There are a few different types of grinders which are suited for different areas of finishing; grinding, sharpening, shaping, removing, and polishing. Below we'll briefly touch on the different types and uses, along with some recommendations for different grinders in order of quality/price efficiency.
Grinding wheels and discs: these are printed with maximum safe operating speed which shouldn't be exceeded (you'll risk destroying the wheel or disc if you do). Wheels vary in grades from coarse to very fine, and vary in hardness, depending on the size of the abrasive grains which make up the wheel.
Bench grinders (pedestal grinder): check the rating with the size of the grinding wheel it takes (make sure you follow the right size ratings). Bench grinders will get your metal hot which makes it useful to stop and dip your metal into a water vessel often throughout your session.
Angle grinders: normally utilized when a bench/pedestal grinder does not fit the bill. Angle grinders use discs instead of wheels, where the face of the disc is used instead of the edge. Because of this, users must be wary of sparks; it's common practice to either wear proper protective gear or set up a guard to redirect/catch the sparks. These takes a little getting used to but generally offer more precision and better shaping/profiling results than bench grinders.
Belt grinders: these are the most expensive but also the most versatile and effective. Similar to the abrasive materials used in the grinding wheels and discs, the belts are coated in abrasive material and run over your desired surface. There are a handful of different types of belt grinders:
Belt grinders can be used for smoothing surface roughness, removing micro burrs, cosmetic marks, polishing, radiusing, edge breaking, high stock removal, cleaning corrosion, removing tool marks, and dimensioning. The following variables allow users to perform these tasks: belt speed, grinding pressure, feed speed, durometer of the contact drum, size of the contact drum and the abrasive belt that is used.
Info: A great economy tool for grinding, sharpening, etc. It has solid construction, strong motor and good features for the price.
Info: Great value, better motor, powerful, sturdy construction, takes a beating well. Comes with a solid case.
Info: Very powerful, effecient, longlasting and durable angle grinder with effective dustry protection and air injection.
Info: 1 inch wide belt surface, ideal for sanding/sharpening metals, wood, plastics and composites. The Baldor 1/3hp direct drive motor is strong enough for demanding jobs. An all around effeciently priced and quality belt for working on small-medium sized projects.
Info: Allows for sanding, grinding or finishing of outside curves or odd shaped workpieces on the belt. Deluxe miter gauge that turns and locks for common angles 45° both left and right. This is a powerful machine with versatile, longlasting usage.
Info: A versatile, durable, longlasting and effective grinder for most general work. As reviewers point out, the tracking is not great but will allow new-intermediate bladesmiths to make good knives.
Info: Good value for the pirce. Powerful 3/4 hp induction motor provides steady power for industrial grinding applications. Well balanced and runs smoothly. Guards are decent but some reviewers point out they could be better.