Monthly Archives: July 2009

Sharpening Class Part II – Am I There Yet?


“Are we there yet?”

“How much longer?  I’m bored!”

Now the quiz:

These questions are:

a.    Things my brothers, sister and I used to say on the way from our home to our grandparents’ farm, a drive of some 40 miles.
b.    Questions our own kids ask during our camping trips.
c.    Comments from my sharpening students as they flatten the backs of chisels and plane irons.
d.    All of the above.

If you answered “d”, you win.  Unfortunately, the prize isn’t a swell gadget to flatten the backs of tools any faster.

Getting Flat

Remember the first lesson.  We’re after two flat polished planes. And remember that the road we take to get there is one of our own choosing.  I’ll make a few suggestions, but you should experiment to see what works best in your own particular situation, in your own shops.

Remember too that everything starts with our shop’s flat reference surface.   Whether you choose a piece of glass, a granite test plate like I use, or another surface, everything starts with the reference.  Here’s what to do and how to go about it.

First off, we need an abrasive.  Silicon carbide (SC) sandpaper (known as wet-or-dry paper, usually black) is a frequent choice.  So are Japanese waterstones.  There are many others – more on this at the end of the post.  In my shop, I use both of these.  My synthetic Japanese waterstones are in grits of 800, 1200, 4000, 8000 and 10,000.  I try to keep an inventory of SC paper in 220, 320, 400, 600, 800, 1000, 1200, 1500 and 2000 on hand.

For starters, let’s choose SC paper as an illustration.  You can use full or partial sheets as you choose.  Place a sheet of abrasive (let’s start with 220, assuming that we do not have a ton of steel to remove) on your reference surface.  If you hold the abrasive with your off-hand, and manipulate the tool with the other you’re making extra work for yourself.  Instead, use an adhesive to hold the paper to your reference surface.  A word of caution here, though.  If the adhesive you use isn’t flat, you’re beginning to introduce error.  Some folks like 3M No. 77 spray adhesive.  I don’t use it because of the flatness issues: I don’t know that I can spray a perfectly even coat, so when I need to fix the paper to a surface I use 3M No. 9589 tape.  If you delve into the specs of this tape far enough you’ll understand why.  For now let’s just say that 3M measures the thickness of the sticky adhesive and the plastic base to three digits.  It’s fairly precise stuff.  There’s another good reason for this tape, discussed below.

In any event, we’re now ready to begin.  The abrasive is either fixed or held flat on the reference surface.

Time to Flatten

Here we go.  Grasp the chisel or the plane iron firmly and begin to move it across the surface of the paper.  Move the steel consistently back and forth, without rotating the tool in relation to the paper.  What we’re after is a series of consistent scratches in the steel that look like straight lines.  Not swirls or curves.  Straight lines.  You’ll appreciate this detail in a little while.  We only need to flatten about an inch or a bit more of the back of the tool, so don’t waste time and effort doing the entire back.  Absolutely not necessary.

This is where the drudgery comes in.  This part of the process takes some time.  Play some music, listen to talk radio, talk to the dog…but remain focused on the task at hand.  Most important here is to keep that tool dead flat on the abrasive.  Hand position is important: keep your hands away from the handle of the chisel or the rounded end of the plane iron.  Concentrate your effort and your attention over the portion of the tool you’re working.  Don’t rock the tool off the edge of the glass or granite or you will make more work for yourself.  Every so often, if you are using the paper dry, brush away the small metal shavings that are beginning to accumulate on the surface.  If you’re using the paper wet, squirt on a little more water every so often.  Dry paper cuts faster and wears out faster.  Wet paper – just the opposite.  Since I like to move through this part of the journey fairly quickly, I most often use the paper dry.  As you work this first tool, this frightening thought will pass through your mind:  every cutting tool in your arsenal deserves the same care and preparation.  The good news is that tools only get flattened once.  You’ll spend the rest of your days honing, but honing goes a lot faster than flattening.

The way I like to look at flattening is a gradual and systematic process of erasing scratches.  This first pass with the coarse paper erases the scratches left by the manufacturer, or, if it’s a used tool, by years of rattling around in someone’s tool chest.  It also gives me a base, or a ground, of scratches that are of a consistent size and depth.  Finally, it gets you down the road – when you’re done with the first grit, your tool should be as flat as your reference surface.

