I'm about ready to make a call for the group buy deal but have a question on the grinding wheel wear. I currently have a Oregon red wheeled blade sharpener. Owned it for 3 years and never have needed to replace a grinding wheel. The current dia is 7.5" and don't remember what it started out as. I started not using it much (a set a week) but now I'm doing 3 sets a week so trying to cut my time down. I read about people using up grinding wheels a lot on the Magna-Matic. I hear after the initial sharpening it doesn't use as much wheel though. So my question is how many sets of 61" blades can a person do on a wheel? I know it has a lot of variables in the question but a educated guess would be nice to know. A wheel is $30 so it's not much but worth knowing.