How to fix a damaged edge

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Video transcript: 

When you buy a vintage tool at a flea market or online, you can be almost certain that the cutting edge is dull. But quite often, the edge isn't not just dull. It has often seen all sorts of abuse. Sometimes yo'll see that the tool has never been properly sharpened. And sometimes, you'll see that it *has* been attempted sharpened, but in a way that has gotten the cutting geometry way off.

In almost all cases, this can be fixed. Underneath this bad edge, there's good steel and a fresh, keen edge, that's just waiting to be exposed.

So that's what this video will be about: I'll show you how I take an old, neglected tool and make it cut wood again.

This is a chisel from a flea market. It's a good quality tool, but it looks like it has never been sharpened. Perhaps you can see the rough grinding marks on the bevel side of the edge. Those are the factory milling marks. The back of the tool also has the matte sheen that shows it has never been polished. The yellow stuff ... is that glue? Perhaps the chisel ended life with its original owner as a glue scraper.

Something that surprises a lot of people is the fact that when you buy a new edge tool, it usually doesn't come sharpened from the factory. So a brand new chisel or plane will - usually - not cut very well out of the box.

I think this is one of the things that often puts people off from using hand tools, because the initial experience is so disappointing. Only expensive, premium tools come pre-sharpened. And even these tools will benefit from a honing before you put them to use.

Perhaps you can also see that the edge of this chisel is quite chipped. So it seems that the tool *has* been used, at least once. Most likely, it has been a pretty bad experience, because it was never sharp. And perhaps that's the reason this the tool has been put away and never re-sharpened.

This is actually good for me, because there's still a lot of steel, and the geometry of the edge - the 25 degree bevel that the factory made - is still intact. All I need to do is to grind away the chipping, hone a 30 degree micro bevel and polish both sides of the edge. This should give me a very keen edge that can shave off end grain without problems.

Here's how I go about it:

First, I grind off the chipping at the edge. To make sure I grind it square, I use my square and a Sharpie marker to draw a line right at the edge.

Then I grind it flat until all the chipping is gone. Only very little material needs to be removed, so I'm being very careful here.

Now I want to set the tool rest of my grinder at 25 degrees, so I can grind the bevel of the tool and establish the zero radius intersection. To get the grinding angle right, I'm making a small angle gauging block.

I use a protractor to mark the angle, and then I cut it out with a hand saw.

At the bottom of the block, I've marked the thickness of the chisel. I want the grinder wheel to make contact right in the middle of the bevel, so the chisel will be ground at 25 degrees. This looks about right.

My grinder has a coarse 60 grit wheel and a fine 100 grit wheel. I'm setting both at the same angle. And generally, I always grind my tools at 25 degrees, so I shouldn't ever need to re-adjust these tools rests. You don't need two wheels on your grinder - just one wheel of around 60 to 100 grit is fine.

Two things are important with a bench grinder. The first thing is that it should have an adjustable tool rest like the one I've just shown you. Second, it should have a good grinding wheel that runs without too much vibration.

The wheel on my grinder is made of white aluminum oxide. This is a friable wheel, which means that the surface of it can be renewed when it gets dull or clogged up with metal particles.

I use this dressing tool, which has coarse diamond particles on it, to renew the surface of the wheel. I use this whenever the surface of the wheel gets darker from steel particles embedded in it. The dust from the wheel should never get in your lungs, so I'm being careful not to breathe it in.

A freshly dressed wheel will cut much faster and much cooler. The reason you want the wheel to cut cool, is that you don't want your tool to overheat when you grind it. If the steel gets too hot, it will loose its temper, or hardness. You can tell if your tool has lost its temper if the steel suddenly turns a dark blue at the edge. If that happens, the entire blue area needs to be ground away.

So now, I'm working on establishing the 25 degree angle and the zero-radius intersection between the bevel side and the back of the blade. I'm checking every few seconds to see if I'm grinding it square. I've marked the entire bevel of the tool with a Sharpie, so I can see where I'm removing material. I'm taking care to hold the tool flat on the tool rest so the grinding angle is correct.

I'm also checking once in a while if it's getting too hot. It should never get too hot for your fingertips to touch. Sometimes, I use a cup of water to cool down the tool once in a while as I'm grinding it.

If you don't have a bench grinder, this work *can* be done with other tools, although it will probably take longer. One method would be to use a belt grinder. Another would be to use coarse sandpaper that you put on a flat surface such as a piece of glass or tile. If you search on YouTube, you should be able to find information on either of these methods.

Now, I'm done grinding. All the sharpie marks are gone, and I've ground a bit more after that to remove the flat at the edge of the tool. So I'm back at a zero radius intersection, the edge is ground square and at the correct angle. Now I need to hone and polish it, to make it sharp and strong.