Think of yourself as an artist (which you are, of course) preparing a canvas with a background color wash.  I find that this is the place where some modest magnification helps.  If you can see scratches that run in a direction other than the ones you’re leaving behind with the abrasive, you’re not done yet. (See the quiz at the beginning of this post.)  When there is a consistent scratch pattern that runs uninterrupted from side to side, and runs completely off the cutting edge of the tool, you’re done and the back is flat.  No left-over marks from the grinding process.  No pitting from rust.  Clean, shiny metal, consistently scratched by your abrasive.  That’s when you’re done.  Use a jeweler’s loupe, or a small magnifier, about 10-15 power.  You WANT to find those errant scratches and erase them.  This step is the single most important in the flattening process.

A word here about tool quality.  Manufacturers don’t do this work for you simply because it costs too much.  Having said that, you have every right to expect good quality tools like Lie-Nielsen chisels and plane irons, and Hock irons, to be flat.  They won’t be polished but they should be flat.  In the unlikely event that you run across one that isn’t flat, you should call the place you bought it and arrange an exchange.  Less-expensive tools may not be machined to the same level of finish, or to the same precision, and you’ll have correspondingly more work ahead of you.   If your time is valuable to you, then it is worth spending the extra money to shorten the flattening process.

Used tools are a crap shoot.  If you can inspect the tool before purchase, like you would at a flea market or garage sale, bring along a little 6″ straight edge and a magnifier.  Look for pitting with the magnifier, and check flatness with the straightedge.  Once you’ve tuned up a few tools that are badly out of flat you’ll appreciate how much work it can be, and will suddenly become more discriminating in your used tool purchases.  Don’t worry too much about the condition of the bevel, because you’re going to shape that to suit your use.  Of course, if the steel is badly rusted or pitted, I would think four times about buying.  Not just twice; four times.  Handles can generally be replaced, but that process will add work to the process of turning your treasure into a useful bench tool.

If you shop on eBay, Craig’s List or other online sources, I wouldn’t buy a tool from a supplier or seller  who wouldn’t take it back in the event it is badly out of shape.  Be sure to ask the seller about the return policy first, before you bid or purchase.  Caveat emptor.

Things to Watch For

If you are using a silicon carbide paper to flatten your tools (and holding this paper down by hand) you may find some chisels and plane irons resist flattening all the way out to the tip of the bevel.  It will seem as if about 1/32″ – 1/64″ is rounded away from the back of the chisel, and the scratches just don’t hit that portion of the steel.  While I don’t know this for certain, I suspect that this may the result of the paper rising up slightly, just in front of the tool’s leading edge as you move it back and forth.  I don’t think it is an artifact left from the manufacturing process.  The solution to this issue is to adhere the paper to your reference surface with the tape mentioned earlier in this post.

If you find the back edges of the chisel are sharp – the edges running from the long point of the bevel up to the handle – you can relieve them with a light stroke or two with a fine file.  You won’t want them sharp, because your hands spend a lot of time in that area while honing.  Just don’t file all the way down to the bevel.

Choosing a System For Your Shop

Silicon carbide paper works well, no doubt about it.  It also wears out quickly.  Because I am not entirely conscientious about restocking paper, more than once I’ve found myself out of a particular grit when I need it.   Not all stores carry the finest-grit papers; your best bet will be auto body repair suppliers, or the Internet.  These inconveniences, and the recurring cost of constantly resupplying your inventory are drawbacks to using SC paper as your only flattening system.  I’ll write more on this in the next post, which focuses on obtaining a polish on the steel.

Earlier in this post I mentioned Japanese waterstones.  These are a fine alternative to SC paper, and I use them exclusively for honing and occasionally for flattening.  The process of use is the same, but you’ll have a bit of prep work on the stones before you flatten or hone.  And once again, it all gets back to your shop reference surface.  This time, though, you will flatten the stone on the reference surface before use.

Japanese waterstones are renowned for their ability to cut rapidly and leave a fine edge behind.  They do this because the abrasive grit in the stone is bound with a clay-like binder that wears away fairly quickly, constantly exposing new abrasive particles.  One drawback this poses is the tendency of waterstones to dish out in the areas most heavily used.  And that dishing is corrected by flattening on the reference surface.

