Ed Borys says:

    Okay so here it is 2012 and what is the story TODAY? It appears many of the companies that supply straight knives have made it much easier to adjust and or sharpen/change. So if cost is a major factor when choose’n – are knives now a better option? Over the years, some believe the spiral heads leave a “spiral track” on your wood. True or false?
    What is your view when it comes to pro’s and con’s of knives vs spiral?
    Thank you in advance if you share this knowledge.

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