I going to try to explain a little about grinding wheels, what makes one more efficient than others, what to look for before purchasing, which grinding wheel best fits you particular style of grinding, and the cost differences that might steer you toward a different wheel type.
Grinding wheels are composed of a couple of things, abrasive granules, and bonding agent. These wheels contain thousands upon thousands of abrasive granules, each of which displays many cutting edges. Selecting a grinding wheel with the correct bonding agent and abrasive granule type for your application can be difficult. When you find the best wheel for your application it will be able to constantly sharpen itself by granule fracturing and granule release without burning the steel.
To select the best grinding wheel for your particular application, a good understanding of the composite of the wheel is needed. A combination of abrasive type, abrasive grit size, hardness grade, granule structure, and bonding agent determines wheel performance. By varying the amount and type of each of these elements, the effectiveness of the wheel can be made to respond differently.
The abrasive granules are the elements of the grinding wheel that actually cuts the moulding knife steel or carbide from the knife blanks. Here are four abrasive types that we commonly use in our industry; Aluminum Oxide, Ceramic, Cubic Boron Nitride (CBN), and Diamond (for carbide), I prefer a ceramic blend grinding wheel for rough grinding high speed steel and the “Mirror Reflections” 2mm Ultimate 125% concentration 120 grit, 10mm of borazon grinding wheel for finish grinding.
All abrasive granules are sized to an established worldwide standard and are designated as a numerical grit size, the larger the number, the smaller the granule size. Generally speaking a large number or coarse granule size will increase stock removal rate, but provide a poor surface quality finish. High number granule sizes provide less steel or carbide removal, but vastly improve surface finish quality. Most grinding wheel manufacturers utilize combinations of two or more grit sizes to produce various finishing effects for each grinding step.
Hardness grades for wheels are designated by letter “A” (softer) thru “Z” (harder). This letter grade represents the specific amount of bonding agent contained in the wheel which determines the ability to hold the abrasive granule in the wheel. Normally, the harder the grade the better surface quality you will obtain, but it provides a smaller chip removal rate than softer grades, which can lead to burning of the tool.
The granule structure of a grinding wheel refers to granule spacing within the wheel. This granule density is identified by a number 1 thru 16. The more open the structure within the wheel, the higher the number is designated. A denser wheel will generally provide a better finish, but will generate more heat and again a slower metal removal than a more open structure wheel. So to sum up what we have discussed so far, I would recommend 54 - 60 grit wheels for roughing out the main portion of the moulding knives blanks and a 100 – 120 grit wheel for the finishing portion of the procedure.
We continue with the grinding wheel bonding agent or binder which is the material that holds the abrasive grain together. Here are a few essential properties of the best bonding agents. The binding agent must have the ability to retain the grain during grinding, self-sharpening and dressing application. It must also have the ability to allow the grain to be pulled out from the grinding wheel when the grinding friction becomes high because the abrasive grain has become too dull to properly cut. Here are a few types of bonding agents that are common to our industry.
For the woodworking industry, the large majority of grinding wheels used are either ceramic or aluminum oxide abrasive with a vitrified bond. Within each category, there are numerous different types of ceramic, aluminum oxide, and bond types that can be used depending upon the manufacturer.
You now realize the proper grinding wheel selection is not easy. Each change made in any of the elements within the grinding wheel affects the others and can react in different ways. Some other things must also be factored in to determine the best grinding wheel for your application, including the type of steel being ground, type of grinder being used, and the grinding techniques of the individual operator.
We have a large selection grinding wheels for both rough and finish grinding moulder knives, located in either catalog under “Tooling & Supplies” tab above.