Helical vs Spiral vs Straight Knife Planers

[Gavin Egersett]

Hello!

I'm looking at getting a benchtop planer due to space constraints. I know there are three types of cutterheads that can be chosen but I've heard a multitude of different answers on what is "best." So my questions are as follows:

1. Of the three, which would provide the cleanest and smoothest cut?

2. Does a single speed helical at 25 fpm beat out a two speed spiral or straight knife option at 16 and 26 fpm options?

3. Recommendations on options that have worked well for y'all? I plan to do work with hardwoods if that matters.

Thanks!

[stephen thomas]

Does "spiral" relating to a cutterhead mean individual insert teeth?
(I think i have a few true spiral cutterheads, for taper mills, but don't see how that would be applicable to a planer, so the term must mean something different?)
IOW, how does a spiral differ from a helical?

Or is helical like the heads on my Diehl lumber jointer, where the knives are straight, but the cutting edge is helical?

Always interesting to sharpen.
I'm selling the machine, so just set up and sharpened the near-side head recently.
These are old photos from when i was rebuilding the machine, and my early digital camera intermittently decided it didn't want to do color anymore:

Img3926Watkins Glen.jpgsmt_diehl66017 - Copy.jpg

[lou Brava]

Well if there's a budget than that will play into what you get & how often are you going to use it. I had a budget and bought a Cutech sprial 2 speed planer. It has worked very well on all various types of hardwood. I don't think any bench top would produce a "better" cut but I'm sure a Delta 735 would last much longer under daily use. But since I'm hobby WW I'm pretty confident the Cutech will out last me. The Cutech was designed with a sprial head that's another reason I chose it over the Delta. If I was to do it again I'd save my penny's for a 15" planer I found that long thick 2"-3" stock seems to put some stress on the smaller bench top motors due to the weight of the materiel.

[George Yetka]

The main advantages I see in the spiral heads is that the inserts last longer even if they were single sided and not 4 sided. The process is far quieter with helical (no ear plugs needed in most cases). For a benchtop planer you can expect to pay $600 more than straight knife but the cost of a set of blades on say a 735 is $55 and you get 1 flip and they are unsharpenable. The helical inserts the byrd helical head set is 525 for this unit and a fresh set of inserts is $180. In the 3 years I had a 735 I went through 4 sets of additional blades. My guess is I would still be on the original set of inserts on the Byrd and most likely just moving to the 3rd side. With that math the Byrd would be paid for in the first 5 years or so in saved cost of blades. and at the 7 year point your saving

The advantage of using the spiral make it worth it.

2 speed will allow you to slow the feed for a cleaner cut in wood prone to tearout.

2 speed helical would be my pick in the bunch

[Holmes Anderson]

I assume you have a freestanding jointer. If floor space is a problem, then maybe consider J/P combo machines.

[Brian Gumpper]

To me nothing will cut better than a sharp steel knife being there are no transitions between the cutters like on an indexable insert head. But the heads like the Byrd have other advantages I appreciate more such as longevity of the carbide cutters, reduced tearout, reduced noise and better chip collection. Whatever machine you consider also consider the replacement blades/cutters because there are some proprietary ones out there that are more expensive than they should be.

[David Walser]

Gavin -- Allow me to address your questions in the order you asked them:

1. Everything else being equal, helical heads produce the cleanest and smoothest cuts. Spiral heads and straight knife heads provide cuts of equal quality. The reason helical heads tend to produce better cut quality is because the cutters engage the wood at a shear angle. (This assumes the wood runs straight through the planer.) Both spiral and straight knife heads engage the wood head-on. (Of course, if you're running narrow boards through the planer, you can run them at an angle to produce a cleaner shearing cut.)

2. The question you asked about feed rates cannot be answered based on the information you gave. More important than feed rate is the cut-per-inch rate. This is based on the RPM of the cutter head, the number of knives (or rows of cutters), and the feed rate. Most benchtop planers have a 2-knife head (or the equivalent spiral or helical head). So, to me, the number of knives is the most important thing to look at in terms of cut quality. The DeWalt 735, with its 3-knife head, does a better job in terms of cut quality than most helical planers with the equivalent of a 2-knife head. This is true whether you're running the DeWalt 'fast' or 'slow' in terms of feed rates. That extra knife makes a big difference.

3. If you can afford it, go with the DeWalt 735x. It's a beast of a planer and produces a very nice cut. With highly figured woods, the slower feed rate will help reduce tear out (as will running the boards at an angle through the planer). If you cannot afford the DeWalt, take a look at the new Hercules 3-knife planer from Harbor Freight. I've not used it, but I've heard good things about it. It has the same number of knives, the same feed rates, and the same cuts-per-inch as the DeWalt 735. The DeWalt is a better machine, but it costs twice as much and the wood won't know the difference.

With either planer you might, eventually, want to upgrade to an helical head. Not for cut quality, but for creature comfort. Spiral and helical heads are quieter than straight knife heads. The reason is a straight knife planer takes a series of full-width bites out of the wood as it's fed through the planer. Spiral and helical heads take several partial-width nibbles. Big bites are louder than small nibbles. As discussed above, helical heads in theory produce a higher quality cut due to their shear angle of attack. In practice, you'll be hard pressed to tell the difference in cut quality (assuming the cutters in both heads are equally sharp). Which brings me to the biggest advantage of helical and spiral heads -- keeping their cutters sharp is far easier than with a straight knife head. With helical and spiral heads, you simply rotate the one cutter with a nick. With straight knives, you move each blade slightly to the left or the right so the nicks in each blade do not line up. Also, helical and spiral heads often use carbide cutters (some use HSS cutters), which will last much longer than straight knives made from HSS.

