If you do any sort of woodworking for your boat, keeping a sharp edge on your tools is very important. Sharp tools produce better work, cut with less effort and can be safer to use because you do not have to force them, so there is less pressure behind the cutting edge.
Sharpening plane and chisel blades is not that difficult, but there always has been some mystique surrounding the process. In an effort to dispel any sort of myths once and for all, here is my method for producing very sharp edges on chisels and plane blades.
You don’t need a lot of equipment, but what you use must be in good order, and I’ll explain this in more detail as we go through the process. I also must explain that there are many ways to sharpen tools, but after 40 years I have found a method that works very well for me. Other people will have different opinions and methods, and that’s fine, but as with many things, you need to practice and perfect one method before trying something new. I used to work for a national woodworking magazine, and each year we would have a four-day show, during which I would demonstrate tool sharpening. One of the first questions I would be asked was, “Which grinder do you use?” — never “What’s the best way to get a very sharp edge on my tools?”
With a few exceptions, chisels and plane blades have two bevels — often called a primary and secondary bevel. Other names are the grinding angle and sharpening angle. Irrespective of what you call them, these are 25 and 30 degrees, respectively. If you are new to sharpening, it may be tempting to have a go initially with a narrower blade, but this can be a mistake, and I would caution you against it until you become proficient.
It is easier to burn the smaller-width blades on the grinder, as there is less of a heat sink to direct the heat away from the ground edge; the blade is more likely to rock, giving an out-of-square blade; and, perhaps most important, the water stones are soft, and it is easy to gouge them and nick the surface. The pictures show a well-chewed-up inch-and-a-half chisel, but an inch-wide chisel is a good compromise.
When I started off in my woodworking career, just about everybody used oil stones, often double-sided manufactured carborundum stones. These work well enough, but some years later I tried water stones and have never looked back. They cut much faster than oil stones, and as their name suggests, they use water as a cutting agent and lubricant.
They are natural stones that come in a variety of grit sizes, and although I have a large selection, I tend to fall back on two grits: 800 for the fast removal of metal and restoration of the primary or grinding angle, and 6,000 grit for final sharpening. With these two I can do just about all of my sharpening.
Although I am using the electric grinder in the photographs, I normally only revert to the grinder if the edge is severely damaged. For day-to-day sharpening. I initially use the 800 grit on the primary bevel and put the final edge on the tool with the 6,000 grit stone. It all sounds like a lot of work, but in reality, sharpening is fast and effective, providing you keep your planes and chisels in good order. If you have the luxury of a workshop or a space you can call your own, a permanently set-up space for sharpening is ideal; touch-ups happen without interruption, and the inevitable mess can be kept away from the woodworking area.
A couple of points about the care and feeding of water stones would not be amiss here. Water stones are more fragile than oil stones, so if you drop them they will likely break. Also, keep them in water. This does two things: It keeps them instantly ready for use, and any dirt floating around the shop will settle on top of the water, not on the stone.
Change the water often. I like to add a little dishwashing detergent to the water; it breaks the surface tension, and I think it adds a little speed to the cut. Lastly, if the workshop is cold, don’t let the water freeze, or the stones will shatter. Add non-toxic antifreeze during the winter months if this is a concern.
One of the issues with oil stones was that if they started to wear unevenly, it was almost impossible to true them up. Water stones, on the other hand, are soft and can be trued by rubbing two stones face to face or on a sheet of plate glass to which is taped some wet or dry abrasive paper — well lubricated with water — taking minutes for what used to take hours.
The chisel I am using here is in rough shape and has been used for everything from opening paint cans to scraping barnacles off a propeller. Normally I don’t recommend this treatment for any chisel. They should be kept for the purpose for which they are designed: cutting wood.
The primary bevel
If the edge is chipped or rounded, restoring the primary bevel is the first step. You can do this by hand, but the best way is to use a high-speed grinder if things are especially bad. One word of caution here: More tools have been ruined on high-speed grinders than by almost any other machine. A grinder will remove a lot of metal in a hurry, and it is very easy to burn the steel and remove the temper. Caution is the watchword here.
