Helical vs. Spiral?

[Rob Will]

I have been in the market for a large jointer and planer (16"/24"):) .
Powermatic and Oliver appear to come out of the same factory and both offer a "helical" cutterhead.

There is some conflicting information in the sales literature ---especially Powermatic's. Both the Powermatic and Oliver appear to have replacable insert cutters (30mm wide?) that are mounted at a slight angle to the direction of rotation.

How do these heads compare to the Byrd "shelix" cutterhead?

[Paul B. Cresti]

I have been in the market for a large jointer and planer (16"/24"):) .
Powermatic and Oliver appear to come out of the same factory and both offer a "helical" cutterhead.

There is some conflicting information in the sales literature ---especially Powermatic's. Both the Powermatic and Oliver appear to have replacable insert cutters (30mm wide?) that are mounted at a slight angle to the direction of rotation.

How do these heads compare to the Byrd "shelix" cutterhead?
Rob,
I can add one word "Tersa". Why anyone would want a head with a milion little knives to turn is beyond me. All I need to do is tap down some gibs, slide out a knife, slide in or flip the exsiting over and repeat for all others knives. Then turn on machine and I am done.... takes about 1-3 minutes. I can also add one more thing if you are looking at both a J & P have you ever considered a European combo? I can think of a certain make that comes to mind ;)

[tod evans]

rob, in laymans terms a true spiral head will have the knife(s) striking the wood at a tangent, or skew. whereas a helical head will have the knifes striking the wood at 90deg to the grain as in a conventional cutter only the knifes are mounted in a helical (spiral) pattern. is there a reason you are looking at these heads? paul brought up a very valid point about the tersa heads. if you`re not dead set on a spiral/helical head the tersa is worthy of your consideration. .02 tod

[Rick Lizek]

If you do the reading at the site you should be able to determine the difference. The PM and Oliver heical heads use high speed steel flexible insert knives. The Shelix and other helical cutter heads use carbide inserts which can be rotated 4 times. The HSS insert knives are only good once. So when figuring cost comparisons remember the 4 times rotation and carbide lasts typically 8 time longer. HSS yields a sharper edge initially though. The tersa heads are a nice way to go. There is also the esta-knife system. Personally I don't think the steel in the esta knives are as good as the steel in conventional Wisconsin knife works blades. I have no problems with regular blade heads as I can change the knives on a 20" jointer within .0005" in 20 minutes leisurely but that's from lots of practice as a machine tech.

[Paul B. Cresti]

If you do the reading at the site you should be able to determine the difference. The PM and Oliver heical heads use high speed steel flexible insert knives. The Shelix and other helical cutter heads use carbide inserts which can be rotated 4 times. The HSS insert knives are only good once. So when figuring cost comparisons remember the 4 times rotation and carbide lasts typically 8 time longer. HSS yields a sharper edge initially though. The tersa heads are a nice way to go. There is also the esta-knife system. Personally I don't think the steel in the esta knives are as good as the steel in conventional Wisconsin knife works blades. I have no problems with regular blade heads as I can change the knives on a 20" jointer within .0005" in 20 minutes leisurely but that's from lots of practice as a machine tech.

Rick,
Not sure if you reference to HSS only good once was to Helix type heads but the Tersa knives have two sides to them. They are available in HSS, Chrome and carbide.

[Rick Lizek]

Rick,
Not sure if you reference to HSS only good once was to Helix type heads but the Tersa knives have two sides to them. They are available in HSS, Chrome and carbide.

I was referring to the HSS in the PM and Oliver type spiral heads. I am well aware of the dual edge and options on the tersa but you know how it is...tough to remember everything to post.

[Chris Rosenberger]

I have been in the market for a large jointer and planer (16"/24"):) .
Powermatic and Oliver appear to come out of the same factory and both offer a "helical" cutterhead.

There is some conflicting information in the sales literature ---especially Powermatic's. Both the Powermatic and Oliver appear to have replacable insert cutters (30mm wide?) that are mounted at a slight angle to the direction of rotation.

How do these heads compare to the Byrd "shelix" cutterhead?

Rob,
I have a 16" Powermatic jointer with the helical head. I am very happy with it. The cutters are 30mm wide & have 2 reversable cutting edges. The cutters stand up in the cutter head similar to a standard knife. They are at a slight angle & very easy to change. The Byrd cutters are 15mm X 15mm with 4 reversable cutting edges. They mount flat on the cutter head surface & at a slight angle. They are also very easy to change.

[J.R. Rutter]

I put the Shelix head in my 20" 4-post planer. I like how quiet it runs, and the fact that it is hard to make it tear-out tough grain. I run a lot of interlocked grain quartersawn jatoba, and love the performance.

I am curious about the Tersa head for my jointer because the shelix head leaves very shallow scallops the width of the cutters. For edge gluing, this might be an issue (?). Anyway, with the Tersa head, you can get a 4-knife head and run 2xcarbide and 2xsteel knives for combo of longevity and finish quality (according to the rep I talked to).

How does Tersa do on tough grain?

-JR

[Rob Will]

Thanks for the photos and thanks to everyone for the info.

[Barry O'Mahony]

I am curious about the Tersa head for my jointer because the shelix head leaves very shallow scallops the width of the cutters.That is a consequence, and an often unappreciated one, of skewing the cutters at an angle to the direction of rotation.

Basic geometry: if the cutters have straight edges, and you skew them, not all points on the cutting edge will cut to the same height. You simply cannot have a straight line (i.e., the cutting edge) all lie on the surface of a cylinder (which would be needed to get an even cut), unless the line is parallel to the axis of the cylinder. But that only happens if you don't skew the cutter.

For a skewed cutter, the edges need to be ground in the shape of a shallow ellipse in order for it to cut at the same height. The curve depends on the angle of skew and the diameter of the cutterhead. I've heard from one shelix owner that says his head uses cutters with curved edges (that have the diameter of the cutterhead marked on them), but I'm not sure they all do.