Chris Schwarz's Blog

Camber With a Honing Guide

A curved cutting edge is critical to most operations with your bench planes. The curve prevents the corners of the iron from digging into your work, and it allows you to correct the flatness of the face or edge of a board.

But how do you create this curve, sometimes called a “camber?” And how do you create it with a honing guide, which seems to encourage a cutter that is sharpened straight across?

There are lots of valid ways to create the curve. Here’s how I do it. My method has the provenance of a stray dog , a little David Charlesworth, a little Robert Wearing, and a little bit from everyone else who has ever taught me sharpening.

I start with the #1,000-grit waterstone. This stone cuts quickly enough to shape an edge or remove small nicks or chips. Clamp your cutter in your honing guide then (mentally) divide its edge into five “positions” (see the photo above for details).

The trick to creating a curve is to put finger pressure at each position. At position “1,” put your fingers firmly against the corner and sharpen the corner for 10 strokes.

Then move your fingers to the other corner (position “2”) and go for another 10 strokes. Then, at positions “3” and “4,” go for seven strokes. Then do a few strokes in the center at position “5.” Now check your work with a square.

You need to learn what the curve should look like for each of your planes. Here are the basic principles: If the iron is bedded at a high angle greater than 45�°, you need less curve. If the iron is bedded at a lower angle such as 12�° or 20�°, you need more curvature to get the same effect.

And what is the desired effect? You want to take the widest shaving possible without the corners of the cutter digging in. There is math here. Having a .005″ arc-to-chord curve at 45Ã?° results in a curve of .0035″ being exposed out of the mouth. (If you have a bevel-up plane bedded at 12Ã?°, the same .005″ arc-to-chord curve will result in .001″ curve being exposed in the mouth , thanks to woodworker Rob Porcaro for the formula.)

The honest truth is you just need to learn what the right curve looks like when you show the cutting edge to a straight edge. If there is too much curve, sharpen some more in the middle position (5) to flatten the curve. If the curve is too flat, add more finger pressure or strokes at the corners to increase the curvature.

When you have a satisfactory curve, advance to the polishing grits (#4,000 then #8,000) and repeat the same regimen. The polishing grits will remove less metal, but you definitely can increase or decrease the curvature while polishing.

It takes a little practice to find the right curvature for your plane, but the rewards are enormous: Shimmering handplaned surfaces with a sensuous, scalloped and touchable texture. It’s worth the effort.

– Christopher Schwarz

15 thoughts on “Camber With a Honing Guide

  1. edf

    Chris- feel free to ignore my question as I just noticed the links you gave in an earlier comment. Those links are broken but I was able to find the articles and they answered the questions. Here are the new links if you want to update this thread. Thanks again. -Ed

    http://www.popularwoodworking.com/woodworking-blogs/chris-schwarz-blog/sharpen-a-fore-plane

    http://www.popularwoodworking.com/woodworking-blogs/chris-schwarz-blog/tips-on-fore-planes-and-flattening-panels

  2. edf

    Chris- Would you say a few words about setting up a camber for a jack plane, i.e., 1/16″ camber? Do you establish it on a grinder? Having established it, can you use the “rocking eclipse guide” trick to hone it? I learned the moving pressure trick for getting a gentle camber from David C’s excellent videos, but can’t imagine hogging off an 8″ radius for a jack that way. And, having fallen under David’s spell, I can’t sharpen by hand very well, so am hoping honing at least will work with a guide! Thanks for any insights. I’m trying to put into practice what you showed in your Coarse, Medium, Fine DVD. -Ed

  3. david charlesworth

    ocd,

    So glad you enjoy the books.

    Yes I work on the c/b’s of St. Thomas as well. Chris seems to solve the problem by setting well back from the edge.

    If you wish to set real close the top surface matters as well as the fit. Polish may not be essential but sharp 45 deg edge does. Blunt edges cause choking.

    best wishes,
    David

  4. ocd

    This query is for David Charlesworth. First, I love your three books on wooodworking, the set, that is. If you’ve written more, I haven’t seen them.

    Are you including Saint Thomas Lie-Nielsen is the "major manufacturers" whose C/B is not good to go out of the box?

    I probably need to have some more espresso, but I have trouble understanding your post about the polishing the C/B. Isn’t it enough that it be straight and smooth, having full contact with the back of the iron?

