Why Lego mold boxes are cool

This is going to be another long post, but this is where using the Lego mold box gets fun. In the last part, I had my marble (well, bead) keys made. In this picture I've added another layer of Legos and poured a thin layer plaster over the rubber. The plaster will serve as extra support for the final mold, making it even less likely that the design will distort. The keys I created on the back of the rubber will hold this plaster piece in place. (The molds in this post have plaster supports top and bottom.)



Here I've taken off that extra layer of Legos to expose part of the plaster support. I don't want to expose it all, since the mold box is going to help hold the plaster in place for the next step. Notice that I took the mold off the green laminate board after my rubber set up.



That's because from this point forward, I'm going to be flipping the Lego box over a lot.



Here I have the upside-down mold box with the plaster support partially exposed. This will let me sand the plaster support level and round the edges and corners to prevent chipping.



Here's my leveled plaster support. I've also replaced the layer of Legos I took off before, so everything is the same as it was at the start of this post. (Except that my mold will now sit flat on the table when it is finished.)

Now I'm going to flip the mold box upside-down again.



Sometimes I can grab a bit of clay and all the clay will pull free. It didn't work so easily this time, probably because the foal is textured, so I remove layers of Legos until I can see the area where the clay meets the rubber.



Here I am lifting the clay from the rubber piece I poured yesterday.

This is where the Legos come in. The second side piece will pour against this first piece. The normal procedure would be to unbox the first mold piece along with its plaster support, and then rebox them for the second pour. But Legos can be added to what was the bottom - now the top - of this mold. They just have to be built upside-down! But there is no re-boxing, so everything remains sealed.

This is time saving, of course, but it's particularly helpful with really small pieces. The less the rubber gets disturbed, the greater the chance the original remains sealed in place. If the seal hasn't been broken then excess rubber cannot seep between the original and the first mold piece, which means one avenue for distortion has been closed off.



I've removed most of the clay in this picture. I haven't bothered to dig out the area between the legs - in fact I placed those pieces in sections so they would remain after the perimeter clay was pulled off. I'm going to have to clay those areas during the next step anyway.





I've started to clay in my inner pieces, which get poured last. I've started to build my Lego wall where I have the clay, but I've left most of the wall off for now so it's easier for me to work. When the inner mold pieces are clayed up, I'll add the rest of the wall and pour the rubber.

That flexibility is why I find the Legos so useful. I can build my mold box in either direction, depending on what piece I need to make. I can also put part of the mold wall in place if it's helpful, or take part down, depending on what I need to do at the moment.