Ear Posts

Resin Ear Posts
Wood Forms Wood Master Mold Box
Wood Forms Wood Master Mold Box
   To make the master ear post, I started with a couple of basic wooden shapes from the craft store: a 1.25" ball, a pencil pot and a 1" dowel. I turned down the dowel on the drill press (no lathe, yet) to make the stem, drilled a hole in the ball and glued the stem. I then sliced off the end of the pencil pot and turned it down, and glued it to the top of the ball. Some wood putty to fill in the gaps, round off the base to fit the radar section, a smaller dowel on the base, sand it smooth and apply about 4 coats of spray shellac. The dimensions match Dave Painter's plans except where the post goes into the radar section, which I made .625" instead of .600" for a better fit. Next is the mold box, made of Legos, of course. At this point, I sprayed a couple light coats of mold release on the inside of the box.
Clay Bed Embedded Master Top Poured
Clay Bed Embedded Master Top Poured
   Next, I laid down a bed of plasticine clay, then sprayed the master with mold release, pushed it into the clay and built up to the midway point with more clay. The holes are to align the two mold halves. Next, I mixed up a batch of of Por-A-Mold, from Synair. Por-A-Mold is a 2-part polyurethane mold making material, which gels in about 35 minutes, and cures in 24 hours at room temperature. The two parts are mixed 1:1 by volume, so no scales are necessary. I used the medium variety. I had a little trouble with the first pour, in that some unmixed curative stuck to the bottom of the mixing cup and ended up in the pour. It never cured properly, so I threw it out and mixed up another batch. My shop is on the cool side, so this time I made sure the materials were warmed up before mixing, and took it upstairs to cure.
Clay Removed Scroll Saw Master Removed
Clay Removed Scroll Saw Master Removed
   After letting the top cure for 24 hours, I removed the clay, and cleaned off the top of the master. Mold release on the master, mold half and the inside of the box, then another batch of Por-A-Mold. After pouring the mix into the mold box, I took a tip from another hobbyist and set the box on my scroll saw table and turned it on, to help vibrate any bubbles up to the top. It seems to have worked, since there were no bubbles present when I peeled the mold apart. Note - Legos make a quick mold box, but they're a pain in the butt to clean up, since the polyurethane gets in the cracks.

Last updated on Monday, July 28, 2014