I sharpen my own. My jointer is 12", my planer is 20". It's taken awhile to get there, though. I have one of the Makita sharpeners, and could never get accurate results with it. I told my brother he could have it. I use a modified machine that I bought from Grizzly about 6 or 7 years ago. They don't sell it anymore...not surprised, as it had some flaws. 3450rpm motor for one thing...impossible not to burn the steel, and a slow-drip of machining fluid just got flung around the shop. The knife holder was also heavy and cumbersome to use. Eventually I changed out the motor for a variable speed dc motor from a treadmill and made a steel disk for the business end of the motor shaft. I attach various grit thin grinding wheels to the disk, depending on what shape the knives are in, and if I'm feeling ambitious finish it off with some 600/800 grit sandpaper (a la scary sharp), although this last step is unnecessary for these machines. I also modified the knife holder so it's lighter and easier to use, and did some work flattening and smoothing the two surfaces that slide together. I allocate an entire day for both machines, which includes sharpening 7 knives (3 jointer, 4 planer) and reinstalling and aligning them. If other things also need work (tables, rollers, etc) it can go into a second day. I think most folks consider this a waste of time, and prefer to send the knives out. I like being in control of the process. I like the results I get, so my tendency is to just do it when it's needed and not put it off. Also, my shop is not my livelihood, so spending a day or two on machine maintenance doesn't cut into cash flow.
Cheers.