Grinding

Knives, that is. I don't do skateboards.

I'm going to cover some basic stuff on this that I've picked up over time, and cover buffing later. I will tell you this right now; this part can be DANGEROUS, and I'm not joking. You just cannot take chances with this, the stuff will bite you. Badly.

The most basic is files, which come in all sizes and shapes and roughness of cut. A double-cut bastard file will take metal off faster than you might think, but it still takes a while. It can be done; a few years ago Knives Illustrated magazine had an article on a maker from the former East Germany who did everything with files. Rough-shaping, cutting the bevels to the edge, shaping the guard and pommel and grip. He polished by wrapping finer & finer sandpaper around a file to clean up the finish, and his work was beautiful. He had no choice in the matter, in East Germany there had been no other tools available, but his work shows that it can be done.

Next step up is a bench grinder. Basically an electric motor with a long shaft sticking out of each end onto which is held a grinding wheel. With a coarse wheel you can remove a lot of metal fast, with a finer wheel you can rough in the bevels, clean up the profile, etc. If you're careful, you can hollow-grind a blade on one. They're very useful, but you have to watch a few things.
First, you have to get a dressing tool. The wheels get uneven with wear, and the tool lets you even it up. You can also use it to round the corners or shape a wheel in different ways to do specific jobs.
Second, there are two hazards with these. First is the most obvious, that if you slip and push your hand into the wheel, it WILL HURT. Bad. There may be lots of bleeding and swearing, and people have permanently injured themselves with these. Second is the wheels, if damaged, can shatter. If you have the guards and covers in place, this will generally just scare hell out of you. If you've taken the guards and covers off to get better access to the sides of the wheel and different angles of grinding, this is damn near the equivalent of a grenade going off. The shaft of one of these is generally turning a couple of thousand rpm, which means that the edge of the wheel is turning a fast, and if a damaged or faulty wheel shatters, pieces fly at high speed. I've never had it happen; I know of people who have been badly hurt when it hit them.
I'll hit other general safety stuff at the end.

A step up is a belt sander. I bought a 6x48" belt sander, which also has a 9" disk sander on the side, years ago and I've used it for a all kinds of things. I normally flat-grind my blades, and this is great for that, especially long pieces. You've got a big work surface, you can get belts from 40 grit to 400 so you can do rough grinding all the way to finished. You can get a nice unit for a couple of hundred dollars new, and if you take care of it it'll last for years of hard use. To hold long pieces, some tool supply places sell magnetic holding tools that allow you to keep control of a long piece without burning yourself on it. It's a great all-around tool. Bad things are
First, you can only flat-grind. There's no good way to hollow grind on the pulleys, and no way to change them out to different sizes.
Second, it will hurt you if you slip. A belt can't shatter like a grinding wheel. It will tear you up just as bad if your hand or arm or elbow slips into it. The edge of a moving belt can slice you. And if you get your hand or finger pushed into the belt for more than a second, it not only eats skin and muscle and anything else not taken away fast enough, it can actually burn you while it does it. With this and the next item, people have been sent to the hospital for serious repair work.

The last is the belt grinder. There are a number of brands, and most use a 2x72" belt(there are smaller ones for lighter work). These are the Cadillac of grinders. They're made to grind metal, you can change the contact wheels to different sizes, you can profile a wheel to give a certain grind, you can use a platform to flat-grind, and you can get belts from very coarse to finer than 1000 grit. They're marvelous machines, very versitile. And they cost. Last time I looked at them, the good ones ran about a thousand for the basic setup. Start adding different contact wheels, etc., and it goes up fast. If you were going to go heavily into knifemaking they're worth the money. All cautions of the previous grinder apply.

Many makers will have all three of these. You can do the heavy work on stock with the bench grinder, use the 6x48" for flats, the 2x72" for finishing. Or some combination thereof. If you've got the money you can do all of it with a good belt sander, and the 2x72" units will do all kinds of stuff.

Warnings:
Especially with a bench grinder, some kind of eye protection. Sparks, dust, bits of wheel, all of it goes flying. Take some of that in the eye, you've got a problem. It's a good idea to wear it with any of these.
Lung protection. All three of these put out a lot of dust, and you don't want to inhale it. Metal is bad enough, but when sanding some woods, particularly some tropical hardwoods, it's worse: they're actually toxic. Ebony and cocobolo are two of the worst, they'll make your skin itch(especially if you're sweating), and they can do a job on your lungs; so will some synthetics like pakkawood. A dust mask or some kind of respirator is advised. Strongly. A lot of pros have a vacuum system set up with an inlet at each tool to suck up most of it, and they still wear a mask.
Fire. If you let a lot of dust accumulate, it's a definate fire hazard. Wood dust, metal dust, epoxy dust, leather, if it builds up it can be a problem. A shop vac is a very handy tool.

This is, again, a basic on this. If I remember something else about them, I'll add it in.