One of the most dangerous tools is a dull one. A tool with a sharp edge is easier to control in order to get the desired result. All woodworkers need to take the time to develop a sharpening technique and select a sharpening medium that best suits them. This gateway skill is critical to getting the most from your tools and becoming successful in the craft.
The two surfaces of a tool’s blade define the edge and how sharp the tool is. Both surfaces need to be prepared to a sufficient degree to produce a sharp edge. For planes and chisels, preparation of the back of the blade is just as critical to the quality of the edge as the preparation of the front or bevel side; both need attention to get a truly sharp edge. The back of the blade is the reference surface for the tool while in use; as such, it must be flat. Two properly prepared surfaces converge to define the edge necessary for a tool to do its job.
Everyone has a preferred sharpening method and medium. Most media, when used correctly, will allow you to achieve a sharp edge, whether oil stones, a power sharpener, water stones, ceramics, diamonds, abrasive paper or compounds. Find a method that fits your work.
Sharpening may be intimidating to the inexperienced woodworker. With the myriad of jigs and media to choose from, making the right choice can be quite difficult. Sharpening involves three distinct steps with only the last one being used frequently. How to lap, grind and hone the blade are what you need to know to achieve the perfect edge.
Step 1: Lapping the Blade
The first step in sharpening a plane or chisel blade is to ensure the back is properly prepared. This lapping provides the reference surface for the bevel. It is important that the back of the blade is treated with the same grit as the front, with the lowest grit used on each edge to define the quality of that edge.
Most new blades come already sharpened, but factory grinding is no substitute for a proper treatment on a quality sharpening stone. Vintage tools often come with blades that require substantial flattening before use. Regardless of the blade type, the process to lap or flatten a blade remains the same.
It’s not necessary to lap the entire back of a blade; only the section being used needs to be flat. Flattening the first half inch or so of a plane blade will allow for many hundreds of honings before the blade needs to be lapped again. This differs for chisels, which require a completely flat back. Only the last bit near the edge needs the full polishing treatment.
First determine how flat the blade is, by drawing a hash pattern on the back of the blade with a marker; then lap the back with a swirling motion on a flat fine stone, such as a 1200 grit diamond plate or 8000 grit water stone. A couple of passes along the length of the stone is enough for now.
Most new blades need only a small amount of lapping on a fine stone to be flat enough to hone. Blades that show considerable hollows or bumps should be flattened on a coarse stone. Work your way up through the grits to remove the scratches left by the previous grits.
It is important to prepare the back of the blade to the same level as you plan to hone the bevel. If you routinely go to an 8000 or 10000 grit ceramic stone for honing, the back needs to be prepared to at least the same level near the cutting edge. Many suggest preparing the back to the finest stone you have; that is good practice, although not mandatory. Nothing beats that mirror polish on the back of blade showing it has been prepared to the maximum!
Once you have properly prepared the back of the blade through lapping, it is ready to be honed.
If it’s necessary to regrind the primary bevel on a blade to either repair blade damage or to re-establish a fresh bevel for honing, it usually requires coarse grits or power to remove the amount of material necessary to reshape it. The grinding process is complete when you establish a burr (metal lip that forms on the trailing edge of a blade you are grinding) on the entire length of the edge of the bevel. The coarser the grit, the bigger the burr will be as it pushes steel over the edge being ground.
Grinding to remove a nick in the blade can be done on a grinder or a coarse media choice such as a diamond stone or sandpaper. Be sure to keep the blade perpendicular during the process to avoid introducing a skew to the blade.
Grinding is also required to re-establish the primary bevel after the secondary bevel becomes too large to hone. For many woodworkers, this means the bevel may need to be re-ground every 10 –15 honings.
The amount of material to remove with grinding is much greater than with regular honing, so coarse abrasives are the way to go. Power options include purpose-made sharpening set-ups that are efficient at quickly removing the material necessary to achieve a proper bevel. The greatest risk is overheating the blade and losing the temper in the steel. This can happen long before the steel changes color. When the blade becomes too hot to touch, a cooling period is recommended.
Bench grinders can also be used with many options for tool rests and alignment aids to ensure the perfect primary bevel is achieved. In workshops where sharpening happens several times a day, you’ll want an efficient power sharpening solution to minimize time spent on this.
Manual grinding methods use all the same media and fixtures as honing, so this is often the method most woodworkers start out with. Hand methods may be slower, but you’re less likely to damage your blades. These slower methods also offer plenty of chance for correction.
