Cap iron for a cambered blade

[Mike Holbrook]

Paul,

Thanks for that video. I have watched other videos from the same English gent and almost did not watch the whole video. Glad I continued on with it because he says several things that match my experiences/habits closely.

First of all I am less interested in perfectly flat surfaces and planes that take whisper shavings. I understand the interest in this type of work but it just does not apply to most of the work I want to do, which as the video points out more often involves thicker shavings. Whisper thin shavings seem to me to apply much more to how sharp one can get a blade and how precisely one can set a the chip breaker.

I was interested to see that he works his cambers and sets his chip breakers the way I do. He uses the full width of his blades, fading the camber out at both edges. I also habitually set my chip breakers at the far edges of the cambered blades to maximize shaving width. I suspect this is the point Steve Voigt and others are making above too.

I still may experiment with a LV chip breaker, just to see...

[Paul Sidener]

Glad it helped Mike. There may be a time you will want the whisper shavings, but on a day to day work it isn't always necessary. Richard has a way of explaining that is easy to understand, once you get past the English accent.

[Steve Voigt]

"Simply put, the deeper the cut, the farther back the cap iron needs to be."

Maybe - well not really maybe, no. Anybody with a very close cap iron setting on their smoother can walk out to their shop and taking a hogging cut, as compared to a typical smoother pass. Try it. It's a bit of a hard(er) push but that's about it.

Well, I certainly have tried what you describe. I generally don't write about things I haven't tried, and I have tried most things when it comes to cap irons. There is simple physics here: you can't take a cut that is as deep as the distance from cutter to cap iron. If the cap iron is set .005 from the edge, you can't pull an .005 shaving. If you try to, the cap iron will be below the sole and the plane will not cut. I believe you when you say you are taking "a hogging cut," but I bet the cap iron is not set nearly as close as you think it is.

There are absolutely times when surfacing roughsawn but figured stock a fully cambered cap iron on a jack plane would be a lovely thing to have. There's no law that says you can't move it back an 8th or up to a 32nd (or closer/farther). If the cap iron shape is right it's dealer's choice. The cambered cap iron also serves as a handy templet (template) if you like to produce the same shape at the end cutter over and over again. Once the cap iron is shaped to fit requirements, you're golden. Cambering the cap iron on your jack plane adds a whole lot of value and versatility -- you can hog, for sure, and you can also bring it in close if the operation is producing too much tear out but it's too soon to use the smoother, i.e, the board isn't out of wind, free of other warp, etc. and you'd like to keep a longer plane on the workpiece until all of this is eased out.

I don't really know what to make of all this. You keep asserting that there are all these benefits to a cambered cap iron, without any evidence or details. But as far as "hogging" vs. "bringing the cap iron in close" goes, you can do that just as well--better actually--with a straight cap iron. Let's say you have 1/16" of camber and you want to set the cap iron 1/32" from the edge (at the center, where the cut is deepest). No problem, you just hang the corners of the cap iron past the cutter. This will work fine, as long as your depth of cut doesn't exceed 1/32". No, it will not damage the cutter. If you cambered the cap iron, it wouldn't change things one iota; your max. depth of cut would be exactly the same.

The best thing that can be said about cambering the cap iron is that it's a waste of time that doesn't improve performance. The worst thing that can be said about it is that you can permanently screw up a nice cap iron. I argued about this with Dave Weaver a couple years ago. Then I went and carefully cambered a cap iron on a jack, and spent a lot of time playing with it. He was right; I was wrong. You are late to the party.

"
Maguire's advice misses the mark a bit, though he is by no means the first person to assert that strategy. Unfortunately it's flawed advice, and takes away a lot of finesse you ought to have with your jack. It takes nothing away from a jack's ability to hog off material, either. Classic win-win.

Yeah, see Richard is a guy who has made a living with hand tools for most of his life. He told me a little about how he was taught to to use the cap iron, at an age when you and I were studying freshman algebra, decades before hobbyists were watching the Kato/Kawai video. One thing I have noticed about guys like Richard, they prefer simple, no-nonsense solutions and minimal toolkits. They don't have 10 different smoothers, or "crowning plates," or other goofy solutions to non-problems, and they don't have elaborate strategies like cambered cap irons that are, again, solutions to non-problems. Richard's approach to the cap iron might seem overly simple to some, but it's not, and it's no accident that he can get more high-quality work done, faster, than just about anyone I've ever seen.

[steven c newman]

Perhaps watching St. Roy and Das Schwarz on an episode of the Woodwright's shop, showing plane basics, would show an easier way? CS simply made a wood pattern of the radius he wanted to grind, and Roy used a hand cranked grinder to grind the bevel. A few figure 8s on the soft and hard arkansas stones, and away they went.
The jig I used is just a pivot point on the tool rest on my grinder. Mainly a point 8" from the grinder's wheel.

to quote from the movie Gettysburg..." George, you do have a way of trivalizing the momentous, and complicating the obvious......ever thought about running for office?"

[david charlesworth]

Mike,

The Plane Perfect kit which replaces the large curved plates with half width ones works.

