RepRap: Blog

The plan was to make Probe 9 out of 0.13mm dia Nicrome 80 but that cut through very, very quickly at the meniscus when I tried etching it in nitric acid. Probably because I didn't dip it in far enough (my discoveries on etching dynamics are for a later post). Change of plan.

A length of 0.3mm dia 316 Stainless wire was immersed in the 0.5% nitric acid probe etching cell by approximately 10mm, and electrolysed for approximately one minute. The wire was checked twice, and etching was stopped when a noticeable tip had formed. By this time the sides of the wires were roughened.

The wire was then taken to a second cell containing a 5% sodium chloride solution with 0.5% hydrochloric acid. The wire was connected to the anode as usual. The very tip of the wire was then touched to the surface of the electrolyte in the cell for approximately 5 seconds, then examined under a microscope. This was repeated three times. When the probe tip had acquired the desired ogival point, the probe was washed with water, then isopropyl alcohol.

The tip was mounted in the RepRapMicron V0.05 Probe Tip Arm with cyanoacrylate adhesive. A micrograph was taken, the Probe Tip Arm was fitted to the μRepRap, the tip dipped in approximately 0.5mm of "Top Coat" resin, and another micrograph taken:

At this stage it can be seen that the roughened shaft of the probe holds a significant quantity of resin, and that fluid effects (capillary action, surface tension, tip shape etc.) cause the resin to creep towards the probe tip. The resin is likely bulging towards the bottom of frame because this was the last part of the probe to leave the resin's surface when dipped.

Probe 9 was refitted to the μRepRap, touched off on a glass slide coated with Vivid marker, and then repeatedly touched off at 40μm intervals. The intervening height was 20μm to avoid probe or fluid drag. The slide was then micrographed at the same magnification as Probe 9:

(Note: There is some spherical distortion in the images due to impromptu photography setup.)

The first few dots (left) are a little larger than the others. The rest seem a relatively consistent size. The experiment was terminated after approx 60 dots (some are out of view) due to time constraints, and resin was still being deposited.

The dot size is clearly less than 40μm, though due to the optics and imaging used the exact dimensions are not apparent. It would appear to be in the order of approximately 20μm. This is adequate, and Probe 9 will be used for layer experiments.

Unfortunately, I'm going to have to leave you with a bit of a cliff-hanger because I have to do more hospital things for a few days. I fully expect to return. Might write a few more things up while I'm gone.