Grind the Iron & Fit the Chipbreaker: Part 3

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When I fixed up my first jack plane in the 1990s, I took the advice of every decent person around me: I replaced its old iron with a new Hock blade.

The replacement blade cost almost three times what I paid for the plane, but I didn’t think I had a choice. That’s just what I was told to do.

The Hock blade worked brilliantly, and it’s still at work in a jack plane in Florida. But now I know a little better. Replacement irons and chipbreakers are best for planes that are regularly pushed to the absolute limits of their performance – mostly smoothing planes and block planes.

The jack plane, on the other hand, works just fine with a stock blade – as long as the blade hasn’t been abused too badly by rust or softened by aggressive grinding. Stanley Works (and its competitors) knew how to make good steel. So an old iron that hasn’t been mistreated will take a fine edge and keep it for a good long while.

Even if you do intend to replace the blade in your jack plane to help support modern toolmakers (and I salute you), I encourage you to practice the grinding and lapping steps on your old iron. You’ll learn a lot, you won’t trash your new blade and you’ll have a backup blade for a rainy day.

Dressing the Flat Back
Based on the archaeological evidence, most of our ancestors didn’t care much about flattening and polishing the flat back of the blade. Many old tools show little or no attention to the back of the blade.

Despite this strong evidence, I still flatten the back. But I don’t go nuts. For the most part, I am trying to get rid of the grime, surface corrosion and small rust pits that are common on garage-dwelling planes.

I do this operation with the same setup I use to dress the sole of my planes: a 36” section of granite threshold with some #80-grit belt sander paper stuck to it. Dress the back of the blade until you see clean metal up at the cutting edge. Keep the blade flat against the paper (attaching a magnetic base to the iron is a good idea) and clean the metal filings off the paper after every 30 seconds of work.

This process shouldn’t take long. The goal is to get the blade clean enough and flat enough so that you can polish a small back bevel on the flat face (for this I will use David Charlesworth’s “Ruler Trick” and will cover the technique later in this entry).

After you clean the back with #80 grit, repeat the process with #100, #120 or whatever you have. Just try to make it flat, clean and a little more polished than it was during your earlier steps. I usually end this work on a coarse diamond plate. Some people end it on a #1,000 waterstone. It’s your call.

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Shape the Bevel
The cutting edge of a jack plane should be curved across its width. This is a historical approach that goes back to the very first English-language writing on woodworking in the 17th century. And it’s an approach that holds up today.

How much curve? Of course, it depends. I like a curve that is somewhere between an 8” and 10” radius. The 8” radius is more aggressive, but can be tricky to sharpen in some honing guides (if you use a honing guide as I do).

The 10” radius is easy to do and works with most honing guides. If you want to play it safe, use 10”. If you want to take a small gamble (which is easily undone) then use 8”. Either way, take a scrap of plywood or scrap wood and rip it to 2”, which is the typical width of a jack plane’s blade.

Use your compass to strike an 8” or 10” arc across the end of the wooden bit. Saw, rasp, sand or otherwise shape the end to that line. Then use your template to mark the arc on the end of your plane iron. Use a fine fine fine Sharpie to make this mark. And make it as close as you can to the tip of the iron. Now it’s time to grind it.

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Grind the Bevel
Grinding is not hard. The idea of grinding is what’s hard. Get a grinder – fast speed, slow speed, hand-cranked, whatever (I have a fast electric one). Put a coarse wheel on it, like an #80 wheel. I use Norton 3X wheels because they seem to cut cool and fast. But I’ve worked on wheels of all colors. Coarse wheels that are friable (meaning they break down easily) are way better than dense wheels that don’t break down.

You can do a lot of research on grinding wheels. Or you can skip all that and just work with what came on your grinder and adjust from there. One important detail, however, is to dress the wheel so it has a slight convex camber. This camber makes it easy to maneuver the tool you are grinding.

So here’s what actually is important: the tool rest. Not the type of tool rest – whatever you got is fine – but how it’s set. Set it so it’s 90° to the grinding wheel. Yup, the goal is to grind the tip of your blade at 90°. Grinding the blade this way gets the curve to shape quickly, doesn’t heat up the blade much and gives you some flats at the tip of your blade to gauge your progress when grinding the bevel.

