Moldmaking Pour Gates and Piece Molds

I would love to see others' examples also; for now I just wanted to make sure I could watch this thread closely from the beginning.

I like my pour gates best on ball ends, because they are very easy to sand off, and also because you dont have to rely on pressure to fill your cup-shaped socket ends.

I know some people make seperate balls, not building them into any part of the arm though, for ease of casting... though I am not really certain how this makes things any easier. *L*

A nice flush socket, perfectly molded to fit the ball, would require a third part to the mold, yes. May as well make a third part to the limb molds anyway, if you're going to the trouble of making a three-part for all the torso and head peices. But you may want to just sand things to perfect instead of striving to get a flawless cast over and over. Depends, I guess, on how many casts you intend to throw, and how much finicky work you want to do to each cast.

The BEST photos, by the way, of casting process for bjd making are on BishonenHouse's website. Though he doesnt nitpick much about the joints...hmm... maybe we should bug him to. :LOL:

 

Minicurious, have you posted any WIP pix of the project you're molding? I'd love to see what you're up to!!

Sorry, I haven't got any pictures, but I will take pictures when I start making new molds in the next couple of weeks. I'll see if I can get a few shots of my old molds and I may have some junk pieces that haven't been cleaned.

In the meantime; I like to put the pour gate (and air vent) at the ball-end where possible. Some of my parts have sockets at both ends, in which case I put the vents at the sturdiest end that will be least affected by movements in the still-soft resin if I demold a little early. It's easier to take the vents off the ball cleanly, harder to get inside the socket to remove the sprues afterwards, so if I need to do it on the socket end, I place the vents on the outside of the part.

As for molds, all my molds are one-piece or split block molds with cores. This means only one seam to sand on each piece, but it's harder to get inside the mold to apply mold release etc. Basically all the gates and vents are attached, and will stick out above the level of the poured silicone (this is where translucent silicone is really handy). When you're ready to demold the master-part, cut into the mold (ideally using a mold-key knife, so the sides will go together again neatly) and take the piece out.

For the torso and head parts I have two-part molds in that there is the split-block outer and an inner piece that is poured in a separate sitting.. these pieces key together inside the mother-mold which is a hard two-part casing made of magic sculpt.. I also play to use some PVC pipe next time around. For the limbs I use split block outer molds that have internal keys for silicone "rods" (which are kept rigid by knitting-needle cores, or cores of bamboo skewers.. these are removable to make it easier to get the core rods out), and means I don't have to drill anything.

I don't think it's necessary to have a separate mold-section for the socket.. remember the seams between the molds don't have to be straight lines so you can build the socket into one half of the mold, and the ball-end into the other/second pouring if you're doing a two part mold. Using a third piece just makes it harder because that piece needs to line up with the other two, and it's another spot the mold might leak. Unless the socket is very deep, you shouldn't need a third piece.

Kaye taught me how to mold and she was honestly the one who figured out where to put the sprues on my parts the first time around. You need to put them at the highest point so no air is trapped (although using a pressurepot helps, air can still get trapped) and where they won't be in the way too much and won't be a detriment to the sculpt.

For the twigLimbs parts the lower legs, lower arms and upper torso are cast upside down, while the upper legs, hips, upper arms and lower torso are cast the right way round. The knees, elbows, ankles, wrists, hands and feet are all small one part molds that have been cut open to get the pieces out.. the mold-boxes hold the silicone together so they don't leak when casting.

 

You can get the mold-key knife from Barnes Online... (scroll down) they call it a jelly knife on their site. For US moldmakers you can also get it from Polytek.com where they do call it a mold key knife.

I have mold-release in a spray can, but I don't use it in the split molds since I can't be sure it distributes evenly. I use a sprinkling of talcum powder instead.

Your daughters scoobies sound like a functional idea ~ are you putting them inside the molds or planning to cast them inside the resin and pull them out. Not sure if it would stick or not.. I guess you will find out

Also seamlines should be neat, they just don't have to be straight but can follow the natural lines and curves of the body parts.

Lastly, I think you are probably more talented than you realise and you should have a go at making a head for your doll, too!!

 

Have you checked this link?
http://www.danperezstudios.com/workshoppages/molding_casting.htm

I looove this tutorial and I recommend it whenever I can. It give some really great, refreshing ways to consider seamlines - I always get trapped into thinking that they need to be straight... when really, they can be very creative to help you demold and avoid bubbles.

 

Also check out all the really cool video tutorials for moldmaking on youtube.com... search for "smoothoninc" and "brickintheyard".

 

I use platsil (addition cure) which is more expensive than tinsil (condensation cure) because it is better and lasts longer. I would check armsmodelit.com.au, solidsolutions.com.au and rowetrading.com.au

I use shore A20.. and I just bought some A40 for two piece molds but haven't used it yet.