If you are into woodworking, you probably have accumulated a bunch of dull chisels over the years. You get frustrated every time you need to use one since they are not sharp enough. Maybe, you tried to sharpen them a couple of times, with bad results. It’s common to burn them if you go too hard on a bench grinder. So, I guess it’s time to learn how to properly sharpen a chisel.
If you are wondering if you can sharpen your chisels on your bench grinder, the answer depends on the work you will do with that chisel. For fine woodworking, you need a bench grinder to get the bevel of the chisel back on track; then, you need to smooth its surface on honing stone or fine sandpaper. For a coarse sharpening, proper use of the grinder (and a proper wheel) will be enough.
If your tool is not in bad shape, you can skip the bench grinder passage and go right to the honing phase.
If we are talking about a chisel that you will use for fine woodworking, then you should consider grinding as a shaping operation; then you need to do the refinishing job either on sandpaper or honing stone. You can get away with just a bench grinder when you want to sharpen an ax or some other gardening tools. For a chisel that you are going to use in fine woodworking, that is not enough.
Now, let’s get to the process. First, we are going to talk about sharpening chisels that you will use on heavy-duty work (for example, shaping a rock for your garden project, cutting a metal rope, etc.). Then we will talk about fine woodworking. After that, we will discuss how you can sharpen whatever other tools you have (for example gardening tools).
First, let’s address what kind of wheel you need to do the job.
What Grinding Wheel do I Need to Sharpen My Tool?
For the purposes of this article, there are only two types of wheel you need to consider: gray and white. You will find a lot of different ones on the market, and it can be quite confusing for a beginner, so we will stick to the basics.
A grinding wheel is made of thousands of abrasive grains that stick together thanks to a bonding material. There are a lot of abrasive types, the most common one is aluminum oxide. The color of the wheel (and its price) is decided by the oxide’s purity. Now let’s talk about gray and white wheel.
- Gray wheel: this is the most common type. These are general-purpose wheels that can grind most steels. This type of wheel is enough if you don’t need to get a razor-sharp result. It’s important to get the grain size right: a grain too fine is overkill in this case. A 60-80 grit wheel is more than enough.
- White wheel: This kind of wheel is made of nearly pure aluminum oxide ( therefore the white color). You need one of these if you want to get a razor-sharp chisel. They are suited for heat-sensitive steel, which is a common choice in chisels.
What is the Bench Grinder’s Proper Speed for Sharpening Tools
A lot of people worry about bench grinder’s speed. Usually, you have two kinds of bench grinders: slow and fast ones. Slower ones rotate at about 1800-2000 rpm, and they are ideal for this kind of job. Faster ones rotate at about 3500 rpm. If you have a variable speed bench grinder, set it to the lower end. If you have a fast bench grinder, don’t worry, you can still use it. Just work with a light touch, to avoid grinding too much material at once. Also, check frequently for overheating (we are gonna talk about it in the following paragraph.)
How to Sharpen a Chisel on a Bench Grinder (for General Purposes)
If you don’t need to get your chisel sharp as a razor, then the process is easy, but it will require some practice to master it. In this case, you are going to need a common gray wheel to put on your bench grinder.
Here are the steps to follow to get the job done:
- If your wheel is new, you can skip this step. But if your wheel has been used quite some time, you should consider cleaning and dressing your wheel with a dressing tool. There are a lot of different ways to do this. The most common way is by using a dressing stick. Set the grinder’s tool rest to a 90 degrees angle, and move the stick back and forth against the wheel’s surface. Move the stick slowly to remove less metal and get a smoother surface on the wheel. This way, you will also get a finer surface on your chisel.
- Now you need to sharpen your chisel. To do this, you need to get the chisel’s bevel back in track. A 20 degrees angle’s bevel is a safe choice. To get the proper angle, set the grinder’s tool rest to the proper angle. To make your life easier, draw your angle on a piece of cardboard, cut it with scissors, and use it as a guide to check your rest’s angle.
- After setting the angle, you can start sharpening until you get the bevel right. During this step, you need to check the chisel frequently for overheating. You want to avoid overheating your tool. If the temperature goes up too much, you will get a blue edge on your tool, and you will lose the steel’s temper. As a result, your chisel will get weaker.
What can I do to Avoid Overheating?
To avoid overheating, you can do two things:
- Check the tool near the cutting edge frequently with your fingertips. If you can touch it without problems all the time, that means that the temperature is ok, and you won’t have to worry about losing the steel’s temper.
- If you don’t want to risk burning your fingertips, you can use a cup of water instead. Dip the tip of the chisel frequently in it to keep it cool. If the water doesn’t sizzle, you are good to go.
That’s it if you wanna do a coarse job. For fine woodworking, check the following paragraph.
How to Sharpen a Chisel on a Bench Grinder (for Fine Woodworking)
In this case, you need a white wheel. It is much easier to avoid overheating your tool’s edge (watch out, though: if you press too hard, you will get a burnt edge even with a white wheel). If you have a variable speed grinder, you want to set it to the lower end. If you have a fast one, remember what we said earlier. Feed the chisel slowly to the wheel.
- If your chisel is dull, you want to get the bevel in shape first. You can follow the guidelines I gave you in the paragraph above. That’s the only thing you are going to do on a bench grinder. After that, you will need some sandpaper and honing stone.
- For the next step, you need some sandpaper sheets. Adhesive back sandpaper or common sandpaper glued down to a flat surface (for example, a piece of plywood) will do the trick for you. You need 3/4 different types of sandpaper, from coarse to fine. For example, 80-120-220 grit sandpaper sheets.
- First thing, you need to work the back of the chisel. You want to make it flat so that when you work on the front, you will get a sharp edge. Start with the coarse sandpaper, move the chisel back and forth until all the mill marks are removed, and then move onto the finer ones till you get a flat back.
- After that, we need to work on the front of the tool. To get the angle right, you need a honing guide. You can get one at your local store for a few bucks. With a guide, it will be much easier to sharpen the bevel at the right angle.
- Do the same thing as you did for the back of the chisel: start from coarse sandpaper and work your way through the finer one. Move the chisel back and forth. You will get a razor-sharp edge in no time.
How to Sharpen Other Tools on a Bench Grinder
Maybe you want to sharpen other things than your chisel on your bench grinder, a pair of pruning shears for example. In this case, you want to refresh the edges. A finer wheel may do the job for you. To get the proper angle on the grinding wheel, you need to experiment with the tool to get it right. You want to feed it to the wheel slowly, to avoid removing too much material in a certain spot.
After doing this, you should consider using a honing stone or some sandpaper if you need to sharpen it even more. An easy way to check if you sharpened it enough is by trying to do the job the tool is supposed to. For example, try to cut some branches with your pruning shears: if the cut is clean, and the branch isn’t pinched, then you are good to go.
We went through some guidelines to sharpen your chisel (and your other tools) with a bench grinder. There are a lot of ways to do the job. It depends a lot on your experience and the tools you decide to use.
To get it right, always remember to use a light touch (go back and forth slowly, to avoid grinding too much in one passage) and check frequently for overheating (I gave you two ways to do it).
The best way to learn the process is by experimenting: get some old tools, some scrap steel, and try getting a sharp edge on them. By doing this, you will avoid ruining your good tools.
The most important thing while doing this kind of job is to always put your safety first. Always wear safety glasses when using a bench grinder, since the grinding process produces a lot of chips of red-hot metal that can cause damage to your eyes.