I recently got a router and a set of Freud carbide router bits. I had a friend tell me that he sharpens his bits after every use. So I have a few closely related questions:
I have never sharpened my router bits (they are all the nice ones with the carbide cutters). However, pitch will develop on them after some use. I just use a bit cleaning solution I got from Woodcraft (I am sure you can use cheaper alternatives with the same result) and a brass brush to clean the pitch off. Make sure you use a brass brush and not a steel brush as the brass won't damage the cutters.
Sharpening bits after every use sounds like a really bad advice.
Not only is the router bit getting smaller every time (no joke!), so eventually you will notice that this 6mm plywood that you're trying to stick into the 6mm groove made with your 6mm dado bit wont't fit for some weird reason.
Also you may eventually notice that those identical pieces that you make with the copying ring have a different size than the ones you made half a year ago, for some unexplainable, weird reason.
More importantly, however, sharpening router bits -- like everything related to routers -- is a non-trivial thing which must be done with skill and great care.
A router bit is not comparable to a kitchen knife or a chisel. If you have to ask what tools you need, you do not have the necessary skill to sharpen a router bit.
A router is a considerably strong motor that spins with 24.000 RPM, and most certainly a machine that the intelligent woodworker will treat with due respect. In the context of router, words like "unbalance" are equivalent to any or all of "ruined work, desaster, mutilation, death".
It is therefore a common advice to be most pedantic about very carefully cleaning your router bits (with petroleum and a brush) and to very carefully examine them, but to do no more than at most a few pulls (if at all) over a fine honing stone from time to time, and to either have the bit professionally sharpened after doing that 4-5 times, or replacing it alltogether. (See e.g. Guido Henn's router book).
I think the answer to the question of when to sharpen a router bit is that you look for burning on the material that you are routing. If you see burn marks, that indicates a problem. Clean them first and run another stick through and if it still burns, you need to sharpen.
As to how, I've never actually done it. My carbide bits still work well but then I don't use them very often. If I wanted to sharpen one, I'd start with one of the diamond-encrusted paddles that are sold as "pocket sharpening stones." Here is one example:
With regard to cleaning high speed woodworking tools such as saw blades and router bits, common oven cleaner works extremely well and is very inexpensive. Spray the tool, scrub with a Scotch Brite if necessary, rinse in water and dry completely. Apply a lite aerosol lubricant.
