One of the most common problems we encounter with microtomes is over lubrication. Many users seem to think that if three drops of oil are called for, then six or seven or even twenty must be better. The problem with this is that oil mixed with paraffin (Microtomes make excellent mixers!) makes a viscous gel that prevents components from tightening against one another. For example the cam in a knife holder can no longer lock against its proper bearing surface, resulting in thick/thin sections.
The key to good microtome maintenance is cleanliness and minimum lubrication. When you are done cutting for the day, remove your knife and then take the knife holder off the machine. Brush the machine off, paying particular attention to the specimen holder. After cleaning the specimen holder, check its function: Is the paddle loose? Can you twist or rotate the paddle? If so, you need to contact someone for repair. A loose paddle can slip, causing a very nasty cut! Now, engage the brake and make sure it works. With the brake on it should be significantly harder to turn the cutting handle. If not, call for service. Note that it is often possible to turn the handle even with the brake on. It’s a question of degree: Is it harder to turn the handle with the brake on? If so things are probably ok. Now flip the brake off. (No, not like that!) Does the specimen holder drift down? If yes, the timing is bad and you need service.
Check and make sure the knife holder clamp (the clamp that holds the knife holder in place) moves freely up and down. If not put two drops of oil on it and work it up and down. If it doesn’t free-up, call us.
Check again and make sure the knife is out and then disassemble the knife holder. When I do this I lay all the parts out, in order, in front of me. This simplifies assembly. Clean the locking cams.
Remove and clean under the pressure plate. Caution! Be careful that you don’t loose (as in “Ping!”) the pressure plate springs!
Run your fingernail across the top of the front and rear pressure plate. If your nail catches or you feel dings, replace the plate. Clean all the grooves on the knife holder base, a cotton swabbed stick simplifies this.
Put 2-3 oil drops on each cam and reassemble the knife holder. On Leica machines, set the cutting angle at 4-5 degrees, and place the knife holder back on the microtome.
Your microtome should now be ready to go back to work. Happy cutting!