A microtome is a device for slicing very thin cross-sections of stuff, in order to view them under a microscope. Commercial ones are available, but they cost upwards of $50. There is a classic DIY solution, but it involves a piece of old technology — a wooden spool for thread. Outside of antique stores, those aren’t common. Plastic ones tend to be hollow, meaning there’s no guide surface for the razor blade; and the razor is likely to shave the plastic instead of slide across it. Gluing a washer to the plastic spool would address both of those problems. But there is very little gluing surface on the end of a hollow plastic spool.
Lacking a wooden spool, I cut a cube off the end of some scrap 2×2 and bored a slightly-oversize hole through it. Using Gorilla Glue, I attached a flanged nut and a flat washer to opposite ends of the hole. Before the glue set, I used the bolt to center and clamp them over the hole. Gorilla Glue expands 30% as it sets. To avoid permanently gluing the bolt into the body, I carefully removed it after a few minutes. You can see glue in the threads adjacent to the bolt, in the image at right. A few minutes with a wire brush cleaned the bolt threads.
Lastly, I flattened and polished the washer on a lapping plate. The edge of the washer-hole was rough, and glue had expanded out of the hole and onto the surface.
The nut & bolt are 1/4 x 20. One complete turn is 1/20″. So a quarter-turn should be 0.0125″ thin. That, and a fresh razor blade, should make slices thin-enough for a microscope.