What You Will Learn
Before You Start
Sharpening angles are one of the many things within this topic that can spark debate. However the majority of people will agree that a 25 degree primary bevel and a 30 degree secondary bevel is the best place to get started. Therefore we will be using this geometry throughout this lesson. Don't worry if those numbers or words don't make any sense at the moment. We will cover them later in the lesson.
Using a Honing Guide vs Freehand.
I would strongly recommend using a honing guide as a beginner as it increases your likelihood of producing a sharp, consistent and clean edge. They can also be relatively cheap and take no longer than 20 seconds to setup.
Sharpening freehand is slightly quicker as there is less setup involved, however you will likely face a steep learning curve while developing your muscle memory. You may also find that you spend longer trying to grind out previous mistakes caused by freehand sharpening, than you would have if you just used a honing guide straight away.
It’s completely up to you, but please take advice from experienced woodworkers with a pinch of salt. While they are able to produce a sharp edge using freehand techniques, be aware they have been practicing and developing that method for many more years than you have.
Side note: If anyone tells you that using a honing guide is ‘cheating' and you are a not a ‘real woodworker' if you cannot sharpen freehand. Walk away. They are likely too self indulgent to be wasting your time listening to.
Choosing a sharpening stone and/or grit to use
Fundamentally, the choice of stone doesn’t matter too much. Some cut quickly, some cut slower, some create a mess, some are relatively clean. The main thing to ensure is that the abrasive surface is flat. If not, your chisel will not decent perpendicular to the piece you are working on, which is a huge problem.
Grades of abrasives for sharpening can be loosely categorised into 3 types. These ranges may vary depending on who your ask and to be quite honest, it doesn’t matter too much. This is simply a rough guideline.
|Approximate Range||240 grit – 600 grit||800 grit to 4000 grit||5000 grit +|
|Use||Quickly produces the 25 primary bevel.||Produces the 30 degree secondary bevel||Polishes the 30 degree secondary bevel|
Which grits do I need?
If you want to do all your sharpening with just one grit, you can! It’s perfectly possible to re-grind a chisel using a fine 5000 grit abrasive as opposed to a coarse 240 grit abrasive. Why wouldn’t you do this? Because its going to take ages and may wear out your sharpening stone, let alone thoroughly increase your heartrate both through exercise and frustration.
As another example, you could grind a chisel to 25 degrees using a 240 grit stone then jump to polishing on a 5000 grit stone. However it may take ages to remove the scratch marks left by the 240 grit on such a fine abrasive. In this situation, it would most likely be quicker to use a honing grade in between grinding and polishing.
In order to efficiently produce an extremely sharp edge, you will need one grit within each of these ranges.
Step 1: Grinding
In this step, you are aiming to produce a 25 degree bevel. This may take a long time depending on the state of your chisels, the size, and the hardness of the steel itself. You have two ways to do this:
By Hand: Grinding on a stone by hand takes more elbow grease and generally takes longer.
By Machine: Grinding using powered equipment can be more expensive but is generally faster.
Whatever method you use, there are a few things that need to be reiterated:
How accurate does the chisel angle need to be?
Don’t stress if the angle ends up being 23 degrees or even 27 degrees instead of 25 degrees. The chisel will still work just fine. What matters is that you are able to exactly reproduce that angle next time you sharpen which is where honing guides come into their own.
Put it this way, If you are continuously changing between 23 degrees to 26 to 22, to 27, you're not only going to be spending way too much time sharpening, but you're also grinding away unnecessary amounts of metal that you have paid for. This is a common problem beginners have when attempting to freehand sharpen.
Make sure you don't overheat the steel
This is especially easy to do on high speed grinders. Doing so will soften the steel and ruin its edge retention properties. If using a water cooled grinder such a Tormek, you won't have to worry about this. When it comes to using sharpening stones, be sure to use a lubricant when sharpening (Water or Oil depending on the abrasive) in order to prevent overheating.
