Tuesday, October 18, 2011

Arisu's Head Cast in Resin

From a previous post I determined how much resin to mix.

I ended up mixing a bit more.  Since A was close to the 1 Tablespoon mark, I decided to make mix 1 Tablespoon of A and B.
1 Tablespoon A = 14.7g
1 Tablespoon B = 13.3g
Total A+B = 28g

If 1 Tablespoon = 0.5 fl.oz, then I mixed a total of 1 fl.oz of resin (A+B).  That means 1 fl.oz of resin weighs 28g.

This is the first urethane resin cast I pulled from the silicone mold.  The resin used was Smooth-Cast 300.  I used a syringe (without needles) to put resin into the molds until I see resin coming out of the vents.  I should try without the syringe to see if it reduces or increased bubbles.

Although the face itself is bubble free, it seems bubbles did get trapped in certain areas.  I also screwed up the magnet polarity.  That means the 2 parts don't want to stay closed.  I removed the gates and vents and did a little cleaning before the picture you see above.

I cast one more time with the correct magnet polarity, but I was impatient in trying to remove the face plate from the silicone mold so the ear part of the silicone mold ripped.  It was very tricky so it won't be a big deal that I will have to correct future casts in that area.  I also snapped the tab on the head cast.  You can see below that piece is on the bottom right.

The casts look good on the outside.  But require some cleaning and work to make them match up properly.  At least my second cast has a proper magnet polarity.

Its when you look on the edges do you see where the rather large bubbles are.  I can hardly find tiny bubbles.  If you will notice that the bubbles are located in nearly the same places for both casts.  So some changes will need to be made to the mold to ensure the bubbles are escaping properly.

Otherwise these casts came out rather well considering.  I plan to see if I can get a better cast without the bubbles another day.  I plan to clean up and make the cast ready for use in making a production mold.  I don't have to worry about making this mold until after I get a pressure pot and air compressor.

The first cast weighed 18.8g (both head and face plates).  The second cast weighed 18.5g.  It will probably be a little more when the bubbles are all gone.

I previously estimated I needed 19g of resin to cast both parts, but it seems that is just about enough for the heads themselves and doesn't leave enough for gates and vents.  So it is a good thing I mixed more than I needed, but it is a good idea to still lessen the amount of waste produced.

If I mix 3/4 fl.oz of resin (A+B) and 1 fl.oz of resin is 28g, then I need 21g of resin.
Weight of 3/4 fl.oz of resin = (28 / 4) * 3 = 21g

So in the future I will mix 11g of A and 10g of B by weight.  Or 3/8 fl.oz (3 drams) of each A and B by volume.
A = 21 / 190 * 100 = 11.05g
B = 21 / 190 * 90 = 9.95g

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