Chris Schwarz's Blog

Sharpening: Here's What I See

I’m fairly well convinced that my ears are different than yours. The music I like isn’t going to sound the same to you. It’s almost impossible for me to share with another person what the Heartless Bastards sounds like to me. Language is too imprecise.

Same goes with the eyes (and tastebuds). How you experience a Paul Klee or a Hebrew National is impossible to share with me.

The problem is that our senses are tied to our big, dumb brains, which process and filter the waves of information our organs receive.

And so it makes me crazy to explain how to sharpen to people because it involves so many senses (except taste I think) that are processed. And there is so much information that comes in through our eyes, fingers and ears that beginners cannot focus on what is important.

So here is what I see when I sharpen a plane iron. I’m going to show what it looks like on the unbeveled side, which I call the “face” and others call the “back.”

Above is what the face of a smoothing plane iron looks like when it is fresh from the wrapper. The vertical scratches are deep and are left behind by the manufacturing process. These have to be removed. So I begin by abrading the tool on my #1,000-grit waterstone.

After a short time on the #1,000-grit stone the metal gets a scratch pattern that looks like this. I move the iron back and forth diagonally on the stone and examine it every couple minutes. I’m looking for where the deep vertical scratches go all the way to the end of the iron. That’s where the metal is weakest and the edge will begin to break down. The arrows point to where I see problem scratches. When these scratches disappear at the end of the iron, I can move on to the next grit , #4,000 grit.

Usually #4,000-grit stones start to give me a good polish. And so the #1,000-mesh pattern is generally replaced by more of a polish. Some #4,000-grit stones don’t do much polishing, but most do. Try working the iron in one direction , this brings up the polish faster.

If I can see the deep vertical scratches, I might need to drop back to the #1,000 grit. In the drawing above you can see some #1,000-grit scratches and one deep manufacturing scratch at the right that are problems. Usually I’ll drop back to the #1,000-grit stone here for a few minutes to get that deep scratch out.

I’ll also start to see faint horizontal scratches left behind by the #4,000-grit stone. When the #1,000-grit scratches and manufacturing scratches are gone, move to your next stone. For me, that’s the #8,000-grit waterstone.

This stone should bring up a nice mirror-like polish. You might have some horizontal scratches from this stone, but those generally aren’t a problem. Look for any #1,000-grit diagonal scratches (as shown with an arrow above). Keep working until all the vertical and diagonal scratch marks are polished away right at the cutting edge. Don’t worry about the scratches that don’t make it to the edge.

I’m sure all this looks different to other experienced sharpeners, but these crude pencil drawings are about as well as I can explain it without coming to your house.

– Christopher Schwarz

22 thoughts on “Sharpening: Here's What I See

  1. Frankie Talarico

    this is the same way many pros sharpen tooling. There is also the flat glass technique. I like this post much better because you can illustrate on the tool itself to show your progress. It’s kind of like spraying black dots on your clear coat finish as a for of measure, it eliminates burn though, or in this case under sharpening.

    Always a fan, nice post.

  2. Glen

    Great explanation that makes sense.

    I guess my high school shop teacher left a few details out when he said, "When the grinding wheel starts to turn the edge of the plane iron (or chisel) blue, it’s sharp enough."

    Thanks for sharing, Chris.

  3. Eric

    If this doesn’t explain it succinctly, nothing will.
    Good job Chris & keep up the good work.

  4. Carl Stammerjohn

    Great description and drawings. It seems just about impossible to photograph what you drew, so the drawings are great.

    I try to make sure the big scratches end at least 1/4" away from the edge, and preferably 1/2". My assumption is that unless you do that, there may be some portion that isn’t visible to the naked eye that sneaks its way to the edge.

    In the back of my mind resides the electron microscope pics from Leonard Lee’s sharpening book. Those little scratches make a big difference at the edge.

  5. Greg

    "pencil drawings are about as well as I can explain it without coming to your house."……Come on over, I’ll fire up the grill and we can sit on the porch and talk shop.

  6. David

    Chris – There’s a very nice, and very well thought out, explanation of flattening the back of a blade in Toshio Odate’s "Japanese Woodworking Tools". If you have the book, it’s worth reading this section – one of the more eye-opening things he explains is why not just any waterstone is going to work on any blade.

    But one other item I’ve tried, and it works exceptionally well, is to use his "flattening stick" – one cuts a piece of hardwood slightly (and only slightly) narrower than the blade to be flattened, then one lays the stick on the bevel side of the iron, with the end extending 4 or 5 inches beyond the iron’s edge. By using a two handed grip on the blade/stick and the end of the stick that extends past the blade, one has a very nice way to extend even pressure all the way across the width of the iron.

    One advantage to this method is that it avoids the potential pitfall of the magnet trick – if you’re flattening a relatively thin blade, such as from a molding plane or an antique stanley, the force of the magnetic attraction can actually distort the blade. Only very slightly, but enough to see when one laps on a honing stone.

  7. Samson

    If I’m remembering correctly you have kids, so you might understand this reference. Did you ever see the one where SpongeBob teaches Patrick to open the jar?

    In case you missed that one, what i’m trying to say is that it’s easy to forget what’s not obvious when you’re starting out. You’re a good teacher.

  8. Richard Dawson

    It seems like every time Chris posts anything that relates to some of the basics of woodworking, my reaction is that this is the clearest, most informative, to the point article-ette I’ve seen in a long time. I’m almost to the point of not saying anything because I’d be too busy heaping praise on him. Great post, great discussion; I’m learning a lot.