If you absolutely have to use a High Speed Grinder, make sure you do light, short touches on the wheel and cool the chisel in water regularly. Do not let the steel go blue.
Ensure defects have been removed
We regrind blades in order to get them back to their original condition as they were purchased. So ensure all chips, dents and rounded edges have been ground off the cutting edge before moving to honing. Failing to remove these now will mean you will have to remove them with a finer grit later in the sharpening process, which is rather counter productive.
Do you actually need to re-grind?
If you’re chisel is in a relatively good condition and just needs a quick touch up in order to re-sharpen the edge, don’t go through the effort of re-grinding the whole thing. Just skip straight to honing. As a rule of thumb, I usually re-grind the blade to 25 degrees once the secondary bevel is the same size as the primary bevel.
Step 2: Honing
This is the stage where you will begin to produce a 30 degree secondary bevel. In order to avoid wasting material, I recommend doing this on a sharpening stone as opposed to powered sharpening equipment.
Key points to remember
Accuracy of Angle
Same as before: Don't stress if the angle ends up being 28 degrees or even 32 degrees instead of 30 degrees. The chisel will still work just fine. What matters is that you are able to exactly reproduce that angle next time you sharpen.
Keep the secondary bevel small
We want to be able to sharpen the secondary bevel as many times as possible before having to go through the effort of regrinding again. This means you have to be conscious about how much material you are removing when sharpening the secondary bevel.
If you take off too much material when sharpening the secondary bevel, it will not be long until you have to go through the effort of re-grinding to 25 degrees again.
If you don't take off enough material when sharpening the secondary bevel, your chisel will not be sharp. You will find this balance over time so do not stress about it to begin with. It's worth getting your head around though.
How square does your chisel need to be?
The squareness of the edge affects how perpendicular the chisel will rest in relation to the work piece when chiselling. It’s best if its square, it will be unnoticeable if it’s a tiny bit off, but it will be a problem if its majorly out. It comes down to feel at the end of the day and you will figure out your own tolerances very quickly. People often grind chisels out of square due to putting too much pressure on one side of the blade while sharpening, or by clamping it at an angle in the honing guide.
Step 3: Polishing
This stage is optional but makes all the difference in applications where you are paring across endgrain. (Which is most joint cutting operations). I class a polishing stone as above 5000 grit however there is no defined standard for this. If you want to keep the process quick and simple, omit this stage and jump straight to Step 4.
What angle do you polish a chisel at?
You may hear of a tertiary angle being used when polishing which involves raising the chisel by 1 degree in order to focus the cutting pressure right on the edge. In fact, the Veritas Mark II Honing Guide has a setting that allows the user to precisely do this.
While I recognise that producing a tertiary angle is a good method, it's not normally something I bother doing. I just polish the secondary bevel. It's completely up to you though!
What to look for
The polishing is finished when the scratches left by the honing stage have been removed. This is easier said than done for some people. I just recommend using your best judgement and look for a mirror shine to appear. If you’re seeing a dull grey surface on the secondary bevel, it’s likely not polished enough.
Step 4: Flattening the back
After sharpening the bevel, a burr will be produced on the flat side of the chisel. This needs to be removed on the sharpening stone. You will also need to sharpen the back of the blade to the same grade as the secondary bevel. Meaning you may have to go through the coarse, medium and fine grades on the back this time.
Key points to remember:
Ensure your sharpening stone is perfectly flat.
Failing to work on flat equipment will round off the back of the chisel and cause issues when it’s being used, also when it comes to removing the burr next time you sharpen. Waterstones and Oilstones are big culprits for this and require frequent flattening. Good quality Diamond stones or Scary Sharp Sandpaper is less risky and less maintenance in this regard.
Make sure the chisel is perfectly flat on the stone
It's important not to elevate the handle when sharpening; which is much easier said than done. There are two ways I often see this go wrong:
Grasping the handle when flattening: I recommend putting both hands ontop of the blade when flattening it on the stone. Do not hold the handle as this will likely cause you to unintentionally lift it. Hold it with light pressure if you absolutely have to.
