I believe that Dremel has a jig for sharping blades.

I use a grinder and simple wooden block to get for the angle.

I just bought a Work Sharp. I haven't tried it on mower blades yet (mowing season is over here in the Great White North), but it did wonders on my kitchen knives. They're $70-80 about anywhere

I was at Lowes the other day and there is a sharping jig for the Dremel. I has three jigs in the package, one is for lawn mower blades. It was about $15

The Dremel is a very weak, underpowered tool for grinding mower blades. I'm assuming you have the usual nicks and dings from running into bits of gravel and old dog bones when you mow. The fastest way to grind a mower blade is with an angle grinder (4" or 4 1/2" size) and a grinding disk. You can get a Chinese angle grinder for under $20 at Harbor Freight, and the grinding disks are maybe 2 or 3 bucks. Try to grind at about the same angle as the original bevel. Do it by eye. No need for digital angle indicators--it's not a surgeon's scalpel. When it's sharp, lay a big nail on the end of a post or top of a vise. Lay the blade on the nail so the nail bisects the hole in the blade, crosswise. If it drops to one side, that side is heavy. Grind some more metal off until it's balanced.

As runswithscissors2010: My best experiences have been with the 4" grinders with a soft med - fine grit pad. It works with the blades on or off some equipment. A touch with a fine file adds but not a must.

My 30+ yr old Makita and Black & Decker are hard to beak after 30+ yrs with tons of grinding and cutting vs little but good sharpening. Enough Said For Quality Tools!!