RepRap: Blog

The amount of resin that clings to the surface of the probe is quite small. In this particular case, too small. Most people envisage a hanging droplet, but that's not what happens. First off, the effects of gravity are minuscule on this scale compared to molecular attraction, so things don't hang like you'd expect. Secondly, this is a capillary effect and only the last 100μm or so of the probe has anything on it. Here is a micrograph of Probe 7 before and after dipping in a film of resin:

You'd be forgiven for thinking there is no resin on the probe at all. But if you look very carefully you will see a slight bulge where the distal taper starts. That's the resin loaded on the probe tip. Compared to the area of the point of contact, that's enough resin to deposit several dots per dip in the resin reservoir. This particular probe managed a whole 4 dots but I have had up to 30. This is not enough for our 30-40μm target, so we'll make another probe. I really want something between this and the rounded probe we got with nitric acid. Preferably with that really irregular surface on the sides.

Welcome to the weird world of tiny. 

By the way, this is how I position things at odd angles under the trinocular microscope. I use 10 gram 9mm lead bullets with sticky wax on their bases and a piece of perforated acrylic sheet  that can be moved around underneath the microscope without disturbing the pile of bits. Works remarkably well.