The first step in shaping an edge is determining how much material needs to be removed from the knife. A blade that has not been abused, and appears to be very close to its original dimensions, should not require much removal. Alternatively, a knife that has been heavily used, is misshapen, and has been sharpened many times, will usually require the removal of substantially more material to achieve a properly shaped edge.
The first and most aggressive step in our sharpening process is called ‘hollow grinding’. Hollow grinding is a thinning process that simultaneously removes steel from both sides of a blade, and brings the blade into the proper thickness in preparation for edging. Most knife rental companies use hollow grinding in the sharpening process; this is in part because it saves a lot of time in the edging process, but also because many of the knives that are used by knife exchange services are left relatively thick in the manufacturing process. Hollow grinding is water-cooled to retain the temper of the steel. If the temper is lost, the integrity of the steel is lost, and no matter how well the edge is shaped, it will not be durable.
The blade is inserted and ground between two spinning, circular 40 grit grind stones. Hollow grinding requires skill to ensure that material is removed consistently and at an adequate rate along the length of the blade. After a blade has been hollow ground to the proper thickness, it is ready to be edged.
The ‘edging’ process at PostKnife is achieved by free-hand flat grinding on a stand-up grindstone. This is the traditional method of edging that has been used in our family knife service for four generations. The grindstone is 60 grit, and starts off at a diameter of 36 inches; this stone is often referred to as a ‘big wheel’, or the moleta. With water cooling the blade, the blade is held flat and drawn from heel to tip across the grindstone. Knowing which angle to grind a particular knife requires skill and experience. Different knives are sharpened to perform different jobs, which is an important consideration when shaping an edge.
While edging, a ‘burr’ or ‘wire edge’ forms at the very ‘front edge’ of the knife. The burr is excess material that must be removed later in the sharpening process. A stand-up grind stone can efficiently shape a precision edge on the vast majority of knives and blades, however, grinding with this equipment is a skill, and the operator must be experienced to use it effectively. To be skilled at grinding, one must grind thousands of knives, and even then, some people will not acquire the ability to do it properly. An unskilled operator can do irreparable damage to a knife.
Many other knife rental and knife exchange services use an edging machine in their processes to shape the edge. An edging machine can shape a very sharp edge, but a hand shaped edge done by a highly skilled craftsman will be superior. An edging machine relies on the blade being extremely thin in order to shape its edge, and the excessive thinning leads to an edge that deteriorates rapidly.
Once the edge has been shaped, we move on to the buffing wheel. Buffing removes some of the deeper grinding marks/scratches, helps de-burr the edge, and contributes to shaping a finer edge overall. Buffing can be used to improve the blade cosmetically, and later in the process can be employed using finer grits (2k, 5k, 10k, 30k, grease buff, etc.) to achieve a finer finish.
The final step in our knife sharpening process is honing. Some knives are honed by hand on a flat stone while others can be finished in a honing machine. Honing is the least aggressive step in the process with stones at 440 grit. The burr which is created by shaping the edge, is completely removed while honing, and the result is a durable yet fine, razor sharp edge.
ConclusionAnd voila! You have a sharp knife. If you have any more questions about our commercial knife rental service, or any of our sharp knife subscriptions, check out our website at www.postknife.com.