This basic skill is often overlooked in wood working. You can’t carve braces or joint a top if your tools are dull. You can buy all manner of sharpening devices and the array of “stuff” can be very confusing to someone starting out. The simple fact is everything can be done with a piece of 1/4″ plate glass and various grades of sandpaper.
To start, there are two basic kinds of sharpening: Hollow grinding and flat grinding. Hollow grinding is the most common. The chisel is held against a wheel with a rest and ground at 25 degree angle (some people prefer a slightly steeper or more shallow angle but 25 works for most things). After the grinding the edge will need to be honed. This is done at about 30 degrees so that you are only working on the very tip of the chisel or plane iron. A word of caution when grinding… you can ruin a chisel by using a cheap grinder that runs at 1750 rpm. If you use this method be sure to use a purpose built grinder that uses a slow speed and with at least a ten inch wheel. Grinders like this can be expensive but if you do a lot of chisel work, they are very good. The Tormek system works well (I don’t own one but have used it) and I expect the Jet slow speed sharpening system would work well too.
These systems are very fast but hollow grinding has one drawback… the very nature of the hollow grind means the cutting edge is also weaker than a flat ground one. Systems that use the flat ground method use various grits of sand paper or wet stones and progress to the final polish all the while maintaining a flat edge. Work Sharp is what I use. It’s less than half the cost of a Tormek but is much slower in getting to the finished product. It is a flat 1/4″ disc with sand paper attached to it that revolves at a slow speed. The chisel or iron is held in jigs to maintain the angle. Both systems require a certain amount of accessories. For example the Work Sharp requires an attachment to sharpen wide plane irons, and the Tormek has a myriad of jigs and contraptions to sharpen every possible item. If my primary job involved lathe turning, this would be my system.
If you are a hobbyist luthier, you don’t need any of this… Just a piece of 1/4″ glass and various grades of sand paper will do. You will have to buy or make a jig to maintain your angle. General and several other companies make such things. Some of the pricier models will cost almost as much as an entire system so take that into consideration. You can also make one. The important thing is to maintain that 25 degree angle.
I start with 100 grit if the chisel is in bad shape. Then progress all the way to 1500. The bevel side is important but no more than the flat back. If a chisel or plane is to work properly it must have a flat back. If it’s not flat it’s a knife! I like to get my chisels to the point where I can see reflections. This is not for vanity but to allow me to make perfect miter cuts on purflings by using the chisel’s mirror image as a guide.
Now a word on chisels and planes themselves. Buy an expensive tool, pay for it once. Buy a cheap tool and you’ll pay for it every time you use it. This old nugget is especially true with chisels and planes.
This doesn’t mean you have to go out and buy a 300 dollar set of German chisels. Marples now Irwin are fine to start. They won’t hold the edge that Two Cherries brand of Lie-Nielson does but the steel is good enough to get you through. Do not under any circumstances buy any of the junk from Home Depot or Harbor Freight. The steel is soft and will not hold an edge. The Japanese chisels are very good as well. They are laminated with a soft steel in the body (very flexible and resilient) and a hard steel for the cutting edge. They also have a hollow back to make flattening easier. This does have the drawback of limiting the chisel’s life, but most people will never have to deal with that.
Planes are a different story. Buy the best you can. Look for good old ones or buy a new Lie-Nielson or Veritas. A 24″ jointer can run almost 500 dollars but it is truly a thing to behold. I know now I’m talking tool porn. You can’t go wrong with a jack plane to start and add more as you go.