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So grind the tip of the blade flat at 90° and down to your Sharpie line. The blade shouldn’t heat up much during this operation. But let’s talk about heat and steel.

Keep it Cool
When I grind steel, I pause after 5-10 seconds of hard grinding and check the temperature of the blade by pinching it with my fingers. If my fingers involuntarily recoil, the blade needs to be cooled before grinding it more. Dunk it in a cup of water until it cools. Note: This is not quenching (quenching is something else). This simply cools the blade.

If, however, you can grasp the tip of the work and continue on, then continue on. (Side note: If you do overheat the blade and it turns a little blue, it’s not the end of the world. Try using the blade anyway and see if you even notice that the edge degrades too quickly. Grinding away that blued area is usually an invitation to make the problem worse.)

When you get to your Sharpie line, pause to examine the flats on the tip of the blade. They should be the same on either side of the apex of the blade. Fix them if they aren’t equal – tiny equal flats is the first goal.

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Grind the Bevel
Set the tool rest so it grinds at 25°. There are lots of gizmos that will do this. I use a popsicle stick with 25° cut on the end. When I grind the bevel on a jack plane, my first goal is to create a smooth 25° arc on the bevel that acts like a path I can then follow to complete the grinding.

I create this “path” by first touching the center of the iron to the wheel lightly. Then I move the iron right while increasing the pressure against the wheel. I repeat this operation while moving the iron left. I do this a couple times and look at the results. When the arc across the bevel looks even, I can work on removing lots of metal.

This is the part that is “the grind.” It can take a bit of time depending on how messed up the iron is.

During this operation, the motion is like the windshield wipers in your car. Touch the iron lightly to the wheel and shift it left and right – adding some forward pressure at the corners. Do this a couple times and pause to check the temperature of the iron and to see if the tiny flats at the corners are disappearing at the same rate.

If they are, congrats. Carry on. If not, you’ll need to add more pressure on the corner that needs to play catch-up.

Cool the iron in the water when it gets too hot.

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When the flats become tiny – about the width of a hair – you are ready to hone the iron. Try not to remove the flats on the grinder if you can. After the flats are gone, the tip of the iron will heat up rapidly.

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Honing
Hone the iron using the same media you use for your chisels and plane irons. I use a honing guide, which makes the process a snap. Secure the iron in the jaws of the guide and set it for 30° or 35°. I use 35°. This is where you might encounter problems with an 8” radius. On some guides you won’t be able to hone the corners of the iron because the body of the honing guide will hit the stone, denying you access to the corners of the blade. Switch to a 10” radius or sharpen the iron freehand.

Start on your coarse-grit stone (I use a #1,000-grit waterstone). Rock the iron left and right as you roll up and down the stone. Proceed until the flats are gone and you have created a burr on the backside of the iron. Then proceed up the polishing grits (I use #5,000 and then #8,000) to finish the bevel.

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Remove the burr and polish the backside of the iron. I prop up the iron on a thin steel ruler (thanks David Charlesworth) so I only have to polish a tiny bit of metal at the tip. The first time you do this on an iron, it might take a minute or so, but that beats the heck out of the hours it would take if you had to polish the entire backside.

The Chipbreaker (aka Cap Iron)
Luckily the chipbreaker isn’t as critical to a jack plane as it is to a smoothing plane. It’s primary job in a jack plane is to attach the iron to the blade-adjustment mechanism in the frog. Plus, the hump of the chipbreaker helps deflect shavings up and out.

Still, you need to make sure that you don’t create a “shavings trap.” That happens when there’s a gap between the iron and breaker that is big enough for shavings to get into. Stone or file the underside of the breaker until you get a good light-tight fit between the breaker and iron.

One of the most common problems with old breakers is that they have flattened out a bit during the last 100 years and you need to restore their “spring.” To do this, clamp one-third of one end of the breaker in a vise and press gently but firmly against the un-clamped portion. You only need a tiny tiny bit of bend to fix the problem. It’s easy to over-do it. It’s also easy to undo it.

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If you can’t get the breaker working no matter what you do, consider buying an aftermarket one from Hock Tools or Lee Valley. That will fix your wagon.

Now you can assemble the whole plane and make some shavings. Attach the chipbreaker so it is behind the curve of the iron, but don’t position it too far back – that can give you troubles. You can make it so that you cannot retract the iron into the mouth of the tool. Tighten the breaker snugly. Check the frog screws again to make sure they aren’t loose (I’ve done this).

