Re-Visit Cap Iron Video

[Jim Koepke]

This video seems to pop up in different places over time > https://giantcypress.net/post/231595...deo-created-by

This is the full version of the video created by Professor Yasunori Kawai and Honorary Professor Chutaro Kato at Yamagata University, as part of their research in the role of chipbreakers, which they call cap irons, in planing.

There are also a few links at the top of the page others might find of interest:

Japanese chisel setup Japanese plane setup Japanese saw sharpening Building a Roubo workbench

When watching the video, watch what takes place behind the cutting. This is why planes need to have a clearance angle behind the edge. It is most pronounced during the segment where no chip breaker is used planing against the grain.

jtk

[Jimmy Harris]

That's an interesting video. But I wonder, if those findings are correct, and I have no reason to believe they aren't, when why don't modern plane makers take advantage of that knowledge and make cap irons with steeper angles at the tip? Every cap iron I've seen seems to come to a sharp point instead of a blunt edge.

[Rafael Herrera]

I would guess the reason was "group think". If you read the articles and forum posts from before 2012 you see that the general consensus was that chipbreakers were there to strengthen the iron and "prevent chatter". That, despite the history of chipbreaker use since the 1750s with tapered irons and Japanese planes as well. Literature, like Nicholson's book, explaining the purpose of the chipbreaker. All ignored.
One possible reason modern plane makers keep making their planes with chipbreakers is that they are just copying the Bailey or Bedrock design, but w no deep understanding of how the plane works. They focus on telling us how flat the sole is, how square the sides are, how thick the iron is, how heavy the plane is. Kind of selling you the notions that "bigger is better", "precision is better", etc., but the effort invested where it doesn't matter as much.

I once asked Ron Hock about the chipbreaker function in mitigating tearout. I don't have an exact recollection of his answer, but my impression was that the chipbreaker wasn't viewed as a tearout mitigation device.

Rafael

P.s. I know there's a Bailey patent where chipbreakers, thin irons and chatter are mentioned. However the patent was for an extra bend in the shape of the chipbreaker, a really small modification. It's debatable that its actually of any effect. The chipbreaker was already part of the design of the plane, he wasn't patenting the chipbreaker.

[Warren Mickley]

At the time they were introduced, I pointed out that the "improved chipbreakers" were rendered ineffective. At the time plane manufacturers were selling high angle frogs and "bevel up" planes as remedies for tearout. They still promote these costly solutions to difficult grain.

The Kato information was introduced on another forum in December 2007. Todd Hughes and I advocated for double iron use at that time. Here is one response:

https://blog.lostartpress.com/2007/12/

When I quoted portions of Nicholson's 1812 work concerning the double iron, Larry Williams said you could not trust Nicholson because he was a tool monger. However, it was Williams who was a tool monger, not Nicholson.

[Rafael Herrera]

And to think the only thing he needed to do to make his plane work was to move the damned frog back a little to get rid of the clogging.

The experiment shown in the video is just the iron and chipbreaker, they did not add a "close mouth" to the configuration.

In retrospective, it's kind of obvious to conclude there's no good reason to close the mouth opening and that it is actually counter productive to do so.

It doesn't take feeler gauges to set your cb close to the edge. Here's one of my smothing irons with a normal setup and another where the cb is 3/32" back. That's madness.
20240401_114254.jpg

[Tom Trees]

I've only got a look at an untouched cap iron/chipbreaker recently,
and was under the impression that the leading edge of them were somewhat finished to a sharp point.

Thankfully there is evidence appearing nowadays, like in JimKingshott's old videos, which shows this not to be the case.
So indeed, the modern(ish) consensus of honing the leading edge to 45 degrees, (bar Warren's long preference for honing them steeper)
hasn't been all that helpful for some, should they still be disregarding the usefulness of honing the cap iron to a steeper angle than most gurus might have mentioned.
Screenshot-2024-4-1 Uncle Jim - Bench Planes - YouTube.jpgScreenshot-2024-4-1 Uncle Jim - Bench Planes - YouTube(1).jpg

Safe to speculate that many on the tube, will still stick to their guns, honing them @45 degrees,
as the disregard for the above steeper preference generates various facets of income for those in the game.

i.e selling very expensive hones, or selling the drip feed system of veiled sharpening tips/ other methods of working, when the going gets tough,
that is... for those not being aware of the cap iron's ability to retain a sharp edge of the cutter.
i.e by not getting tearout, thus not getting hung up slamming into knots or reversing grain, what will blunt a plane iron almost immediately.

