Dog, John, whatever your name is,
I don't know what it is about your responses, but they usually find a way to chap me. Maybe it's your seeming assumption that an Aussie accent makes you the Divine Oracle of all things ovine, but then again, maybe it's just me.
Chad, if you set a comb all the way back in the comb screws, you will _not_ get a cutter set with proper, indeed any, lead. Island Dave's usual excellent description is correct, again as usual. In going on thirty years of using Shearmasters and who knows how many comb and cutter changes, I can honestly say that I have never set or been able to set one all the way back. Probably different in Australia as they use the metric system
Use your eyes, the original lasers, to set your comb parallel to the boss at the base of the comb attachment as per Dave's suggestion. The only thing I have to add is that before you put the whammy to the comb screws, get them snug, set a cutter under the forks, engaged properly in the forks but with only light tension on the cutter. Then, with the machine unplugged, use a slender screwdriver to turn the fan blade, visible through the slots at the front of the motor about half an inch behind the head. This allows you to check the throw of the cutter, making sure it's making it all the way to the last tooth of the comb on BOTH sides. This very useful trick came to me from Charlie Swaim, a former champion shearer and employee of the Oster company. In my opinion, it is the only advantage of the Shearmaster over the Premier 4000, but I have learned to just pop the two screws and pull the head, then turn the gear on the back of the head of my 4000's, accomplishing the same thing albeit in a bit more time. Usually by the time I need a comb and cutter change, I need a break anyway.
As a beginner, most of us spend too much time with the gear in the air rather than in the wool, which means we're running it dry, which dulls it faster. This condition can be helped somewhat by oiling, but not remedied completely. Don't try to shear with dull gear, it will make you old. If your gear won't cut, stop trying until it's sharp. And by all means, if you can, go to shearing school.
Best of luck,