Chip Breakers

An old video has resurfaced and now it has been subtitledThe magnificent Wilbur Pan, rides again!

This video has an odd enough history of impact.  I have even heard it argued, in absence of the actual video, that it proved that chip breakers did not work.

There has been such a current of downplay on chip breakers, that when I originally wrote this article, I decided that I was not yet ready to publish it.  There are some very talented and skilled woodworkers, some of them with a great deal of historical background, that would strongly disagree with me.  A lot of these craftsmen are of such skill that I doubt I will or even could come close to the mastery of woodworking tools that they command.

But with this video link available, I feel a bit more confident.

When power tools came, the way things were made changed.   New materials, dimensional lumber and methods that did not have as steep a learning curve transformed the woodworking industry.

Things could have been, but were not made terribly better.  They were made faster, and less training was needed.   As power tools took over, many skills were forgotten.   Apprenticeship died and so did a lot of traditions.   A lot of skills survived, but the reasons for doing things they way they they are often got lost in the tumble.  There are mysteries still.

One odd ‘mystery’ is the appearance of the chip breaker.   In a field where change was typically slow, this innovation swept in quickly.   While many of us respect the wisdom and skill of these craftsmen,  the sudden adoption of the chip breaker perplexes quite a few students of classic hand tools.    On the web it is not been rare to hear and capable, respectable craftsmen debate with certainty as to the value of a chip breaker.

I started out with no opinion.  Then I fell in love with high angle and low angle planes.   Since high angle planes don’t have much use for chip breakers, and bevel up planes have no use for chip breakers, I became strongly in the camp that felt that chip breakers are an added complexity and hardly worth the time. They increase your adjustment complexity and tune up complexity while helping cause jamming.  I had also read advice from some fairly brilliant sharpeners who advised you to put a bevel on the back of the blade.   Chip breakers do not typically work well with back bevels.

So I fell into the ‘Chip Breakers are Useless Camp.’  Keep in mind that I had made several very nice planes and my best ones did not have chip breakers.  I did not argue the point much, since many of the folk arguing on either side, were way more advanced woodworkers than I will probably ever be.  But if you had asked me, during the three month that I was a member of this camp,  I would have told you that chip breakers were at best good top irons.  The combination of a softer iron top and a harder iron for cutting reduced vibration.  The top iron also allowed a thinner iron to be sold and used.  I figured that it was scarcity of steel that made a top iron desirable.  Odd thought that, when you consider that folk were beginning to move to iron planes, and the top iron combined with the bottom iron was definitely more machining and just as much iron.

While doing way too much planing, I came to the conclusion that back bevels were not the easy way to maintain blade sharpness or life over time.   Back bevels are a great way to appear to be a brilliant sharpener while doing a demonstration, but for day to day work, it makes sharpening the actual edge more complex and eats blades.  Stropping early and often turns out to be a much better method.   By giving up on the back bevel, I eliminated the most critical bit of resistance to using a chip breaker.

Then when reading a heated argument about chip breakers where one brave and brilliant woodworker was defending them against all comers, I realized that I had strong bias, but those biases were developed before I became good at tuning and adjusting planes.  My anti-chip breaker position fit in well with those biases, but I could not actually support my beliefs.

I had recently obtained a few relatively inexpensive Japanese planes with chip breakers. These planes will work just fine without the chip breaker. The thick tapered blades wedge to the wood and need no stabilization from a top iron.

So while I was experimenting with these  Japanese Planes, I decided to do a nice solid test so that I was not just repeating the chip data that research, photos, and brilliant arguments that all agreed that chip breakers were barely useful and a big pain. So I tuned up a blade and chip breaker to absolute precision.   I adjusted chip breakers the way that people who use them say you should.   I really did not expect to find any amazing improvements.  I had sharp blades and tight mouths, how was a chip breaker going to improve on that?   Well I was wrong.  By actually testing chip breakers, I found that they made a very big difference in the surface left behind.

My bias, learned back when I had no feel for grain, and thought oak was really hard wood, had made me vulnerable to the group consensus.  Here is what I found out.

If you are able to make a flat surface, then you can match a chip breaker and blade so that splinters never wedge between them. This solves the first issue I had with them. If the surfaces are smooth and you match them up and clean them up properly, jams are not caused by them either. So if you can tune a plane, a chip breaker does not cause a lot of problems.   With a well tuned plane, there is no real reason to fear or hate a chip breaker.

A top iron is not hard to line up exactly with a bottom iron. On a Western Plane, you loosen the screw that holds them together, rest them edge down on some wood, and tighten the screw. To get the bottom iron a touch forward of the bottom iron, you just lean then a bit and then tighten the screw. Seriously how hard is that? On a Japanese Plane you have to tap it into place, but once you develop the knack, it is much more convenient than doing adjustments on a Western Plane. I can do all this with ease, and I am not in the same league with a lot of the folk out there using planes. So fine adjustment, once you are reasonably skilled, is not a problem either.

So the problems that chip breakers create are close to negligible for a skilled craftsman. While they are not horrible, what good are they?

They reduce back wear on the blade. Wear on the back of the blade, is what eats blades fastest. By lifting the shaving off the bottom iron, wear is reduced. Oddly enough, by having the right clearance angle over the blade, in some cases the edge will start the cut and then only occasionally actually touch wood. So in some cases, the edge life of a blade can make a leap off the chart while still making a glass smooth cut. So first and foremost, a chip breaker can reduce your time sharpening and increase your blade life.  With just that, suddenly a chip breaker is a pretty nice thing.  When compared to a low angle, bevel up blade, the wear is night and day.  A bevel up plane needs much more metal removed to clean up and restore a worn blade.  So the equivalent simpler and as effective blade, costs more over time.  A lot of that cost is sharpening time and materials.