[Cameron Wood]

And to think the only thing he needed to do to make his plane work was to move the damned frog back a little to get rid of the clogging.

The experiment shown in the video is just the iron and chipbreaker, they did not add a "close mouth" to the configuration.

In retrospective, it's kind of obvious to conclude there's no good reason to close the mouth opening and that it is actually counter productive to do so.

It doesn't take feeler gauges to set your cb close to the edge. Here's one of my smothing irons with a normal setup and another where the cb is 3/32" back. That's madness.
20240401_114254.jpg

I don't think so. The test is on dead-flat stock, in controlled conditions, testing one variable. Japanese planes set up for very fine shavings have a tight mouth opening. That's part of what produces the long flat shavings shown in planing competitions, but in real-world conditions the planes will have a relatively close mouth opening depending on their use.

[Rafael Herrera]

In those planing competitions they use a very particular type of wood, I think it's straight grained alaskan cedar. Whatever the wood they use it's a very particular kind and lends itself to the very thin shavings seen there.

I don't know how they setup those planes, but since the wood they use is a big part of the results they get, whether the mouth is tight or not is probably of little consequence.

I've tried to take very thin shavings off of regular wood species, with the grain, with the iron as sharp as I could get it. I think I got as thin as 10 or 15 micrometers in some cases. It was an interesting experiment, but totally useless for real work.

If the chipbreaker is close to the edge, there needs to be room for the shavings to pass. If you want to set the plane to take shavings thicker than .001", there needs to be room for the shavings to pass.

It does not take much to confirm this. Set the frog back so you can see through the mouth when the double iron is installed. Take some shavings at different thicknesses. Examine the quality of the surface produced.

Next, close the mouth and watch your plane clog.

[Eric Brown]

Maybe there are two things to consider. First is that the blade cuts into the wood and the angle lifts it up. Second, is that when the shaving continues to travel up the blade, the shaving is starting to create pressure lifting the shaving off the cutting edge. Now the trick is to fold the shaving back on itself to counter that pressure. A chip-breaker controls the folding back. A sharp edge on the chip-breaker creates a different angle - higher- which does counter the pressure somewhat. A blunt chip-breaker create an even stronger counter pressure. So which is correct? Depends on both your wood and the thickness of your shaving. Is one better for soft and the other better for hard woods? I don't know. I do know that the chip-breaker has to be tight to the blade and close to edge. Now if you think about the edge of the chip-breaker being at a higher angle, it helps explain why higher angled blades can handle difficult woods. Heavier planes can keep the blade engaged better. The downside is that steeper angles, heavier shavings and heavier planes all make you work harder.

[Keegan Shields]

"Improved chip breaker" might be marketing double-speak for "cheaper to manufacture"

Obviously, I don't have data to back that assertion up, but many compromises are made between designing (or redesigning) a product and producing it at scale.

Just something to consider.

[Tom Trees]

Honing mine a conservative 50 /51 degrees, I haven't really found a down side for the two planes I use,
(not my rougher set jack-scrubby plane)
The cap iron actually working, on my Bailey planes, means less effort for me, as the plane doesn't get halted.
That's my 5 1/2 with no greater distance than 1/32" from the edge, heaviest shaving practical, in densest example of interlocked timber I use below...
SAM_3411.JPG

And smoother with no greater distance from the edge than 1/64"
SAM_5130.jpg

The "no greater distance" is importantly related to the camber of the iron, i.e, I can't set the cap that close if the iron is more cambered,
as the corners of the cap would overshoot each side.
(That's with the cap honed at 50/51 degrees. and I haven't played around with going steeper in order to attain more camber.)
and no tight mouths for me.

BTW, Thanks Warren.
Tom

[Cameron Wood]

In those planing competitions they use a very particular type of wood, I think it's straight grained alaskan cedar. Whatever the wood they use it's a very particular kind and lends itself to the very thin shavings seen there.

I don't know how they setup those planes, but since the wood they use is a big part of the results they get, whether the mouth is tight or not is probably of little consequence.

I've tried to take very thin shavings off of regular wood species, with the grain, with the iron as sharp as I could get it. I think I got as thin as 10 or 15 micrometers in some cases. It was an interesting experiment, but totally useless for real work.

