How to sharpen the right angle when knifing arises

For the grinding result, in addition to the nature of the grinding tool, the angle at which the blade strikes the abrasive is critical. Even though there are tables, in most cases judgment and skill are indispensable. There is a relatively simple trick to checking the right angle when sharpening.

Two chamfers form two angles

Before sharpening a knife, the existing cut should be considered carefully. Most blade cutters have two grinding steps as seen from the blade mirror. A wider chamfer begins about half way up the blade mirror and runs at a very shallow angle toward the "kinking" second chamfer, the actual cutting edge.

In technical language, the wider upper bevel is called the primary bevel. The cutting edge arises from the secondary bevel. The last piece opens into the microfine, which in turn can, but does not have to, increase the angle value. Here the reduction or elimination of the ridge plays the decisive role.

Blades and chamfer ratio

Another important aspect of sharpening and editing at the optimum angle is the shape of the blade's edge. There are five types of cut that produce a so-called blade geometry:

  • Flat cut
  • Hollow cut
  • Balliger cut
  • Scandinavian cut
  • One-sided cut

With the different types of cut, the size ratios between primary and secondary bevel change. In the case of flat grinding, the primary bevel "kinks" only shortly before the blade edge. The secondary bevel thus receives a higher angle.

The chamfer ratio in hollow grinding is similar, but the primary bevel is dented inwards. This results in less cutting force in the material to be cut due to the smaller displacement mass.

In convex or convex grinding, the bulbous primary chamfer transitions seamlessly into the secondary chamfer. The angle changes fluently according to the rounding.

The Scandinavian cut also has only one chamfer, which runs straight on the blade on a short path on the blade mirror about one-third of the blade width.

The one-sided cut represents half of a flat cut. The two bevels are ground in the same way and the back of the blade remains unpolished. This cut is rarely used on household utility knives and is mainly found on planing knives.

A simple control trick

The challenge in grinding is the consistency of the grinding surface with the machined bevel. Figuratively speaking, the imaginary slope line of the existing cut must be extended. The actual sharpening will, of course, if present, take place at the angle of the secondary bevel.

To control the angle, the secondary bevel of a flat or hollow cut is evenly colored with a dark abrasion-resistant felt-tip pen. The Scandinavian cut marks the entire chamfer. When the blade is pulled over the grindstone, the paint removal indicates the correct or defective sanding angle. If the grinding angle is too flat, color residues remain on the cutting edge, if the cutting edge is set too steeply on the chamfer side in the direction of the blade center.

Tips & Tricks

You should always use a magnifying glass with 80 to 200 magnifications to control your work, so that you can also see the different angles of the chamfers.

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