Others bonding systems serve specific purposes, but are unlikely to be needed in the home shop for the most part. Resinoid parting wheels can be an exception. Other types of bond include silicate, rubber and shellac.
Abrasive designation type within a media is an indication of the process used to produce the media. One might expect to see markings such as 19A, 32A 0r 38A on a Norton wheel. All are aluminum oxide wheels, although each is better suited to different types of grinding. The 38A abrasive has excellent friability and a porous nature, making it the wheel of choice for heavy stock removal and a good choice for HSS grinding.
Assuming one was to order a Norton wheel for grinding HSS, a designation such as 38A60H8VBE would be considered an acceptable wheel. Grinding techniques vary, so some may prefer a slightly harder wheel, so experimentation would be encouraged.
Grinding wheels should always be given a "ring" test before mounting, immediately after a physical examination in which one looks for signs of cracking or pieces having been broken from the wheel. By placing the wheel on a solid object (screw driver, for example), and tapping the wheel with the likes of the handle of another screwdriver, a distinctive ring should be heard. If not, the wheel should be immediately destroyed to avoid an innocent party from mounting what is very likely a wheel that will explode when spooled up. It should be the policy of anyone running a grinder to destroy damaged wheels immediately.
Once it has been ascertained that the wheel is in good health, it should be mounted without a struggle on the arbor. If the wheel is a force fit, a risk of cracking is ever present, particularly when the flanges are tightened, so make sure the wheel fits properly, and can shoulder against the fixed flange (if so equipped) readily.
A wheel that has a bore out of perpendicular with the sides can be cracked when tightened. Should one encounter such a wheel, the bore can usually be scraped adequately to permit proper seating. It should never be horsed.
Always stand aside when spooling up a wheel, even one that is known to be good. The first few moments should serve to shake out a wheel with problems, so allow about a minute of full speed operation before standing in line with it's rotation. That's particularly important in a shop where children have access, or objects are moved about, where reasonable risk of cracking a wheel exists.
Proper dressing of grinding wheels is key to success. Wheels that don't run true and are not relatively flat are useless for tool grinding. You should be able to rest the tool being ground on a wheel and have it stay where placed, without bouncing away. The wheel should be trued immediately upon installation, then dressed on a regular basis as it's being used. One might dress the wheel several times in the process of grinding one tool, but the benefit of keeping the wheel properly dressed pays serious benefits in cooler grinding and faster stock removal. It becomes evident that a wheel needs dressing, particularly if it's too hard.
Truing a wheel can best be accomplished with a mounted diamond, or diamond cluster, but a wheel so prepared is not well suited to offhand grinding. Diamonds tend to leave a wheel quite smooth, increasing area in contact with the grind, and behaving somewhat like a bearing. Grinding with a wheel so dressed tends to be slow and hot. In order to disrupt this pattern, roughing the surface by different means is normal procedure.
The best possible surface for hand grinding is achieved by the use of a star, or impact, type dresser. They function by hammering the wheel and dislodging the old bits of abrasive, exposing new bits that are sharp and ready to grind. Problem is, this type of dresser requires a bit of skill to apply successfully, and often wastes a good amount of useful wheel as the user attempts to get the wheel running true and flat. As a result, I do not use, nor endorse such a dressing tool. Further, if you use the same method of tool grinding that I do (no tool rest), there is no place for the dressing tool to rest as it's applied.
There are available on the market items known as dressing sticks. Two varieties should be of interest for those that intend to grind HSS tools. One is a solid boron carbide stick, typically 3/16" thick, ½" wide, and 3" long. They are excellent for dressing wheels when new, but as the corners slowly round off, they begin dulling the wheel more than dressing---so I don't recommend one unless you have the ability to keep it sharp.
The next choice, and the one I recommend highly, is the use of a vitrified silicon carbide stick. They are typically 1" square and 6" long, and inexpensive (roughly $10). They are readily available from machine shop supply sources. One should last the average home shop type for a life time. Choose one that is coarse grained, anything from 16 grit up to 24, depending on availability. Avoid finer sticks. A wheel, once diamond dressed, can be fine tuned with such a stick in seconds, and done freehand without the use of a rest. It is also applied when redressing is required, keeping the wheel flat and sharp.
