Advantages of Helical cutterhead for a non-professional planer [duplicate]

Question

From what I read, it would seem like this design is fundamentally superior to that of a three full-width blades. For context/example, I have a DeWalt DW735 planer. For the purpose of this question, we should put aside the poor quality of the blades that come with this planer (there are HSS or carbide replacement blades for it).

This is an example of a helical cutterhead for this planer. The machine blades are simply three full-width knives

Assuming that this design is indeed superior (as opposed to being simply marketing bullshit), could someone explain the physics/mechanics of why it works better?

Answer 1

As I understand it, one of the big advantages is that the blade actually slices diagonally across the wood instead of straight into it.

When hand planing, there is a very strong, natural tendency to put the plane at an angle across the direction of planing, not square to the edge of the board. This is accomplishing the same thing as the helical head. The blade can slide into the wood and cut a little bit at a time, making a smoother entry into the wood than if you try to push the entire cutting edge directly into the wood all at one shot.

This also gives an advantage of making it easier to push the cutting edge through the wood. When hand planing, it makes the work less tiring (important since it's human powered and humans get tired). I've see claims that this makes it easier on the electric motor driving your planer, too, since small portions of the blade are contacting the work piece at one time instead of the full width of the blade.

I've also seen claims that the full width of a straight knife hitting the wood slows the cutter head down "significantly" which the motor then needs to compensate for by reaccellerating the whole head, while the small knives have much less impact on the cutter head speed, allowing it to run more smoothly. I'm not sure how much credence to put into this last claim, but I've seen it made in more than a few YouTube videos by people who seem to (in general) know what they're talking about.

Answer 2

Well, I can say that they do work well. My dad bought A helical planer and most of the time you don't have to do any sanding when it's done.

The physics I believe actually has more to do with the many overlapping small blades, taking out smaller chips in each pass, at staggered intervals.

The smaller blades are less likely to have tearout and when it does it is generally going to be much smaller.

Granted a negative is you have a LOT of little blades to rotate when you need a new sharp edge. Though if you get a chip, you can just rotate the couple that chipped and continue on. You also have 4 sides to each blade to be used.

Answer 3

Helical blades are better by some measures than straight blades. Whether the difference is enough to justify a retrofit on a planer like the DW735 depends on what you're doing with the machine. The quality of helical blade retrofits is also very important. Close tolerances and fit are obviously important on any planer head that uses fixed (as compared to adjustable) blade positioning, but it's absolutely critical on helical heads.

The advantages:

• The individual blades are angled relative to the motion of the workpiece, and curved so that their intersection with the workplace all occurs in a single plane. Because of this, all cutting on a helical head is a shearing cut, rather than a "chop" cut, as with straight blades. This results in less tearout on difficult to plane woods (gnarly grain, burl, bidirectional grain runout). On a perfectly ground and provisioned head, it also makes for a smoother surface with less scalloping than with straight blades.
• Damage to a blade can be repaired locally, by replacing or rotating a single or at most 3 or 4 inserts, whereas on straight bladed heads that use pre-ground insert knives, one generally has to replace the entire knife set if metal, stone or even a particularly hard knot in very hard woods damages your knives. The cost difference can be very great, particularly if you're using straight carbide knives, which are very expensive.
• The knives are always carbide on a helical head, and thus last longer than typical straight knives found on non-industrial planers and jointers. This can actually pay for the head upgrade if you are planing a lot of gritty wood (like white oak), and going through a great many of the standard straight blade inserts.

There are some disadvantages, however, to helical upgrades on consumer style planers:

• They are expensive - typically at least a 50% increase in the cost of a tool like your DW735. The retrofits for consumer grade planers are also often not of the quality that oem helical heads on higher end machines are, which reduces some of the advantages of the helical heads.
• They seem to impose greater load on planer motors, at least on consumer grade machines. The continuous shear cut as compared to intermittent chops may be part of the reason for this, but it is also likely due to the fact that carbide is rarely as truly sharp as HSS knives, but on a helical head, cuts well enough when slightly dull that they are used in that condition for extended periods.
• Replacing or rotating knives on a helical head is a precision operation, and you must get the position and torque on the retaining screw right and uniform when you do, or you will get a noticeably ragged cut. Also, it is fairly easy to overtighten retaining screws, resulting in broken knives, or worse, broken screws (that potentially ruin the entire head).

I have a DW735 with Byrd helical head that I use as a finish planer. I like it. It's great for final planing of gnarly woods. However, it reduced the cutting capacity of my machine to 1/32" per pass (OK for a finish planer, but it'd be a pain if you're doing much milling to thickness of rough lumber) due to the Byrd head having a slightly smaller cutting radius than the standard DeWalt head. But if I were buying a planer to be the only one in my shop, I would probably take the money the upgrade head cost, and put it toward getting a wider, heavier, slightly more "industrial" straight knife planer.