Blade grinding

In order to turn a forged steel billet into a knife blade, you need to grind it. Grinding is mechanical shaping of the steel, using files tools or other abrasives, into a functional blade. Often, the word “grinding”, in a narrow sense, means adding an edge to the blade, and “grind” refers to the style of cutting edge. However, in a general sense, the “grind” of the blade refers to the overall cross-section of the blade, not the actual style of cutting edge. 

Technically, grinding is a sub-set of cutting. It uses abrasive wheels as the cutting tool. Abrasive grains on the wheel gradually remove tiny chips of metal from the blade. The process is similar to other metalworking machining processes, only that here metal is being removed on a much finer scale. Rough grinding done with low grit sand belts scratches out large amounts of material rapidly – this is needed to shape the profile of a blade. Finer grinding with high grits is used to produce bevel grinds and fine finishes on the blade.

The grind is what makes a knife a serviceable cutting tool. All true knife adorers have to realize how the grind impacts the use of a knife. The shape of blade’s cross-section, the slope of the steel towards the edge, are paramount in defining knife’s cutting ability, edge retention and endurance. The grind determines how you’ll need to operate, sharpen and maintain your knife. A grind good for miniature slicing operations will not do for rough chopping, and vice versa. When choosing a knife, it is important to make sure you get the right blade grind according to your intended use; otherwise, the wrong knife grind will impair the purpose of your knife.

Grinding can be divided into two categories: grinding the blade profile and grinding the blade’s edge.

Grinding the blade profile

After a blade has been forged, it needs to be cut to an exact shape of the knife profile, which can be done with a variety of tools, such as steel shears, cut-off wheel, or a grinder. Unlike honing and polishing, grinding the knife profile will remove considerable portions of metal from the blade. Grinding is done prior to heat treating, so you needn’t worry about heating up the metal with friction at this stage. 

Blades can be processed with grinding not only at the stage of shaping the profile, but also after a significant damage, such as broken tip, chipping, or corrosion. If you maintain your knife properly, it will require grinding less frequently. On the contrary, if you neglect your knife, subject it to aggressive environment or rough handling it is not designed for, you’ll need to repair a broken or deteriorated blade by newly grinding it.

When you’re grinding a blade profile, you are removing the excess metal from the billet to produce the profile you’ve designed for your knife. A cut-off wheel or a hacksaw will be a lot of work, so it’s better to use a grinder that will do the cutting and shaping smoothly and quickly. A belt grinder or a surface grinder will easily cut the blade into its proper shape, finely flatten the edge and remove any scratches or burr.

After grinding the profile, the blade should be at 95% of its final shape. The remaining 5% will be removed during the final polishing stage.

Grinding the edge bevels

The knife’s intended purpose, that is how you’re going to use and maintain your knife, would define the proper grind. Big varieties of knife grinds offer various blade’s cross-sections that will impart different qualities to the knife blade. When a lot of material is removed from the blade, it will become thinner, and hence, sharper. But, such a blade will dull faster. On the contrary, a thicker blade will be more durable and will retain an edge for longer, but will not be as sharp as a thin blade. Depending on the intended use, some blades are thicker and sturdier, some are thinner and sharper, and some try to find a balance between the two extremes. In addition, the strength of a cutting tool is not ultimately determined by grinding. Expert knifemakers know that, while the grind is important, it is, basically, the width of the blade stock, the material used, and the grind angle that affect the strength of the blade most. 

It is well known that there is always the compromise between the blade’s ability to take an edge and its ability to retain it. Some grinds – for instance, convex – are easier to maintain, while others – like hollow grind – retain their integrity with difficulty. Type of metal also matters: a harder steel will take and keep sharper edges, but being more brittle, will chip more easily. On the contrary, a softer steel is tougher: its sturdy edge will not be prone to chipping or cracking, but will not be as sharp and will require more frequent grinding. 

Your intended purpose will define the blade grind you’ll be looking for. If you’re about to get a knife for skinning or similar slicing jobs, the hollow grind will do fine, as its razor-sharp edge will suit for such operations perfectly. If you need a knife that must be tough but not require a very sharp edge – for example, a cleaver or a survival knife intended for rough use – you’ll be likely looking for the V-grind (“Scandi”) or the convex grind. In terms of material properties, the relation between hardness and toughness of metal is often complicated, and some metals manage to combine high hardness with great toughness in one alloy.

When you start your grinding machine, be careful, as this is probably the most delicate step in building your knife. Prepare sandpaper in several grits starting at 60 grit. It is necessary to monitor how you stand and how exactly you move the blade along the abrasive strip. Typically, you should uniformly grind a slope to the middle of the blade. Then process the other edge in the same manner. Use the grinder to work accurately each edge in a flowing manner to make it excellently straight and smooth. Sequentially apply higher grits to provide a finer polish of the blade.