The main problem when using the microscope to inspect knife blades before/after sharpening is that metal is naturally reflective, and operates like a mirror rather than scattering light. That means that it is not sufficient to point the built-in lights at the blade to properly illuminate its surface. Instead it is necessary to provide incoming light from as many direction as practical.

This model implements a reflector that mounts on top of the A (12mm) lens of the Andonstar AD246S-M microscope (and equivalents), and concentrates the light emitted by the stock lights onto the part of the blade under the lens.

Printing & Assembly

Print the part from black filament to avoid the need to paint certain areas black. The provided profile uses support filament to produce the best possible surface.

After removing supports sand the inside of the reflectors to make the surface as smooth as possible. Scraping the support scars with an exacto #10 blade can help speed things up.

Apply aluminium foil to the inside of the reflectors. Use slow setting glue (e.g. slightly diluted PVA) to have enough time to thoroughly smooth the foil out using cotton swabs and q-tips. Carefully trim the excess foil - it is especially important to clean the area around the lens hole to expose the black plastic, as this black area provides contrast.

Finally, use permanent markers to apply contrasting highlights in the area shown on photos. The red color is supposed to reflect from rounded dull sections of the cutting edge, while a burr might catch some blue. It helps to use short dabs rather than long strokes to deposit sufficient paint, and you can try applying a second coat after the first one thoroughly dries if the first one is not saturated enough.

Usage

Due to the optical properties of an elliptical reflector, from the point of view of the part of the blade in the focus of the lens the entire surface of the foil coated reflector directly reflects the lamp. Since the reflector wraps around the blade, any part of the metal surface sufficiently angled to reflect a part of the foil rather than the middle plastic black area will likewise strongly reflect the light.

The reflector is designed for focus distances around the minimum range (i.e. max magnification). Angle the microscope to match the bevel angle so that the view direction is perpendicular to the metal surface.