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And assemble the plane. Yay.

In the next entry, I’ll show you how to make a board flat with a jack plane.

— Christopher Schwarz

The Jack Plane Series
The Jack Plane You Really Need: Part 1

Clean & True Critical Surfaces: Part 2

Grind the Iron & Fit the Chipbreaker: Part 3

Set Up & Use: Part 4

About Lost Art Press

Publisher of woodworking books and videos specializing in hand tool techniques.
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31 Responses to Grind the Iron & Fit the Chipbreaker: Part 3

  1. Andy says:

    Is a secondary/micro bevel useful on a jack plane? I’ve been using a 25 degree primary, and 30 degree secondary.

    Also, if you have any brand name recommendations for a hand cranked grinder, I’d be grateful. The second hand market can be overwhelming.

    Thanks for all of this.

    Like

    • I almost always use a secondary bevel. Why sharpen steel that doesn’t touch wood?

      Like

    • And I’m no expert on hand cranked grinders. I bought one at a Mid-West Tool Collectors meeting.

      Like

    • freonguy says:

      Andy:
      I have refurbished several HCGs. The biggest issue is the shafts are often bent because things were handled poorly.
      Also, the arbors are often 3/8”, which is problematic with the bushings supplied with most wheels.
      Make sure that there is enough clearance for a 6” ( or larger ) wheel
      Hopefully you can turn one over before you buy. That being said, I have seen several EBay purchases that have been very nice, some not so much.
      I have attended a WW School that uses HCGs exclusively: once you get used to them, it is a soothing process.
      Good Luck!

      Like

      • Andy says:

        Thank you both! I appreciate the replies.

        The Pike Manufacturing grinders (Handy Andy) I’ve found on eBay look promising, but pricey. I’ve heard that while they often have 4 inch wheels they can usually accommodate a 6 inch wheel without issue. Not sure if that’s true, as I rarely find any in the wild.

        Like

  2. Steve C says:

    Excellent post

    Like

  3. Greg says:

    Outstanding! A really swell article.

    Like

  4. So I’m guessing my 6″ radius on my Jack and smoother is just bat crap crazy…

    Like

  5. John Cadd says:

    Here is a nice way to achieve a super smooth curve across your plane blade. I use a honing guide with a roller but I drilled through the sides and fitted two wheels (Meccano wheels about one inch diameter ) to make a wider support. The honing guide is now used Upside Down .That`s the first position . Level tracks either side of the sharpening stone or plate support the wheels. Next is the crafty part. The stone or plate is normally kept level with the side tracks but if you fit two thick shavings under 2 diagonal corners the plate will rock to and fro as you sharpen the blade. This gives a lovely even curve along the edge ..So just two thick shavings. One front left and the other back right. and away you go .Forget the grinder .

    Like

    • John Cadd says:

      I should add something here .The honing guide needed two small triangular plates screwed to each side ..Two screws each side to hold it on and a hole in each plate for the roller axle. I used an oil stone for this today and it works a treat .I forgot how good it was .The “shavings had been upgraded to small pieces of cork Remeber , the curve is reproducable each time I use this method . Nothing needs to be reset or adjusted .
      Strangely I imagined it all before it was made. Normally I discover new things almost by accident .

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  6. Mattias Hallin says:

    I don’t have a grinder, so in order to put a camber on those plane blades where I want one, I’ve adopted (and adapted) a technique mentioned by David Charlesworth in his video on plane sharpening as something suggested to him by one of his students.

    What he does when re-sharpening a cambered blade in that video is to take a strip of thin plastic (from an old plastic binder, he says) that is about five thou thick, and lay this first on one edge and then the other of a series of waterstones. One edge of the blade (which is held in a honing guide) is then allowed to ride on the strip while the opposite edge is pressed firmly on to the stone by the fingertips. The fingers are then moved halfway in towards the centre and finally the centre is worked without the strip.

    Basically, this is of course the same technique as just changing the point of pressure with the aid of the fingers, but made a bit more predictable by the addition of a (very simple) jig.

