Blade sharpening is quite an art, its not just about grinding a bit of metal away to make the blades sharp again! At Clippersharp we use several techniques, but the one most commonly used is called "lapping". This is a precision way of taking a very even layer of metal off leaving the blades with a fresh cutting surface.
Because it is a gentle procedure, it not only gives a very accurate finish but also takes an absolute minimum of metal from the blades, which will then in turn, ensure the blades will last a lot longer. By the more rough way of grinding, this leaves more room for error as it is not that accurate as it is done by hand and eye, but also takes a lot more of the metal away too. It also means that blades are not sharpened always on a flat surface which in turn, will leave an uneven finish, and will cause the blades not to work efficiently or even appear blunt when they have just come back from being sharpened.
We can always tell when a blade has been sharpened this way as it takes us so much longer to rectify the blade and get it back to the right cutting surface.
We always recommend, particularly with the larger blades that are used for horses and cattle, to have them sharpened by the lapping method. Lister also recommend this procedure for their make of blades, as they are expensive to replace if they have been sharpened incorrectly.