Disclaimer: I've tested this with three different knives without any problems. I have not, however, tested it with the smaller black-top knives. Just to be safe, take a few practice cuts from the safety layer or from a tissue block that you no longer need before cutting actual slides for the doctor.
A side note: If you make really wide OCT mounts (wider than the metal disc), you probably won't get good results with this method. All that excess OCT will dull the adjacent section of the blade and you'll only get two sharp areas of the blade before you have to change it out.
Position #1: Insert the blade just far enough to cut the block.
Position #2: Roughly in the middle. You won't be able to see either of the 2 elliptical holes.
Position #3: Move the blade all the way over until just the tail end of the blade is cutting the block.
Safety Update: In Position #3, notice how there's quite a bit of exposed blade on the left-hand side. You run the risk of cutting yourself, since your left hand is the one that's working inside the machine. I've found that it's safer to take the blade out and flip it over so that the blade looks like Position #1 but with the circular hole on the right side.
If you trim and bevel your tissue blocks and rid them of all excess oct other than a couple of millimeters of edge you can get up to four sections on the blade. I only move enough of the blade so that the "fresh" section will cut into the tissue. It doesn't need to be very sharp to cut OCT since when it is properly frozen has a continuous and uniform consistency. Part of the trouble with cutting tissue is the variability between tissue "geography". The changes between fat, dermis, epi, cartilage etc causes buckling and deformations when cutting so that's when the blade needs to be sharpest to reduce any friction in the cut. Sharper blade = less resistance in cutting. Other things that can affect resistance are: proper machine lubrication, machine temperature, debris in the moving parts, moving parts being properly secured and bolts tightened, beveling of the tissue block (removing spikes, dips and cracks), and finally small bubbles which cause holes around the tissue. Fill those suckers in!
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