Set the blade in the honing guide on the primary bevel angle setting desired and grind away. The time it takes is related to the coarseness of the media used. If you choose to use a regular stone of around 1,000, it may take a very long time to re-grind the bevel, which is why using a coarser medium is necessary. A coarse diamond plate is one option that can also serve to efficiently flatten water or ceramic stones. A less expensive option is using sandpaper stuck to a flat surface such as glass. Use PSA paper or a quick spray of adhesive to hold the paper in place. Be sure to remove the filings as they accumulate, to keep fresh abrasive exposed.
The size of the grit to use is a tradeoff between speed of removal and how long it takes to remove the scratches produced by very coarse grits. For this reason, the coarsest grit used should be 80 to 100. Be sure to switch to a finer grit when the bevel is close to being finished, which will complete the grinding and remove the extra deep scratches at the same time.
The level of grit to grind the primary bevel is a personal choice, since it is the secondary bevel that actually does the cutting. Remove deep scratches from grinding so as not to interfere with the secondary bevel. It’s often recommended to finish the primary bevel with a minimum of a medium stone, such as a 600 diamond or 1000 grit water or ceramic stone. With the primary bevel established, it’s time to hone the edge.
The third and final step is the establishment of the cutting edge. Honing can be done freehand or using a guide. Freehand sharpening, while quicker, requires regular use and practise to maintain the muscle memory necessary to get optimal results. Use of a honing guide is highly recommended to achieve consistent and repeatable results.
To hone the primary bevel, properly mount the blade in the guide and work up through the grits from coarse to fine. When finished with the finest grit, polish the back on the finest stone to remove the burr. To create a secondary bevel, if wanted, increase the angle slightly and do a few passes on the finest stone. Polish the back of the tool again on the same stone to remove any burr and the tool is ready to go.
Knowing when to hone a blade comes with experience. When a chisel gets harder to slide through end grain or a plane starts to drag a bit while smoothing or jointing a board, you know it’s time for honing.
To help streamline the process, most opt to hone a secondary or micro-bevel on their blades so that you don’t have to regrind the entire primary bevel every time. You can achieve a micro-bevel by increasing the blade’s angle relative to the sharpening medium by a degree or two and polishing just the end of the bevel. By polishing just the first millimetre, an extra fine stone will remove enough material in a few passes to create a very sharp edge. It should require only a few passes to raise a burr on the back of the blade. Once the burr is raised, remove the blade from the guide. Lap the back on the same stone and back to work.
For most plane irons and chisels, you should be able to hone the micro-bevel from 10 to 20 times before it’s necessary to regrind the primary bevel. The wider the micro-bevel becomes, the longer it will take to hone the edge as it will require removing more material each time. A best practice while honing the micro-bevel is to make only enough passes on the stone to raise a burr on the back of the blade. This minimizes the amount of material removed and will extend the number of honings before the primary bevel needs to be reground.
Whether using a micro-bevel or not, the process to hone a blade is the same. Normally honing is done on the finest stone you have; many hone to 8000 grit on ceramic or water stones, which is fine for most woodworking. For working harder woods or those with particularly difficult grain, some hone to a finer grit – 10000 grit or finer – up to even 30000 for an edge on a straight razor. While using these ultra-fine grits yields a sharper edge, indeed bordering on a razor edge, these are much more fragile and will wear quickly during use regardless of material. That’s why it’s often recommended to hone only to the level necessary for the job.
Honing your plane blade to 8000 grit will yield an edge for most planing and chisel work that will be durable enough to provide a reasonable working time. When it’s time for that final smoothing cut with the plane or paring cut with the chisel, it may be worthwhile to move up one more level to get the perfect edge. Always keep in mind that the finest grit used in lapping the back of the blade determines sharpness as much as the bevel of the blade. If you intend to sharpen the bevel to an ultra-fine grit above 10000, the back needs to be lapped on the same stones. Always remember, the perfect edge is the intersection of two fully prepared surfaces.
Place the blade in the honing guide on the angle of the micro-bevel setting. A few passes pulling the blade toward you on the finest stone will develop the burr on the back of the blade showing you that your edge is honed. Remove the blade from the guide, flip it over and lap off the burr from the back of the blade and back to the bench.
With a finely honed blade, you are able to get the most from your tool. Fewer things are more satisfying than the sound of a plane taking a thin shaving with no effort, producing a glass smooth surface. Once you find the suitable techniques and media, you’ll begin to get the most from this age-old craft.