HTH

[Warren Lake]

feed rate is huge, being able to control it over and above many planers is the difference between blow out and clean cut. When I have time ill be putting a gear motor on the SCM and maybe the wadkin as well or just half the feed rate range on that one.

[Jimmy Harris]

Taking smaller cuts is the best way to get a clean cut. You can do this by slowing the feed rate on some models, and by taking shallower cuts. Of course, if you have to lower the cutter head speed to get the lower feed rate, then all you do is lose speed. The reason why a lower feed rate is supposed to cut cleaner is because you're slowing the wood through the cutter, giving the cutter more time to perform more cuts per square inch. Thus taking smaller bites.

A spiral head and a helical head are pretty similar. The Helical just has more than one spiral going around the drum. So a helical head is better, because you get two cuts per section, vs. just one, due to the second spiral. The biggest advantage over straight blades is they tend to last longer. They usually have four cutters per blade, as opposed to two, so you can rotate them more. Plus, they tend to be made of harder steel. They also tend to do better on some highly figured grains, as they cut at an angle. However, if you take a shallow enough cut with a straight blade in highly figured grain, you should still be able to avoid tear out. Straight blades also tend to give a smoother finish, but only with fresh blades and when everything is properly set up. Helical and spiral heads tend to give a smoother finish in less-than-ideal conditions.

My point being, none do something the others cannot do. But the helical heads tend to be more forgiving. I too would prioritize feed rate over cutter head style, as that seems to make more of a difference in my experience. That and reading the grain and knowing how to set up the machine.

[Andrew Hughes]

I disagree with David about how insert head like Bryd cut.
Inserts engage the wood with a 30 degree facebevel if they didn’t tilt the inserts the 6 or 7 degrees the power consumption would be unacceptable. Almost forgot the slight radius that’s needed for a insert head too.

Anyone can add 6 or 7 degrees face bevel to straight knives and produce the same kind of scrapping cut. The bevel acts like a chip breaker just like a double iron plane iron.
The price for the 6 or 7 face bevel is more power consumption and the heat that will from the scrap is hard or Hss.
This has to be the reason inserts are Carbide. They would not last very long.
For many of us it’s not easy to understand the science behind cutting wood. I felt the need for myself to study this topic for I am a woodworker and it’s part of the process.
If your interested look up hook angle and compare that to forward rake. Look up clearance and sharpness angles.
The internet can be a great teacher. Unfortunately content creators on YouTube are spread a lot of nonsense
Good Luck

[stephen thomas]

Aha!
steve (me) posted:

Does "spiral" relating to a cutterhead mean individual insert teeth?
(I think i have a few true spiral cutterheads, for taper mills, but don't see how that would be applicable to a planer, so the term must mean something different?)
IOW, how does a spiral differ from a helical?

I was not familiar with (modern?) cutterheads since about the time of the Oliver ITCH heads, which are helical.
Based on info in a number of follow-up posts, i did some googling and see that ad-speak has co-opted geometry.
A "spiral cutterhead" is indeed the straight insert teeth, arranged on helices around the perimeter of a cylindrical cutting circle. (I think?)
And "helical" means the individual cutters, also placed along a helix, are also sharpened, (Like ITCH heads, and like the old skew-knife arrangements such as the Diehl heads) to a true segment of a helix.

Sorry, no opinion of which would be better.
I really like the Diehl, and one or two rare, ancient jointers that have up to at least 12" wide skew knife heads, sharpened to a helix.
But i also like not paying for inserts on my 4 knife planer.

If i still had employees, inserts of either style would certainly be of interest. Fast, accurate re-sharp when something "bad" happens to a knife. Even swapping a full set of inserts would be efficient, because someone else (customers) are paying you to stay productive. Oliver ITCH heads are really cool, but you have to have the factory sharpening rig, and sharpen in the machine. If the inserts are carbide, the dust is a pernicious biohazard not worth dealing with.



smt

[Bill Dufour]

FPM must include number of knives, two, three or four are common. A four knife cutterhead at any FPM feed will do a nicer cut then a two knife head at the same FPM. Insert or the powermatic quiet head are harder to say how many knives they have.
Bill D

[Michael Schuch]

My straight blade planer was starting to have excessive tear out and leaving grooves after ~10 years. A new set of knives and it cuts as good as new now. I was intimidated with the knife changing procedure so I put it off much longer than I should have. It was much easier to change the knives than I had expected. For a bench top planer I would look at ones that has the quick change double sided blades that mount on registration tits.

I have always had the impression that the helical insert heads are better than straight knives for finish especially on figured wood... but my straight knives have always done an excellent job for me.

[George Yetka]

My straight blade planer was starting to have excessive tear out and leaving grooves after ~10 years. A new set of knives and it cuts as good as new now. I was intimidated with the knife changing procedure so I put it off much longer than I should have. It was much easier to change the knives than I had expected. For a bench top planer I would look at ones that has the quick change double sided blades that mount on registration tits.

I have always had the impression that the helical insert heads are better than straight knives for finish especially on figured wood... but my straight knives have always done an excellent job for me.

Michael was this a floor model with sharpenable blades? 10 years is a very good run for a blade set. Benchtops have very thin blades most of which are not capable of being sharpened

[Richard Coers]

feed rate is huge, being able to control it over and above many planers is the difference between blow out and clean cut. When I have time ill be putting a gear motor on the SCM and maybe the wadkin as well or just half the feed rate range on that one.

Sending the board through the planer in the proper direction is far more important that feed speed. Feed speed is just about cuts per inch for a smoother look, but it does little to change tear out, Does your hand plane, going the wrong way, produce a better cut when going slow?