    John, I think the answers are that 1) the real critical areas are on business ends for both chisels and planes, and 2) horizontal strokes aren’t used for small chisels. David Charlesworth talks about these points in several DVDs, and Chris can explain it better than I can.

  9. John Contract

    Chris, thanks for this. Do the same rules apply for chisels as well? Are we only concerned with a mirror polish close to the edge? or, is a mirror finish more important on a chisel because there is typically more contact with your work. Also, I’d really like it if you could offer some advice on flattening smaller chisels (1/4") or less when horizontal strokes are not really advisable. Perhaps in a future post?

  10. Eric

    Wow, Chris, what a great post. I’ve popped all my plane blades in several padded envelopes, and they should get to you shortly. Thanks in advance – I’m sure you’re not too busy. ;^)

    While it’s true that you only really need the 1/8" ( or 3mm) or so above the edge to be shiny and flat, it seems that while you’re taking the effort to do all this, you might as well do it as far up as you can. If you can get 1" or 2" dead flat, you won’t ever have to touch the face for a long, long time, right? Seems worth it to me.

  11. Gye Greene

    Ah; makes sense.

    With the magnetic wall strips, it probably also matters how one removes the tool. As I recall from middle school science class, you magnetize a chunk of ferrous metal by stroking it with a magnet over and over in the same direction, which polarizes the metal. So, if you constantly **slide** the chisel (etc.) off the metal strip — and always mount it in the same orientation — you’ll be doing the same thing, incrementally.

    If you pulled it directly away from the wall, it probably wouldn’t get magnetized. But, that’s an awkward way to remove it.

    –GG

  12. Christopher Schwarz

    It takes a good like while for the blade to become magnetized. And you only need the magnet once — on the initial flattening. So I haven’t seen any problems. The only tools I’ve seen become magnetized were in constant contact for a long while.

    Chris

  13. Gye Greene

    Brilliant.

    Doesn’t the use of a magnet negate your earlier advice (maybe it was in one of the *.pdf files on the "Workshop Things" CD-ROM) to not hang up your tools using magnetic strips — because metal filings cling to your magnetized chisel blades, making them harder to sharpen?

    Haven’t tried it, but it seems like wood glue and a small piece of scrap wood could be glued to the plane blade (if you removed the oil residue) as a temporary knob/handhold — then popped off when you’re done.

    Or, some sort of suction cup?

    –GG

  14. Christopher Schwarz

    Agreed! I have a large (and inexpensive) magnet for dressing flat surfaces. I’ll post a photo soon.

    Chris

  15. Jeremy Kriewaldt

    A very nice description, Chris from which I take three essentials:
    1. All you are flattening is the bit where the edge is going to be made, you are not trying to turn your plane iron into a mirror, just get a mirror finish on that edge (and enough extra for a year or mor of honing).
    2. Use distinct directions for each level of grit, this helps you to see when you have got rid of the scratches from manufacturing (first grit) or previous grit level (subsequent steps.
    3. Move to a higher grit only when the scratches you started this grit level with have disappeared from the edge and back a bit (say 3mm).

    I agree with all of these and would only add:

    4. It is important to keep the iron flat on the grit surface, use a grip that makes that easy for you. In my case, I use a trick that Derek Cohen taught me – it is much easier to keep the iron flat on the grit if you have a handle on the other side of the iron to grip with your hand. A magnetic base for a surface gauge was his suggestion. I use a Magjig knob. Try it – it makes it so much easier to push your iron flat across the grit.

  16. Chris F

    The above illustrations are pretty close to the way I see it as well. Of course, with a lapped blade from L-N or LV (and probably others too) you don’t have the deep scratches to start with so the whole process goes much faster.

  17. Wilbur Pan

    I’ve been studying your drawings, and I don’t get it.

    You’ll have to come over to my house. :@)

    Don’t worry, I’ll fire up the grill, and have a large quantity of grillable items available. :@)

  18. Hank Knight

    Chris,

    That’s about as concise and well illustrated a tutorial on flattening a plane iron as I have ever seen. It’s not rocket science, but it does help to know what you’re lookng for. I think your explanation hits the mark there very well.

    Hank

  19. Kevin Kuehl

    I didn’t mention David’s "ruler trick". What I’m describing is the method he shows for flattening a plane iron’s back. I think he calls them "motion 1" and "motion 2" or something like that. I like his criss-cross method because I think it’s simple to see when you’ve accomplished your goal. You can also use it on wider chisels too.

  20. Christopher Schwarz

    Kevin,

    Of course the ruler trick and other methods from David work beautifully. The principles are the same — remove the scratches at the cutting edge.

    I purposefully avoided discussion of the ruler trick because I have enough cans (barrels perhaps?) of worms open at the moment.

    Chris

  21. Kevin Kuehl

    For plane irons, I like David Charlesworth’s method for flattening the plane back. You start with something around 1000 grit, going side to side until all your scratches are side to side. Then you switch to top to bottom until all your scratches are top to bottom. Then you switch to 4000 grit and do the same. On 8000 you only go top to bottom. Oh yeah, and you flatten, flatten, flatten, flatten your stones along the way. 🙂

    Everything is explained in his "Plane Sharpening" DVD from Lie-Nielsen. He’s also got some other great tricks in this DVD. It has been a great help!

Comments are closed.