Take your 220 grit paper, hold it flat on the reference, and move the stone back and forth.  In this case, use the paper wet.  After a few strokes, look at the face of the stone.  If you’ve used this stone in the past, you’ll most likely see an area or two of dark grey or black running the length of the stone, and these areas will be surrounded by nice clean areas, the color of the stone.  The dark streaks are the hollows, and you’re seeing the swarf, or byproduct of earlier sharpening sessions.  Your objective here is to remove the dark streaks and see only a pristine, new surface of the stone.  Once you have arrived at this condition, your stone is as flat as your reference surface.  Do both faces while you’re at it.  And as a final touch, rub each edge on the abrasive (2 long edges and 2 short edges on each face) to create a chamfer.  Do the same with all 8 corners.  These last few steps will stop you from chipping an edge or a corner, which can happen fairly easily with these stones.

Once your stone is flat you can get to work on the tools.  You will need to periodically flatten the stones, but that shouldn’t take a lot of time.  As you flatten the plane iron or chisel, work it over the entire surface of both faces of the stone.  That way you will maximize the use of each flat stone surface and minimize the amount of time you spend reconditioning your stones.  Finally, when you’re done sharpening for the day, touch up your stones while you still have the mess in front of you.  That way everything will be ready for next time you get a wild hair and buy another cutting tool.

Once you have a nice, consistent pattern of scratches over an inch or so of the back of the tool, you’re done with this first step.  You should now have a tool with one plane that is as flat as your shop’s reference surface.  It isn’t polished yet; we’ll cover that in the next post.   Depending on the condition of the tool when you started, this step might have taken an hour or more from start to finish.  I can’t emphasize enough how important it is to take your time, and be patient.  The results really are worth it.  And don’t despair; if you have truly done a good job with this first grit, and your scratches are nice and consistent, the subsequent steps go a lot faster.

We’re not there yet…but we’re getting close.

Next:  Sharpening Class, Part III – Getting your Shine On

_______

Jeff Zens owns and operates Custom Built Furniture in Salem, Oregon. He is a frequent woodworking instructor and writer.

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Sharpening Class, Part I


“When we build, let us think that we build for ever.”

English artist and writer John Ruskin wrote that in The Seven Lamps of Architecture. It’s a quotation that inspires us to do our best work, because that work will reflect on us for a long time.

Sometimes we take that quotation and apply it, mistakenly, to our sharpening practices. We either sharpen too infrequently, or not at all. We think that if we sharpen once, we sharpen forever. We fool ourselves. We might operate with the belief that when we purchase a tool it comes to us sharp and ready to use. I think for some tools the truth is a long way from our belief; for  other tools it’s a bit closer. But the sad fact is no matter where we purchase our edge tools, there is always some work to be done.

In my sharpening classes, I’ve bumped up against all kinds of reasons woodworkers use dull tools. Of course the one most often expressed is lack of knowledge. People just don’t know how. Well, no one is born knowing how to sharpen, any more than they understand at birth how to cut a dovetail. That’s why they come to class. Another reason – surprisingly – is that folks are afraid to mess up their tools. Better to use them dull. Here are a few secrets about your tools. First, they are yours, so you can use them as you see fit. You can grind them, change bevel angles, and so on. You can also choose to use them as they are (dull), but why? Sharpening can be practiced and mastered. Second, there aren’t too many sharpening mistakes that cannot be fixed. Probably the worst thing that can happen is that a tool gets blued – you draw out the temper – by overheating when grinding. Even that one can be fixed, but more on that in a subsequent post.

Understanding how to get sharp tools is essentially a two-stage process, with a few sub-steps thrown in for good measure.

The Theory

Step one involves a deep understanding of what makes up a sharp edge. It’s the most important part of this whole deal. Skipping this lesson during sharpening class will cause a person to skip vital steps while sharpening a tool. It’s the part of sharpening that seems to trip up most people who have trouble obtaining a keen edge. The key is to understand this definition of theoretical sharpness: a sharp edge is the intersection of two flat, polished planes at a point approaching zero thickness. Translating that theory into practice becomes a matter of personal choice based on individual experience, but this is the end we’re trying to achieve. There are a lot of roads we can follow to arrive at this destination. The one you choose should be the one that works best for you – not the one that involves spending the most money.