I have both systems here and much prefer the old one.

I demonstrate this on You Tube. " An interesting method for cambered plane blade sharpening"

Frank Klaus demonstrates the new system on You Tube, titled "sharpening", I think. www.youtube.com/watch?v=pAR9fyXV8go

It is quite helpful to generate the same subtle camber every time.

Best wishes,
David

[Pat Barry]

Missing something here.....
The back of an iron is suppose to be flat. That is where the chipbreaker resides, is on the flat back of the iron. The camber is done by grinding the bevel into an arc, but the iron is still flat.

When the camber, as on a scrub, or jack plane, is in use, the corners are still up inside the body of the plane.....unless you are really hogging the surface off. The main part of the camber is in the center of the iron's edge that is being used. Correct?

Now, most chipbreakers I have seen in the last 6-10 years...have a curved "hump" to them. First thing that is done after the back of an iron is flattened, is to mate that hump part to the flat, without any gaps. Now, IF

one should grind the camber matching curve into a chipbreaker......besides being ugly, it just won't work. The center will contact the iron, right enough, but there will be a large gap to trap shavings at each corner. It will not mate with the iron. Simply because of that curved hump. Plus, any bearing down by the hump (like it is designed to do BTW) is lost except in the center. Corners would be free to just chatter along, trapping all sorts of shavings under the weakened chipbreaker.

About like saving a thick iron would stop all chattering in a cut. Soooo, how do you propose to grind such a curve and still preserve the hump/angle of a chipbreaker? About like this? ( heheheheh....not..
Attachment 341328
This is mine. 2" wide iron, 8" radius camber. Chipbreaker goes right the the corners..
Attachment 341329
The bright silver line? I tend to polish my chipbreakers, so as not to put any drag on shavings
Attachment 341330
Since the jack plane this goes to is a bevel down plane, this is what meets the wood.

There isn't enough of a gap behind the edge to even worry about, as this sort of edge wasn't designed to make them see-through shavings. This was designed to remove a lot of wood, fairly quickly. The curve is not "perfect" and does not need to be. I went down to the shop, and pulled this cutter right out of the plane, other than cleaning of some dust. This is how it looks. No shavings were stuck under the chipbreaker. i might have had to sharpen this iron twice in the last several years of use.

For a smoothing plane, or a minor camber, cambering the chipbreaker to match would be no issue, of course, this is only a few mils across the entire width. Certainly, cambering a Stanley style chipbreaker for a large camber makes no sense whatsoever. It may be possible for other double iron designs, I just don't know for a fact. Why though?

[Brian Holcombe]

The cap iron on my heavily radiused edge jack plane is straight.

I've seen radiused cap irons on Japanese molding planes and have used an inside radius on a Japanese round-over plane. They're taking even, thin shavings that are the length of the radius (minus the extreme edges). A jack plane functions much differently, taking a heavy cut in the center that tapers out to a lighter cut. It makes sense (to me) to use a straight cap iron on a jack plane because you are setting it for a given depth of cut. In the center of the cut, for instance, maybe it protrudes .010" and the cap iron has to be looser than .010" or it will not cut. I have never measured the cap iron setting on my jack plane, it's not that close but just close enough.

[Patrick Chase]

Well, I certainly have tried what you describe. I generally don't write about things I haven't tried, and I have tried most things when it comes to cap irons. There is simple physics here: you can't take a cut that is as deep as the distance from cutter to cap iron. If the cap iron is set .005 from the edge, you can't pull an .005 shaving. If you try to, the cap iron will be below the sole and the plane will not cut. I believe you when you say you are taking "a hogging cut," but I bet the cap iron is not set nearly as close as you think it is.

Nit: The minimum practical setback for a 5-mil cut is more like 0.005/sin(bed_angle). Cap-iron setback is measured along the blade, but but depth is measured perpendicular to the sole...

I don't really know what to make of all this. You keep asserting that there are all these benefits to a cambered cap iron, without any evidence or details. But as far as "hogging" vs. "bringing the cap iron in close" goes, you can do that just as well--better actually--with a straight cap iron. Let's say you have 1/16" of camber and you want to set the cap iron 1/32" from the edge (at the center, where the cut is deepest). No problem, you just hang the corners of the cap iron past the cutter. This will work fine, as long as your depth of cut doesn't exceed 1/32". No, it will not damage the cutter. If you cambered the cap iron, it wouldn't change things one iota; your max. depth of cut would be exactly the same.

The best thing that can be said about cambering the cap iron is that it's a waste of time that doesn't improve performance. The worst thing that can be said about it is that you can permanently screw up a nice cap iron. I argued about this with Dave Weaver a couple years ago. Then I went and carefully cambered a cap iron on a jack, and spent a lot of time playing with it. He was right; I was wrong. You are late to the party.

I think the bit about screwing up the cap iron is key here. The thing that people seem to miss is that the underside of the leading edge of the cap iron is relieved by a few degrees. There is physically no way to camber the leading edge of such a cap iron so that it follows blade camber without *also* causing the corners of the cap iron to lift away from the blade, creating a shaving trap. That relief angle is about 5X as steep as a typical "ruler trick" back bevel, so we're starting to talk about real gaps here.