If the chipbreaker is close to the edge, there needs to be room for the shavings to pass. If you want to set the plane to take shavings thicker than .001", there needs to be room for the shavings to pass.

It does not take much to confirm this. Set the frog back so you can see through the mouth when the double iron is installed. Take some shavings at different thicknesses. Examine the quality of the surface produced.

Next, close the mouth and watch your plane clog.

Here's a video that goes into some detail. About 6 minute to 8 minute is discussion of mouth opening.

https://www.youtube.com/watch?v=8IdRIDcAxKQ

Clogging the mouth is definitely an issue. For Japanese planes, often different ones are set up for level of cut. Here are some of mine- finer cut on the right, and heavier on the left. .5mm is about the smallest mouth that I go for.

IMG_4892.jpg

[Rafael Herrera]

That's not my experience with metal Bailey style planes. If you close the mouth and move the cb down, the plane will clog under normal use. The reason is that with the cb so close the shavings are deflected into the front of the mouth and clog.

I've a couple of Japanese planes with chipbrakers, the geometry of the cb is not the same and it may allow for the mouth to be tighter. The geometry of the throat, the front of the mouth or "wear", may also be such that it allows for the shavings to pass.

That a tight mouth is a method to mitigate tear out is a well known technique. It's used in bevel up planes, those fancy metal mitre planes, etc. It works, but as your collection of planes show, you need multiple planes to achieve your desired result.

A Bailey plane with a well fitted and prepared cb, unencumbered by a tight mouth, will work under a wide range of planing situations, not just smoothing.

Of course, one could file the back of the mouth of the Bailey plane at an angle leaning towards the front of the plane to make room for the shavings. This can be accomplished without widening the mouth. It's an option if one really insists on having a tight mouth.

20240401_155329.jpg

[Rafael Herrera]

Maybe there are two things to consider. First is that the blade cuts into the wood and the angle lifts it up. Second, is that when the shaving continues to travel up the blade, the shaving is starting to create pressure lifting the shaving off the cutting edge. Now the trick is to fold the shaving back on itself to counter that pressure. A chip-breaker controls the folding back.

A sharp edge on the chip-breaker creates a different angle - higher- which does counter the pressure somewhat. A blunt chip-breaker create an even stronger counter pressure. So which is correct? Depends on both your wood and the thickness of your shaving. Is one better for soft and the other better for hard woods? I don't know.

I do know that the chip-breaker has to be tight to the blade and close to edge. Now if you think about the edge of the chip-breaker being at a higher angle, it helps explain why higher angled blades can handle difficult woods. Heavier planes can keep the blade engaged better. The downside is that steeper angles, heavier shavings and heavier planes all make you work harder.

That's the function of the chipbreaker, to bend the shavings upwards so that the iron cuts the fibers before they lift the fibers ahead of the cut and cause tear out.
Without it, the shaving pull the fibers off in an uncontrolled way.

A steeper bed angle counteracts the lifting. This has been known all along, the problem is that a higher bed angle makes the plane harder to push.

The geometry needed is somewhere above 50 degrees and up to 80 to 90 degrees, this angle is measured at the point where the cb meets the face of the iron. The height of this bevel is not high, the chipbreaker starts rounding and that angle drops. The snapshots from the video gives you an idea of the angle. The chipbreaker for a hand plane has the necessary angle, but it also differs from the experimental setup.

Screenshot_20240401_230600.jpgScreenshot_20240401_230717.jpg20240331_100341.jpg

Here's a video, probably older than the professors Kawai and Kato video, where several planing scenarios are demonstrated using a wooden plane with and without a chipbreaker:


Rafael

P.S. Here it should be noted that the japanese study was designed to study the effect of the chipbreaker on a powered device called a "super smoother". I've been told the professors made another study focused on hand planes, but I don't have a link to it.

P.P.S If one wants to experiment the effect of a havier plane, one needs not to go out and buy a boutique plane, but simply to lean on a regular plane. Leaning on a plane adds many more pounds of pressure than the extra one or two pounds that a boutique plane adds to the mixture.

[Cameron Wood]

The title of the film is "the influence of cap iron on hand plane", so not surfacing machine.

I don't think there is a secondary bevel on the chipbreaker of those.

https://www.youtube.com/watch?v=R-E9LqxJ5IY