I have a Troy-Bilt 10HP chipper-shredded and just bought new blades for the chipper, that I'll install next weekend. My question is, can the old ones be sharpened? If so, can I do it on my bench grinder? It appears to be merely a pair of blocks that have one edge ground onto them. At $49/$79 pair replacement it would be nice if I could sharpen and get at least one more use out of them.