The handle contacts the surrounding work surface: This is an unfortunate one that isn't necessarily the students fault. The chisel will look like its flat on the stone, but what they wont realise is that the handle is actually resting on the workbench surrounding the stone and is causing it to be elevated. This is a common issue with Scary Sharp Sandpaper (Mounted on glass) and thin Diamond Stones. It's less of a risk with Water Stones and Oil Stone as these tend to be elevated higher off the work surface.
Is the chisel itself flat?
Sometimes chisels will intentionally have small hollows ground in the back. This is a good thing as it allows the outside edges of the blade to rest on the stone and therefore be stable. If the back of the blade is convex (a bump in the centre) you will face issues when flattening as it will rock side to side. If you purchase a chisel and it has a bump in the centre, send it back as faulty. (But ensure your stone is flat before blaming the chisel!)
Dropping onto the stone or starting from the edge
When removing the burr, you have a choice to drop onto the stone or start from the edge. I was taught to come on from the edge and is the technique I usually employ as it prevents the burr from being crushed under the blade. However I can’t say I’ve done the research to establish if it makes a difference or not.
Step 5: Stropping
After flattening the burr from the back of the blade, there may be remnants that fold back over to the bevel side. Unlike previously, these burrs are often holding on by a thread so they will not need to be ground off using a sharpening stone. However they do need to be removed carefully in order to preserve edge sharpness. A leather strop is ideal for this step. You can even put an abrasive compound on the strop (providing its finer than your polishing stone) and you will polish the blade even further while simultaneously removing the burr. This is the method I tend to employ.
Key points to remember:
Flex in leather
As leather has a level of flex in it compared to normal sharpening stones, it’s possible to freehand this stage as it will conform to the angle of the blade. Providing you get it somewhere near the 30 degree angle of the secondary bevel of course. This saves trying to reset it in the honing guide after taking it out to flatten the back.
Stropping the back
After stropping the bevel, you can also strop the back of the blade. But don’t do it excessively. Doing so may cause the flex of the leather to round over the back of the blade. One or two passes is sufficient.
Step 6: Maintenance
Every cut you take with your chisel is going to dull it even further. Carrying this on for too long is going to severely break down the cutting edge and will take longer to sharpen next time. It may even need to be reground which as you probably know by now, takes a long time!
By staying on top of the blade and sharpening regularly, it will prevent it breaking down excessively and make sharpening as easy as possible. I even go as far as placing a leather strop next to me when chiselling so that I can dress it up after taking a few cuts. While this cant be maintained forever, it does mean that I can get a much longer life out of my chisels and cut down sharpening time to a minimum.
This technique is often employed by carvers who want to ensure their weird and wonderful shaped chisels do not break down excessively. You really don't want to be regrinding those shapes often!
Sharpening is a geometry and numbers game. You need the angles to line up perfectly with one another and you need faces flat against one another. Failure to do this will cause you to contend with rounded faces, unpredictable and inconsistent bevels, and will increase sharpening times and frustration levels drastically.
You also need to factor in the grades of abrasive to your workflow and how they affect the speed and result of your sharpening session. Coarse grades cut quickly and are ideal for regrinding. Fine grades cut slowly but will produce an extremely polished surface.
It’s a lot to take in to begin with, but it soon becomes second nature. I recommend starting off with a cheap honing guide, a coarse and medium stone, and a strop charged with polishing compound. This gives you all the grit ranges required for sharpening, an easy way to setup and retain the angles, and a cost effective method of removing the remaining burr while simultaneously polishing the edge.
Please don't hesitate to drop a comment below telling me what part of this lesson you found the most useful. If you have a different method to the one I have listed above, please share it with everyone! But please keep it constructive and succinct. Sharpening forums have a habit of becoming warzones!