Molding and Casting Kit Parts for the Y-Wing Project

@DaveG just to say thanks for your clear instructions and guidance , I have cast my first parts which means I can continue my studio scale journey
first mistakes I made so others can avoid

I didn't leave enough room around the edge to allow the glue gun in to seal the edges to the wall, so I glued underneath , this meant the mould box was slightly unlevel , meaning when the silicon dried and you go to pour in resin in flows away from what your filling,
SO LEAVE SPACE AROUND YOUR PARTS, AND POUR YOUR SILICONE ONLY WHEN YOUR PARTS ARE ON A LEVEL SURFACE

Believe the curing time on your resin contains , it is ACCURATE .
When I poured my first batch of resin , I didn't believe I had mixed it correctly as I couldn't feel too much heat initially
first two moulds were going fine , third moulds disaster ......as I'm pouring its turning white as it's hitting the mould , and I watch in fascinating horror as it hardens as I pour all the way to the jug (see exhibit A) great fun but a missed parts opportunity, but a learning experience for not only me , but my family as I ran downstairs with a lump of red hot plastic to demonstrate exothermic reaction (yes there was quizzical looks )

other miss is was not putting a flat surface with weights on top of the resin, this let to a waste of resin , and rounded rear of parts that need sanding

one step I personally would remove is using rice to measure the volume , do it with maths as the clean up of rice from the mould was a pain

you will see in the images the moulds are different colours , I think the second batch is more red , not sure but I think I added too much hardener , I may order Smooth-on with 50/50 mix for convenience. This was Polycraft general Purpose RTV

First Moulds
View attachment 683420

first castings
View attachment 683419
EXHIBIT A
View attachment 683418

Another schoolboy error, in my first castings I ran an old brush around the mould when I put the first resin in then continued the pour , this helped disturb bubbles.
On the second pour I forgot to do this and as a result there are more bubbles ,

for or the second pour I added a pigment to my resin .
this really adds something to the pieces once cast, there is a nice sheen off them, making them look like injected moulded pieces.

My favourite pieces compared to originals , even with some missing pieces they look great

Cockpit dashboard came out perfect as bubbles had room to escape via shield
other parts like Messerschmidt landing gear I couldn't cast correctly and even with air channels had errors so I have to revisit them

final advice , I think going forward I will mould my parts by the height of the piece this way I won't feel like I am wasting silicone.
mixing heights means your mould is dictated by the tallest piece , by placing all flat items together you will save a good bit of rubber .

Great experiences, thanks for sharing! I'd definitely look into getting a pressure pot for casting kit parts. It'll get rid of all of the bubbles. This works even when using a silicone backing plate to get smooth backed castings. Are you using a scale to measure/mix your silicone? Personally I'm not a big fan of Smooth-On's "mix by volume" silicone products. If you find getting the rice unstock from the tape in the mold box an issue try dusting the tape with baby powder first.

Keep casting!

DaveG said:

Great experiences, thanks for sharing! I'd definitely look into getting a pressure pot for casting kit parts. It'll get rid of all of the bubbles. This works even when using a silicone backing plate to get smooth backed castings. Are you using a scale to measure/mix your silicone? Personally I'm not a big fan of Smooth-On's "mix by volume" silicone products. If you find getting the rice unstock from the tape in the mold box an issue try dusting the tape with baby powder first.

Keep casting!

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Thanks Dave , I didn't weigh it I used the nearest 10% marking as a guide,
have you had issues with the mix by volume ? Or is it because it cannot handle fine detail?
And you supply another great tip , talc on the tape , thanks again.

im eager to build my next mould as soon as I restock

Generally mixing by volume is less accurate than mixing by weight, especially with viscous materials. Products that are mixed by volume were great back in the "old days" if you didn't want to spend money on an expensive gram balance scale but these days you can pick up a perfectly good digital kitchen scale for $15, so there's really no reason not to weigh the materials, both for molding and casting.

If you're finding the resin is kicking off before you can get it mixed and poured you can find resins that have a longer pot life. Actually my current favorite resin is Smooth Cast 300 (not the 300Q). It's got a long enough work time to mix and pour but sets up much faster than the SilCast II I was using before. I can de-mold most parts in 15 minutes with SmoothCast instead of the hour it took with the SilCast.

DaveG said:

Generally mixing by volume is less accurate than mixing by weight, especially with viscous materials. Products that are mixed by volume were great back in the "old days" if you didn't want to spend money on an expensive gram balance scale but these days you can pick up a perfectly good digital kitchen scale for $15, so there's really no reason not to weigh the materials, both for molding and casting.

If you're finding the resin is kicking off before you can get it mixed and poured you can find resins that have a longer pot life. Actually my current favorite resin is Smooth Cast 300 (not the 300Q). It's got a long enough work time to mix and pour but sets up much faster than the SilCast II I was using before. I can de-mold most parts in 15 minutes with SmoothCast instead of the hour it took with the SilCast.

Click to expand...

I was unfortunate enough to receive some 300Q on a order screw up. That stuff sets FAST, like barely enough time to mix fast.

Thank you for a great tutorial DaveG, I have a question.

The instructions state to cement the styrene sheets to the base, but do not specify whether or not to glue them to each other at the vertical seems, is that necessary?

Yes! Sorry, I should have been more specific. The vertical seems should also be glued with solvent cement to prevent the silicone from leaking out. I have updated the instructions.

Thank you, DavidG! I want to learn how to cast parts for future builds and after watching countless videos on YouTube it finally occurred to check the RPF. This was exactly what I was looking for!