Saturday, October 15, 2011

First Rotocast & Dead Spindle

I managed to get my first successful rotocast of silicone rubber in a plaster mold.  I applied 9% silicone thinner to the liquid silicone and two drops of accelerator before pouring it into the two-part plaster mod.  It took about an hour if slowly rolling it around in all directions until the silicone was cured enough to leave it alone.  I should probably use a little more accelerator next time.  Silicone was mixed 90A:9B (measured in grams).  It came out of the mold looking like a child's toy rubber ball, even full of air.  Still, there is a blob of silicone on one side that didn't get evenly distributed.  I suspect that it was the result of the mold sitting on the table while it fully cured out.  More accelerator and a real rotocasting machine should take care of this. 

This evening, I also was successful in milling out the bottom PCB cap for version 4 of the ball support.  Unfortunately, the motor on my spindle failed, so I won't be able to mill the other half of this support until the new motor arrives.  I also bought two more spares for next time.  They are only about $18 on Amazon.  The motor started to fail about half way through the job by running much slower and losing about half its power.  I slowed the job down to about 30% to take it easy and try to finish out the job.  I managed to get down to about two minutes left on the finishing pass (after 1.5 hours) and the spindle came to a full stand-still.  I was able to manually finish the part with some sanding luckily, so all was not lost.

Picture below includes the rotocast silicone ball for the hand support, the version 4 ball support cap that covers the PCB and the latest PCB that hasn't been populated with parts yet (shown inside the newly milled cover). 

No comments:

Post a Comment