Flattening the Back

Logically, obtaining two flat, polished planes involves working both surfaces of a cutting tool: both the front and the back. For this discussion, the front of the tool will be the beveled face, and the back is the opposite surface. Most folks who are new to sharpening either fail to work the back of the tool at all, or they don’t do it enough. We’re going to start with “flat”. Understanding “polished” will come later. Here’s why flat is important.

Think about the role the back of a chisel plays in your work. It is the part of the tool that registers against the workpiece, and “aims” that sharpened cutting edge for you. If you’re familiar with the concept of a reference surface, the back of the chisel plays that role.  When you pare the face of a small tenon, it’s the back of the tool that rides along the surface of the wood as the edge removes high spots. So if your chisel is to do what you want it to, the sharpness of the bevel must only shave off the high spots and leave the low spots alone. The only way you can reliably cause that to happen is with the back of the tool held dead flat against the workpiece.

Now visualize the back of that chisel. Can it be held dead flat if it isn’t dead flat itself? What if there is a slight swelling of the steel – say a few thousandths of an inch – just behind the cutting edge? If that swelling is present, you’d have to raise up the handle a bit to engage the sharp edge in the workpiece. That swelling would act like a fulcrum – a pivot point. Drop the handle down, and the edge doesn’t engage the high spots you’re trying to pare away. Raise the handle up too much and you’re taking away too much wood.

Not significant, you say? Well, think back to Ruskin. We’re building forever. So when we make that mortise and tenon joint, the fit has to be just right. Some call it a piston fit. Not loose, not sloppy. Just right. Eventually all glues can fail. When that happens, will your joints still have structural integrity, or will they simply fall apart? So yes, it matters.

There are two more equally important reason we strive for absolute flatness for the tool’s backs and bevels. First, it’s repeatable, and repeatable makes for consistency, and that is what we want from our tools.  We want them to work the same way every time we pick them up.  If they don’t, we need to learn how to use them over and over – and who has time for that?  If, every time you hone a plane iron you put a slightly different shape on it, it’s going to work slightly differently.  The surface it leaves behind won’t be the same as last time.  If your stones are cupped, or the edges are lower than the center, your steel will take that shape.  But because the stones wear, the shape will change from one honing session to the next.  Flatness is the one constant we can depend on.  The second reason is just as important, but a little obscure.  The surface of the back of the chisel or plane iron forms one-half of the cutting edge.  Consider that for a moment, and then ask yourself why you would ignore the back if you really wanted a sharp edge!

Start with a Flat Reference Surface

How do we get this flatness? We need a flat surface with which to start. If the work done by our flattened chisel back is the desired destination, then our shop’s flat “reference surface” is the place we start this trek. In my shop, the reference surface is a granite test plate. I know its flatness. It’s certified flat to 0.001″ diagonally across its 12″ x 18″ face. A lot of people use a piece of float glass, since that’s the “flattest glass available.” Problem is, I don’t know what that means. I can’t find a standard for glass flatness, and I wouldn’t know if my piece of glass met that standard. Don’t know if there are waves, dips, depressions, or any other deviation from flat. So rather than mess with the unknown, I started with the test plate. They’re not terribly expensive if you purchase a “second”, known as tool-room grade. Mine has a small chip from the edge of the face. Perhaps one square inch of the top is blemished, and this doesn’t affect the flatness one bit. The big drawback? These test plates are very heavy, especially in the larger sizes. So they’re a load to lug around, and the shipping costs can be a bit steep. Because this is where it all begins, it’s worth it to spend a little money.  Is this obsessive?  Perhaps.  Would glass work just as well?  Maybe;  I don’t know.   I know this, though: I’m entirely capable of introducing plenty of variations to precise flatness with my own imperfect technique.  I don’t need additional help, so I try to eliminate as many sources of error as I can.  And I know one more thing: it works.

Next:  Sharpening Class Part II – Am I There Yet?

_______

Jeff Zens owns and operates Custom Built Furniture in Salem, Oregon.  He is a frequent woodworking instructor and writer.

Categories: Sharpening, Woodworking | Tags: , , , | Leave a comment

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