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Edges are examined using an Intel QX3 digital microscope, which was originally sold as a toy for children. Mine cost about $30 on ebay and needed some modification. For more accurate focusing, I removed the body of the microscope and mounted it in a holder with a 28 tpi screw mechanism.
For better illumination of the blade, I have added three high-intensity flashlight bulbs at a distance of about half an inch from the blade edge. The light from these bulbs hits the blade at a low angle from each side and from the back. In addition, a 20 watt halogen desk lamp is used to illuminate the edge from the side.
The blade is held on a jig that can be adjusted to make the face of the bevel perpendicular to the line of sight of the microscope.
Since the pictures below were taken, the blade holder has been rotated 180º and a slide has been added that allows the blade to be moved from side to side in a straight line, making it easier to examine the entire blade edge.
Here are some pictures of the original microscope holder:
Since the most recent modification, the flashlight bulbs shine onto the back of the blade instead of the cutting edge. The light in the microscope body shines onto the cutting edge from the front. I am experimenting with rotating the microscope so that the blade edge is no longer horizontal in the image. This is to eliminate reflections that don’t seem to correspond to the actual condition of the edge.
To give an idea of the scale of the images produced, here are some common objects at the same magnification:
The image sensor in the microscope produces an image that is 352 x 288 pixels in size. The Intel software that comes with the microscope uses a central region of interest that is 320 x 240 pixels, and interpolates that region to produce an image 512 x 384 pixels in size. This larger image always looks a little fuzzy due to the interpolation.
The images on this site have been imported directly into Photoshop at their original 352 x 288 pixel size. Each pixel in the image represents an area of the blade about 3 microns square. Just over 8 pixels are equivalent to .001”.
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