I use an 8-inch-diameter wheel, which is far better than the 6-inch models. First, the wheel is obviously a larger diameter, so the hollow grind will be less pronounced. (Hollow grind is the grinding wheel’s tendency to make the bevel concave, and this is more pronounced with a smaller-diameter wheel.) Second, there is less chance of burning the tool edge. As an added benefit, the wheels are wider and produce a more consistent edge across the blade.
I think it fair to say that the tool rests that come with grinders are for the most part useless and certainly are no good for grinding chisels and plane irons. What is needed is a robust, easily adjustable rest that holds the tool at the correct angle. I have used the superb O’Donnell jig, which, sadly, is no longer manufactured.
Buy or make a rest that will allow the tool to address the wheel at 25 degrees — the angle required for the primary bevel — and this will do much to start you off on the right foot. With the chisel on the tool rest, gently feed it forward until it contacts the wheel. Slide the blade from side to side, making sure to keep it perpendicular to the wheel (Photo 1). You will see that I have a slot in the tool rest and a small T-square to hold the blade at right angles to the face of the wheel, which does much to ensure success. If you keep the blade moving by traversing from side to side across the wheel and use a light touch, you will not overheat the edge and blue the steel.
Frequently remove the chisel from the tool rest to check progress; do not be in too much of a hurry. Keep grinding until you start to see sparks just coming over the top of the blade edge — a sure sign that you have ground down to a feather edge. Remove the tool and turn off the grinder.
Place the blade in a sharpening jig and finger-tighten the knurled knob. Place a steel straightedge or ruler across the wheel on the sharpening jig and the blade edge. Hold the blade up to the light and adjust the jig up or down until the straightedge rests on the jig wheel and the front and back edges of the hollow grind (Photo 2). Use a screwdriver and fully tighten the jig so that the blade is firmly gripped (Photo 3). Then recheck with the straightedge to ensure nothing has moved.
Remove the 800 grit stone from the water and place it on a non-slip pad (Photo 4). With the blade and jig wheel in contact with the stone, move it back and forth. Keep moderate pressure on the tool edge with your forefingers (Photo 5). Keep the stone wet by dripping more water on it as required. Occasionally lift up and inspect the chisel to check the progress.
After a few minutes, you should notice the marks left by the grinder starting to disappear and a flat bevel forming (Photo 6).
Keep going until all grinding marks are gone and you end up with a perfectly flat bevel (Photo 7). Use the full width and length of the stone to prevent wearing a groove. If you have done this correctly, the blade bevel should be dull and flat. You should keep going until you can feel a very slight burr at the tip of the blade on the flat back face.
The next step is optional, but it does produce the keenest edge. Without moving the sharpening jig, replace the 800 grit stone with the fine 6,000 grit. Then return the chisel to the stone and continue as before, but this time you’re just removing the marks left by the 800 grit stone. A highly polished surface will quickly result.
The secondary bevel
Slacken off the clamping knob on the sharpening jig and slide it toward the tip about a half-inch, which will increase the bevel to 30 degrees. Then retighten the jig and firmly but lightly rub the blade edge up and down the fine stone. This should only take eight to 10 light rubs on the stone because the prepared edge is so fine and true.
The edge should be no wider than 1 mm. There is no purpose in continuing to rub longer than this. All you will be doing is wearing away more metal, and the blade will not be any sharper. Carefully remove the chisel from the sharpening jig and turn the chisel over, and with it perfectly flat on the stone rub it back and forth a couple of times to remove any slight burr (Photo 8). The blade will now be perfectly sharp, and in fact — although I do not recommend it — you should be able to shave with it.
Trueing the Wheel
A grinding wheel that is ridged or rounded over is very poor for gringind planes and chisels. The best wheels are square, clean and true. Wheels can be dressed with either a star dresser or a diamond. I prefer the later, as it is easier to control and does a better job, in my opinion. The daimond type can be rolled from side to side across the face of the wheel to true it up. Any time you use a grinder, wear adequate eye protection. Also, wear a dust mask when trueing up the wheel.
May 2013 issue