Cap iron for a cambered blade

[Mike Holbrook]

If I want to use cambered blades on most of my planes, but I also want to use chip breakers/cap irons on many of them do I need a specially altered chip breaker?

I get the idea that the camber in the blade makes it hard to get the cap iron close enough to the center of the bade's edge for it to do it's job. Certainly a smaller camber might be easier, but lets assume I want larger cambers too.

The other question being whether I should modify the angle of the edge on the chip breaker while I am at it?

Blum Tools is the only company I am aware of that offers to modify the device holding the plane blade to fit cambered blades.

[Brian Holcombe]

I leave the cap iron straight.

[Tom M King]

For the iron that you need to get the cap really close to the edge on, the camber is so small that the curve doesn't matter for this.

[Jim Koepke]

My plane with the intentionally cambered blade is used as a scrub plane. Setting the cap iron close isn't a worry.

If there is a camber on any of my other planes it is unintentional. This means there isn't an issue with setting the cap iron close.

jtk

[david charlesworth]

It is quite easy to camber a C/B edge. I hold it in an Eclipse type honing guide which will allow 45 degrees.

It is then cambered in the same way as a blade edge.

This allows ultra close C/B setting, if you wish.

Best wishes,
David

[Steve Voigt]

I leave the cap iron straight.

This is the right way to do it. I understand the desire to camber the cap iron, but it rests on a fundamental misunderstanding of the relationship between cap iron distance and depth of cut.

Simply put, the deeper the cut, the farther back the cap iron needs to be. If you are taking an .002" shaving, the cap iron can be extremely close, as close as say .004" from the edge. But if you try to take an .004 shaving with the same setup, the plane will not cut at all, the cap iron will just drag across the wood.

However, if you use a cambered cutting iron and a straight cap iron, the setup is self-regulating. Where the cut is deepest, the cap iron will be furthest from the edge, and vise-versa.

Richard Maguire has a good explanation of this is one of his cap iron videos. He uses camber on every cutting iron, and to determine cap iron distance, he simply sets the corners of the cap iron flush (or nearly) with the corners of the cutting iron. So for his smoother, which has only a few thou of camber, the setting is extremely close; for the try plane, which has slightly more camber, the setting is slightly greater, and so on.

[Mike Holbrook]

Interesting responses. So far I have not modified a chip breaker either Brian. I think Steve makes a good argument for not doing it as well. Thanks for your idea David.

I have been thinking about modifying the angle of a chip breaker's edge because I have read that there is an optimal angle that causes the shaving the plane makes to bend and break optimally. I was thinking about modifying the camber at the same time to see what that would do. I am wondering about the different thickness of the shaving a cambered blade makes too. The cambered blade may present the shaving differently to the chip breaker.

[Patrick Chase]

If I want to use cambered blades on most of my planes, but I also want to use chip breakers/cap irons on many of them do I need a specially altered cap iron?

I get the idea that the camber in the blade makes it hard to get the cap iron close enough to the center of the bade's edge for it to do it's job. Certainly a smaller camber might be easier, but lets assume I want larger cambers too.

The other question being whether I should modify the angle of the edge on the cap iron while I am at it?

Blum Tools is the only company I am aware of that offers to modify the device holding the plane blade to fit cambered blades.

Leave it straight.

For smoothers and jointers you typically only use a few mils of camber, and that won't interfere with the cap iron.

Also, the bottom of the cap iron's leading edge is undercut by a few deg, so putting camber on it will unavoidably "lift" the corners and compromise mating. In this case the cure would be worse than the disease.

[Charles Guest]

"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.

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.

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.

[Jim Koepke]

Maybe something is getting by me here.

If a smoothing plane's blade has ~0.002 - 0.005" of camber why does the cap iron need be cambered? Will the blade be set to take full width shavings?

My cap irons are of two types; the originals and the ones purchased with Hock blades.

Both of these types have a very small area of cap iron interfacing with the blade. On my Stanley cap irons if the cap iron is ground to match my scrub plane blade's camber there will be a big gap between the iron and the blade at the edges. It doesn't seem the Hock cap irons would have much of a better fate. Most likely a lot of time would be wasted picking shavings out of the cap iron.

Anybody with a very close cap iron setting on their smoother can walk out to their shop and taking a hogging cut. Try it. It's a bit of a hard(er) push but that's about it.

For me it is harder to push because doing this causes the shaving to choke up the works. Maybe if the mouth of the plane was filed wider. My planes are usually set up for a single purpose. Some can do more than one thing. It isn't my style to try and use one plane for every job in the shop. My scrub plane doesn't do smoothing, my smoother isn't a good jointer and my jointer isn't a good jack. My most versatile planes are my #5s & #6s. They can do jointing to smoothing within their own ranges.

jtk

[Charles Guest]

An essentially straight smoother cutter doesn't need a cambered cap iron or very much of one mostly because the cutter isn't cambered to any real degree, although the very light pressure it takes to produce a little curve on a cutter takes even less on the soft steel of the cap iron. A mere suggestion of pressure on the cap iron and she's cambered enough to match the smoother cambers mentioned in the other responses, if you choose to do this. Tidying up the mating surface takes about the same amount of time and light pressure but of course is done after the desired amount of curve is introduced.

A very close set cap iron needs a bit of a wider mouth to prevent clogging for all but the whispiest bit of material removal.

[steven c newman]

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..
IMAG0004.jpg
This is mine. 2" wide iron, 8" radius camber. Chipbreaker goes right the the corners..
IMAG0003.jpg
The bright silver line? I tend to polish my chipbreakers, so as not to put any drag on shavings
IMAG0002.jpg
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.

[Mike Holbrook]

Charles mentions one of the challenges I have been facing in my attempt to maintain cambered plane blades. It can be a challenge to maintain the camber at a fixed curve. I tend to use a little more curve at the corners which makes things a little more interesting.

I was specifically thinking about Lee Valley/Veritas chip breakers for double iron blades. The chip breakers for these planes have a raised area on the bottom of the chip breaker, which is about 1/4" wide. When I tighten one of these up most or all of the chip breakers bottom edge registers against the blade. This is a larger registering area than Stanley planes tend to have, as Jim mentions. This wider registering area may give me a little more area to work with, or the C/B may just not register correctly once modified. Not sure exactly why LV makes their C/Bs this way but I am guessing Rob Lee and co. had their reasons.

A number of years back Toshio Odate came out with his Odate Crowning plate, which was designed to make a fixed predictable camber on plane blades. I almost bought one to try it out at Highland Woodworking. Apparently the source for some of the materials used to make these went away. Highland apparently stopped carrying them. I was curious and did a search for Odate Plate. I found "PlanePerfect.com LLC" which apparently makes or carries the "next generation" Odate system for cambering plane blades. Which got my mind working on this topic again. I am still trying to figure out how this system works...

This cambering system which utilizes half wide dressing plates and a jig for holding them in place, is reported to work on plane blades, chisels.... If nothing else this is an interesting combination of traditional Japanese and western tool sharpening strategies.

[Mike Holbrook]

I should say I just received a copy of a DVD "Talking Japanese Tools" with Toshio Odate. Which is what got me thinking about Odate's thoughts about sharpening again.

[Paul Sidener]

This might help.