    Thanks, ocd

  5. Tony

    Chris,

    Do you use a scrub plane, which would normally use an even more pronounced camber? I think Rob Cosman uses it in his Rough to Ready video to thickness boards.

    Tony

  6. Christopher Schwarz

    Dave,

    Your question is a can of worms — just search some of the Internet forums to get a clear picture of the debate.

    Here’s how I sharpen the planes:

    Smoothing plane: Just a slight camber to keep the corners from digging in.
    Jointer plane: A little stronger camber so that I can use that to correct edges that are out of square.
    Fore plane: A pronounced camber (an 8" radius) so that I can hog off material by working across or diagonal to the grain.

    Chris

  7. David Brown

    Thanks for the post on cambering, which I’ve been thinking about lately. My question is simply do you camber the blades of all of your bench planes? I know it’s the norm for smooth planes, but I thought there was some argument for straight blades for jointer planes. I’m not sure what’s usual for fore planes. Although it doesn’t take that long to sharpen a cambered blade, it does take a bit longer than a straight blade, so I’m struggling with the why camber question on jointer planes, since any plane tracks will be removed when you smooth plane it later.

    Thanks for any advice.

  8. Narayan

    I start with the Odate stone you recommended, which quickly gives me a great (and centered) starting point. I then follow up on the waterstones, adding or removing camber as the plane/work dictates.

  9. david charlesworth

    Chris,

    I have to agree with Wesley. A similarly cambered cap iron or chipbreaker allows one to set the edge of the C/B very close to the edge of the iron.

    I was minded to write before when you said that setting the C/B back was a good way to avoid choking. I’m sure it is, but it does not adress the fundamental cause of choking, which is a badly prepared C/B edge.

    I know of no major manufactirer who supplies a properly prepared chipbreaker edge.

    The fit to the back of the blade must be good and the top surface should be well polished at not more than 45 degrees to the back of the blade. ( lower angles must be used with high angled frogs if the mouth is set very fine.)

    This work on the cap iron is quite difficult and needs precision. I routinely set mine as close as possible to the blade edge for fine finishing, maybe as little as 12 thou".
    best wishes,
    David Charlesworth

  10. Rob Porcaro

    Lest I seem like too much of a nerd, the formula which you have kindly cited, Chris, is just meant to quantify and guide one’s intuition. I never actually measure the camber and agree that it is really a matter of getting to know what "looks right". Above all, monitoring the feedback from the plane’s performance is the best guide to what’s right.

    I’ve heard of Japanese craftsman cambering the chipbreaker edge. I sure don’t.

    OK, I did measure the camber, but just once, I swear.

    Rob

  11. Christopher Schwarz

    Reed,

    It works with both. I flat grind sometimes and hollow grind other times (depending on the machine that is closest).

    It’s really the secondary bevel that matters — the steel in the middle doesn’t need to be sharpened.

    Chris

  12. Reed Robinson

    Excellent treatment of one of those nuances of getting into planing which is so often under-explained in the "plane-like-a-pro"-type articles aimed at new handtool users.

    A couple quick questions though: First, how well would this work on an iron that had not been hollow-ground. I wasted an entire year polishing the entire bevel because I was afraid of screwing up a hollow-grind attempt. Now that I finally forced myself to learn it the sharpening of the bevel goes SO much faster. I love the Charlesworth DVDs, but I don’t think he emphasized the importance of hollow-grinding enough. I had a very, very hard time raising a frech wire edge before preHG, let alone creating a camber.

    Granted, 95% of your faithful blog followers already know this, but for the 5% who don’t realise it’s importance, it may be worth mentioning. Like I said, I spent an entire year toiling in the dark ages of sharpening (despite religiously reading your blog).

    As always, thanks for the great work.

  13. Christopher Schwarz

    Wesley,

    I don’t camber the chipbreaker because I don’t set it as close as some woodworkers. I usually set it 1/16" to 3/32" from the cutting edge, which diminishes clogging in my experience.

    As far as replacement breakers, but the Lie-Nielsen and Hock are vast improvements over the old Stanley ones. I own both and use both. I don’t have a preference, really.

    Chris

  14. Wesley B. Tanner

    A nice, crisp description. Why don’t you follow this up with preparing the cap iron for the cambered iron? How much curve do you need to have the chip break and exit? Additionally a comparison of Lie Nielsen and other replacement cap irons would be interesting.

    Thanks,

    Wesley

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