It will come as no surprise to you Stephen that sharpening an end mill is done in two stages, sharpening the end edges and sharpening the side edges, though not necessarily in any particular order. However, in most machining tasks the two edges perform different tasks. The end cutting edges predominantly determine the surface finish whilst the sides remove most of the metal.
Contrary to Ron's findings, I frequently only sharpen the ends achieving a very noticeable improvement to the finish achived. If the side edges though are less than sharp this only places more load onto the machine which can be compensated for by taking a shallower cut. Here we are talking say 6mm rather than 8mm, it not being a consideration for light surfacing cuts.
If the side edges are to be used to surface the edges of a workpiece then in most setups the end nearest the shank can be used for the purpose as this will unlikely to have been used to cut metal. It may of course have lost a little of its edge due to careless storage.
As the end edges are only called upon to cut over a very short distance at the outer diameter, being equal to the feed per tooth, say 0.05mm, sharpening them is far from critical. The two important factors being that the end faces must all be at the same level and must produce a very slightly concave result. The latter so that the cutter only cuts on its tip even if the machine spindle is minutely off perpendicular to the table's traverse.
Because of the above, sharpening the end faces can be done with very simple equipment as in its simplest form the cutter only needs to be plunged into the wheels surface. Rather than attempt to describe a method can I suggest viewing my
website
Sharpening the sides is though, by comparison, much more involved, again can I suggest another page on my website which uses a device, much like that shown by Chuck and a grinding table to control its position. See
here
The grinding rest has been extensively discussed elsewhere on this forum
here
I would suggest Stephen that you first choose, say 10 end mills, and using a simple set up sharpen their end faces and determine how they work when put to use. From there, you can decide if you wish to go further with obtaining/making the move involved equipment for the side faces.
Harold Hall