I'm starting with the back of the tool. I want it to be flat and polished to a high shine. From the factory, it's rarely perfectly flat, and it's usually not polished either. Here you can see what the first few strokes on the coarse stone did. I need to keep on working until the factory grinding marks have been removed from the entire edge. This can take some time with a new tool. But it is a job you only need to do once. Once the back of your tool has been polished, it will stay that way, regardless how often you grind the bevel side.

My sharpening stones are actually not stones, but steel plates with diamond dust on them. I have one that's coarse and one that's extra-fine. The big advantage of diamond plates is that they don't get hollow as you use them. And they just need a splash of water for lubrication and to remove the metal particles that are ground off.

Waterstones or oilstones get hollow with use, so you will need to flatten them from time to time, for example with sandpaper on a piece of glass, - or with a coarse diamond plate.

Now, we're getting closer. Just a bit more work with the coarse grit.

Now I've removed the factory grinding marks at the edge. The next step is to polish it. So I'm moving on to my fine stone.

Perhaps you can see how some of the scratch marks from the coarse stones have been removed and polished to a higher shine?

I want that shine across the entire edge, so I'll need to do some more work on the fine stone.

This looks OK.

Note that this job of flattening and polishing the back only needs to be done with your chisels.

With plane blades, theres's a trick you can use, which saves quite a bit of time. It's known as "the ruler trick". It works like this: you place a thin steel ruler on your sharpening stone before you start polishing the back. This creates a slight angle, so you're only polishing the very edge of the tool. This works well for hand planes, because it only makes a minimal difference in the cutting geometry.

But for chisels, I don't recommend it. The back of a chisel should be perfectly flat, because that will allow you to make a flush cuts, using the back of the tool as a reference surface.

Now I'm ready to start working on the bevel side. I want to hone a micro bevel at 30 degrees. So first, I'm making a block of wood that's 30 degrees. Then I'm using the block to set the chisel correctly in my honing guide. So edge tools can be sharpened free hand, but I've found that I get more consistent results with less effort when I use a honing guide.

This is a so-called "Eclipse" style honing guide, which has a roller under it and two jaws on the sides to grip the tool.

In the case of this particular honing guide, the offset for a 30 degree angle is around 29 mm.

I've made a holder for my sharpening stones that have stops built-in that make it easy to consistently set the tool at the correct angle in the honing guide. The stop at the left is 25 degrees and the one at the right is 35 degrees. But I actually only use the one in the middle, which is 30 degrees.

So now I start working on the coarse stone. I'm checking to see, if I've established a micro bevel all the way across the edge, and I'm feeling for a hook burr with my finger.

Once I can feel a burr all the way across the edge, I'm moving on to my fine stone. Now I want to polish the edge until I've removed the scratch marks from my coarse stone. How much is that? Well, it depends on which stone you're using - how fine it is and how fast it cuts. With my stone, it's probably around 20 or 30 strokes.

Here, you can see the micro bevel. It's almost all the way across the edge. Perhaps you can also see the burr showing at the left side of the edge.

I *should* probably have done a bit more work on the coarse stone to get it all the way. But it's so close to being there that I think I can just do a few more strokes on the fine stone to get a micro bevel all the way.

Now, it should be OK.

The final step now is to polish the edge, so it gets the last bit of strength and sharpness. For this, I'm using my strop. The strop is a flat piece of wood with some leather glued onto it that has been charged with a fine aluminum oxide honing compound.

First, I'm stropping the back of the tool. Note, that I'm only pulling the tool - if I move it back and forth as I did on the stone, it will dig into the leather. I'm making sure to hold the chisel flat on the strop so I won't round over the edge. To get a good polish to the back of the tool, I'm stropping it quite a lot. This will remove the scratch marks from the fine sharpening stone.

Here, you can see the almost mirror-like polish.

And here, you can see the wire burr that fell off during the stropping process.

Now I want to strop the bevel side of the tool. I do this freehand. First, I feel for the 25 degree primary bevel by tilting the tool a bit up and down. Once I feel it, i tilt the tool upwards a bit to hit the 30 degree micro bevel. I'm trying to be reasonably accurate, but because the leather is soft, it still works fine if I am a few degrees off.

Again, I'm only pulling the tool, so I won't dig into the leather.

I'm doing around 50 strokes on the bevel side. In my experience, more stropping is better than less, especially if you're about to do a job where you need a really keen edge.

Then I'm switching back and forth a few times between the back and the bevel side. In that way, I'm making sure all of the burr has been removed.

Here you see the two polished surfaces that - in combination - make up the zero radius intersection we're looking for to make up the cutting edge.

Now, let's try out the tool to see if it's really sharp. There are a few different ways to do this, but I've found that the best way for me is to simply cut some wood.

If your tool cuts end grain wood cleanly and reasonably effortlessly, then It's sharp. This is a board of pine.

Now I've restored and sharpened the tool. It did take a while. But next time I need to sharpen it, it should only take a fraction of the time, because I've already established the edge geometry and polished the back of the tool.