The ‘chip breaker’ advantage of a chip breaker requires fine adjustment. As the blade edge on the top iron is moved closer to the blade edge on the bottom iron, the plane begins to act more and more like a high angle plane. If they are quite close to even the plane becomes a high angle plane. This means that with very fine adjustment, you can in fact choose the behavior of your plane. A lot of folk talk about keeping the top irons edge within a thirty-second of an inch from the edge of the bottom iron or it does nothing. That is not entirely true, but for the sake of argument, that’s close to three hundredths of an inch. If you can’t make settings that are a lot finer than that, then you can’t adjust a smoother.  A thirty-second of an inch is a very fat chip.

Anyone with a chip in this argument can tune up and adjust a plane to cut a shaving that is a thousandth of an inch thick.   Adjusting a chip breaker this close should not really be a terrible challenge.   A thirty-second of an inch might be fine tuning for a table saw, but on a smoother a thirty-second of an inch is not even close.

If you have a sharp even chip breaker, you can tap the chip breaker almost right up to the edge of the blade, and take a folded type chip out. This allows you to plane harder rougher wood with the same plane that does well on soft. with the chip breaker just a half a hairs width back from the edge, the blade will handle odd wood grain quite well.

With the chip breaker back to the normal hairs width from the edge it can take a nice, full blade width, shaving out with ease.  You can also pull back the chip breaker if you are trying to hog out lots of softwood quickly.

This gives you at least four planes in one.  Four quality planes in one.  No wonder the old time experts converted to chip breakers .  Yes there are a lot of odd opinions on top irons used as chip breakers, and I find that I am in disagreement with some craftsmen that are far beyond me in skill. I love chip breakers and I know from observation and experience that they work great.

For an occasional craftsman who dreads taking a blade out or adjusting a plane, a top iron is horrid. For a craftsman who has a hundred planes on the wall, a top iron may be just another thing to fiddle with while trying to do work. For a craftsman with less than a dozen planes, or a craftsman who carries his tools, I believe that it is well worth his time to learn how to use a double iron.


9 comments to Chip Breakers

  • Stefan

    Hi Bob,

    Double irons are indeed very useful for standard angles and lower. I recently did some tests with various wooden planes (including Japanese) and quickly came to the same conlusions as yours. I also believe that the cap iron has a heatsink function to keep the edge cool and thus at least a bit more wear-resistant.
    There happens to be some confusion around about this topic so I’m glad to read this on your blog.

    Regards Stefan

  • Skip J.

    Hello Bob;

    When I first started tuning metal planes I read a number of expert books and web articles. Only a few, but the very best of them advised working over and tuning the cap iron to the same degree of finesse as the blades. So I started from the beginning with well-tuned chip breakers and was broke-in quickly as to positioning and it’s effects. I have never been able to get results on swirly grain as good without a chip breaker as with one, all other aspects of the plane being equal.

    Thanks to Wilbur for the proof, and to you for supplying it to us…


  • Bob Strawn

    Right now it is a kind of magical feeling on the forums. People who have experience with and understanding of chip breakers can have conversations about chip breakers. In the past they had to defend reality and were a bit scared to offer their full data, having seen how torn to shreds those who were forthcoming often became. There is still a lot of mystery and unanswered questions about chip breakers. Now perhaps data can be shared a bit more freely, and experiments can be made.


  • Kees

    Thanks for this article Bob. Some interesting things to think about and experiment with.
    The last few weeks have been fun with all the talk about the chipbreakers.

    Wilbur published the video with the translation. Bill Tindall on Woodcentral started this recent discussion. He dug out the vidoe and articles from Japan and arranged the translation by Mia Iwasaki. The real hero of this story is of course prof Kato who did the research back in 1989.

  • W Mickley

    Kees, this recent discussion was started by Bob Strawn on Sawmill Creek on 3/2/2012. David Weaver, who was part of that discussion then learned to use the double iron and discussed it with me on Woodcentral on 3/26. Bill Tindall joined the discussion with us on 4/9. Kees joined the discussion on 4/22 and reported success by 5/4. Without four of us, Kees, David, Bob and I, admitting to success like this, the video would have been rather hollow.

  • Bob Strawn

    I would add bravely! There were a lot of very wise, even brilliant woodworkers who stood squarely against this.

    On my part I was not so brave. I presented my truth, but I stayed mostly to the sidelines as more accomplished woodworkers thundered.


  • Kees

    Aha, I see Warren. My timeline was incomplete.
    Bill did do a lot of legwork to get in contact with Japan and bring us the video back again.

    Bob, how are your planes coming along?
    I have just finished the restoration of a nice line of wooden planes. All my own plane making plans went out of the window when I saw the Kato video. There are still so many double iron wooden planes around, it doesn’t make too much sense to make your own. But, who sais “sense” is a virtue?

  • Bob Strawn

    I am trying my hand at kanna making now, Kees. Foolishly I want to make them with pecan. Oak is beginning to seem like a soft wood to me.


  • Joe

    Here is a vimeo video of Cap irons on a plane an eye opener for sure…


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