There are many different answers depending on whom you ask. There is no one correct answer. Some advocate slow speed or wet grinders, some oil stones or waterstones and some the fairly new diamond sharpeners. The truth is that with a standard bench grinder, fitted with an 80grit (white) aluminum oxide wheel and with some practice most woodturners can put an acceptable edge on their tools. Do not use the standard grey wheel that comes with most grinders as it will glaze over very quickly and heat the tools. If you have damaged a tool or feel the need to significantly re-shape it you will need to use a coarser 36 grit wheel. Remember to dress the wheel with a devil stone, star wheel or diamond dresser to avoid forming a groove in the wheel as this will adversely effect the grinding of skew chisels and parting tools.
Should I try to sharpen freehand or use a jig? With practice most turners could manage without a jig but many people do not want to grind away an expensive tool practicing so a jig is the sensible and efficient option. There are almost as many different jigs available as there are grinders. Many sharpening tools such as the Worksharp Sharpening System 3000 allows turners of any skill level to put consistent accurate grinds on their tools. It is easy to set to the majority of bench grinders and you do not need a high degree of skill to use it. It will eliminate at a stroke those facets, which may be created by freehand sharpening. Many turners now prefer a fingernail profile on their spindle and bowl gouges - it is also known as a Celtic or Irish grind. This is very difficult to achieve free-hand.
Whichever method you use remember to keep your tools sharp, try to achieve one consistent bevel which makes for easier tool control and most of all enjoy you turning. The key to successful sharpening is little and often.