    At the end of the segment in question, David Charlesworth then says something to the effect of “now, if I could only find a strip of plastic twice as thick, I could make this method even more precise” (not his exact words, but I don’t have the video to hand at the moment). This got me thinking, and as one of my other hobbies is model boats, I had a stash of plasticard sheets lying around, including some that was respectively five, ten and 15 thou thick. From these I cut a strip each, maybe 3/4″ wide or so (and slightly longer than the stones).

    For my jack plane blade, where I wanted the most pronounced camber, I first set the blade up in the honing guide for the 25° primary bevel angle, and then used these three thicknesses in sequence on a series of stones (extra-extra-coarse through to coarse diamond stone to grind, followed by 1000, 3000 and 8000 grit waterstones to polish) together with seven positions of finger pressure (centre and three to each side), until I had a primary bevel with the desired camber (and that was already pretty sharp in itself).

    I then simply reset the blade in the honing guide to a secondary bevel of 35°, and honed that with a few strokes in each of the seven positions (using the strips and fingers in the same sequence) on the 1000 and 8000 waterstone. Bob. Uncle.

    I haven’t measured the exact radius, but as an eyeball estimate, I’d say it’s probably not that far off from a 10″ radius. On my smoother, where I wanted a fairly light camber, I just used the five thou strip, while for the jointer I used five and ten thou strips.

    Probably not as simple or as fast or as good as using a grinder — but much faster than waiting until a grinder eventually makes it way to my workshop, and more reliably repeatable than just using freehand pressure … And the advantage of the plasticard, compared with e.g. an old plastic binder, is of course that it comes is a series of known thicknesses and is readily available from any model supply shop at quite reasonable prices for the quantities involved.

    Like

  7. Gav says:

    Hi Chris,
    Having not used a mag clamp before but thought it would be good for this type of flattening work have you found it to be a roaring success or are there any hiccups ? Thanks

    Like

  8. John Cadd says:

    2 days ago I saw a honing guide with two roller bearings either side. It looked very professional .That would be even better than my improvised effort with Meccano wheels .See above post .

    Like

  9. Patrick says:

    Thanks Chris. Good stuff.

    Like

  10. Greg says:

    I prefer grinding on my Tormek. The water cooled stone prevents any burning. It takes a bit longer, though. I gave my regular grinder away.

    Like

  11. Henrik says:

    Great article, however, one point leaves me confused:
    Why should you create a wooden template to strike the curve on the iron before grinding it to shape? Wouldn’t a piece of cardboard or simply paper do it just as well – and take seconds to make (I don’t see the template being used later on in the process but maybe I am just blind?)?

    If you can clarify, much appreciated

    Thanks
    Henrik

    Like

    • You can make one out of plastic, cardboard, Masonite, whatever. I use wood because I have tons of scraps of it. I keep the wooden template so I can mark out the shape every time I grind the iron. As you sharpen the iron, the curve will get flatter and flatter, no matter how much you strive to keep the curve intact.

      Like

  12. Vince says:

    One thing I never understood about Stanley planes was the “No” in No. 5? Why not Nm. or Nb? I’m no National Spelling Bee Champion but I’m pretty sure there is no letter “o” in the word “number”.

    Like

  13. josef1henri says:

    Thanks so much, Chris. I really like your common sense approach.

    Like

  14. John Cadd says:

    While making a determined effort to sort out one of my planes today I noticed the pivot pin for thr depth adjuster was coming adrift..That was a new one for me .

    Like

  15. Dean Morrell says:

    Thanks for the tip on persuading the chip breaker. That just saved an old Sargent #4 and my mind.

    Like

  16. John Cadd says:

    One site shows a Japanese series of photos , close ups of a chipbreaker in action . They recomended the edge of the chipbreaker to have an 80 degree angle . My version is also to polish all the edges in the mouth to get rid of any friction . The 80degrees edge is saying –You don`t want a sharp edge on a chipbreaker as that would cut the shaving just right for any tiny gaps to jam them tight .

    Like

  17. bgmillerbrian says:

    Chris is a regular guy with “un-fancy methods for other regular guys. My kind of guy. Get it done and get back to work. Thanks for keeping it simple for us non-pros. Excellent.

    Like

  18. John Cadd says:

    I have seen pictures of Hock chipbreakers which would be an improvement in a wooden plane that used a standard shape chip breaker with a hump at the end . The Hock has a flat top surface and the wedges (one each side } in a wooden plane would be a much better fit. The straight top would allow even pressure right down to the tip .

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