This is an absurdly simple concept based on high-school geometry, but it seems to be almost completely missing from the discussion.

In principle you could grind out that relief, but you'd have to be super careful to do so at the mating angle (i.e. at the angle at which the cap iron actually meets the blade surface when tensioned) and that would be very difficult indeed.

[Patrick Chase]

Nit: The minimum practical setback for a 5-mil cut is more like 0.005/sin(bed_angle). Cap-iron setback is measured along the blade, but but depth is measured perpendicular to the sole...

An additional thought: It actually is possible in certain circumstances to plane effectlvely with the cap iron set below the sole (and the surface of the wood). For evidence look no further than the Kato/Kawai video. Their "golden" configuration was a 40 deg blade making a 0.1 mm (4-mil) cut with the cap iron set back 0.1 mm (4 mils) along the blade. The cap iron was therefore ~1.5 mils below the surface of the wood, and you can actually see that in the video.

The catch is that in Real Planes (tm) the cap iron isn't exactly as wide as and doesn't line up perfectly with the blade edges. You therefore have to choose between overlap and underlap (or both, one on each side, if you're not careful). If you choose overlap, which is how every production plane I've ever seen comes, then as you say you can't have the cap iron extend below the sole.

Kato and Kawai were effectively edge-jointing (the blade and cap iron were wider than the wood) which is why they didn't face that constraint.

[Jim Koepke]

then as you say you can't have the cap iron extend below the sole.

It might be necessary to file the mouth a bit wider so the hump doesn't bump into the front of the mouth.

jtk

[Steve Voigt]

I think the bit about screwing up the cap iron is key here. The thing that people seem to miss is that the underside of the leading edge of the cap iron is relieved by a few degrees. There is physically no way to camber the leading edge of such a cap iron so that it follows blade camber without *also* causing the corners of the cap iron to lift away from the blade, creating a shaving trap. That relief angle is about 5X as steep as a typical "ruler trick" back bevel, so we're starting to talk about real gaps here.

This is an absurdly simple concept based on high-school geometry, but it seems to be almost completely missing from the discussion.

In principle you could grind out that relief, but you'd have to be super careful to do so at the mating angle (i.e. at the angle at which the cap iron actually meets the blade surface when tensioned) and that would be very difficult indeed.

OK, my turn to nit pick. 😀
Cap irons are soft steel. If you want to create a camber (again I stress this is a bad idea), you bend the corners down. That's how I did it, and that's how it's done in situations where there is a legitimate reason to do so. For example double iron panel raisers exist, though they are not common. Some convex or concave planes, like gutter planes or stair rail planes, have profiled cap irons. I saw a particularly fine pair of Moseley double iron stair rail planes once. As Brian pointed out, there are other types of profiled cap irons as well. But all of these are designed to cut a finished profile, unlike a jack plane.

But anyway, you have to bend the corners the right amount, then grind a new flat on the underside. You might need a couple iterations of this. It's a pain in the ass for no benefit, and a double pain in the ass after you realize you screwed up and want to fix it.

[Steve Voigt]

The catch is that in Real Planes (tm) the cap iron isn't exactly as wide as and doesn't line up perfectly with the blade edges. You therefore have to choose between overlap and underlap (or both, one on each side, if you're not careful). If you choose overlap, which is how every production plane I've ever seen comes, then as you say you can't have the cap iron extend below the sole.

Kato and Kawai were effectively edge-jointing (the blade and cap iron were wider than the wood) which is why they didn't face that constraint.

Sadly, I live in the world of Real Planes. 😂

[Patrick Chase]

OK, my turn to nit pick. 
Cap irons are soft steel. If you want to create a camber (again I stress this is a bad idea), you bend the corners down. That's how I did it, and that's how it's done in situations where there is a legitimate reason to do so. For example double iron panel raisers exist, though they are not common. Some convex or concave planes, like gutter planes or stair rail planes, have profiled cap irons. I saw a particularly fine pair of Moseley double iron stair rail planes once. As Brian pointed out, there are other types of profiled cap irons as well. But all of these are designed to cut a finished profile, unlike a jack plane.

Good luck doing that with the cap irons that ship on L-N, LV Custom, or WR planes. They're basically solid hunks of tool steel (A2 in LV's case), hardness not specified. I agree that that would work on the good old "hump back" type though.

[Mike Holbrook]

Actually my OP was made because I was planing to modify the edges of the chip breakers on some LV chip breakers (C/Bs). The main reason I was planing to modify those edges is the slope of the bevel on the C/Bs is less than the 30 degree bevel on the plane blades themselves. I have read that a higher slope, where the shaving meets the C/B, helps shavings to clear the plane. I was just pondering whether there might be other modifications I might want to do at the same time?

I have read a few different opinions concerning exactly: where, at what angle and for how far the C/B might best be modified. In "real life" all my existing C/Bs are set the same way Steve and Brian set theirs. The LV C/Bs have a small raised area under their edges extending for about 1/4", so they are significantly different than Stanley C/Bs.