RepRap Masterclass | Part One
15th of September, 2009
• introduction to the fablab concept
o powerpoint presentation
• introduction to the reprap darwin 1.0
o prototype review
• introduction to protospace
o guided tour
• step one | urethane casting of the structural joints and bones
we’re using the casting molds that were created during the previous reprap masterclass. these are available for public use at Protospace Utrecht. if you want to create these negative molds yourself, you’ll have to apply the process I’m about to describe by using printed models of the necessary parts, and replacing the urethane ingredients with a silicone liquid.
o preheat the oven to a steady 150C
♣ this is based on the specific casting material we applied:
♣ part A: water clear casting plastic
♣ part B: rigid urethane casting resin
♣ brand: crystal clear
♣ available at: formX, Amsterdam
o grease the silicone casting molds with Vaseline
♣ try to apply a smooth layer, since the grease won’t melt in the oven and therefore it’ll leave marks on your parts.
o heat up the greased casting molds to 150C
♣ safety first
o meanwhile, start mixing the casting materials
♣ in our case: part A - 100%, part B - 75%
♣ try not to overdo it volume-wise, the parts are relatively small and even at room temperature the urethane will start
to solidify from the moment you start stirring.
♣ when you’re stirring the liquid will first gain some color, but it eventually clears up when it’s mixed properly.
o remove the encapsulated air bubbles by using a vacuum pan
♣ don’t position your head over the machine while it’s in operation, because the cover might implode and the pieces
will bounce back in your face.
♣ the process takes about a minute, if the liquid starts cooking it’s because the boiling temperature of any liquid is
significantly lower in a vacuum environment.
♣ when the bubbles are out, gently release the vacuum and take out the liquid.
o take some heated molds out of the oven and start pouring in the liquid
♣ regarding the double-sided molds you need to make sure that the holes for material input and air output are
extended by cone-folded paper. this way they don’t get cluttered as easily.
♣ make sure the filled molds are placed on an even surface, let them cool down for about 15 minutes.
♣ gently remove the cast parts from the silicone molds. when they’re still slightly flexible you can flatten them some
more by pressing the parts onto a flat surface.
o apply some new grease to the emptied molds and place them back into the oven, repeat the whole process until all
necessary parts are created.
♣ it’s recommended to closely keep track of the necessary numbers and produced numbers to avoid overproduction.
♣ the results of this first day were sizable, about twenty parts created.
