Help needed with silicone mold making process

Sorry for having to ask these questions here, but I can't seem to get help anywhere else, and tried looking for specific forums dealing with molds to no avail. I ordered a "starter kit" From Smooth-on.com and am trying to plan out everything before it arrives so that I can make my first molding experience a pleasant and smooth one however, I have thought of a few problems that I am going to run into and am in need of a little expertise in this area. While my molds will not be very large, I am going to put a lot of small parts inside to be casted later on. Upwards of 36 in a 6"W X 4"L X 5/8"H block. I have laid the parts out and they should have sufficient space between them, especially if they will stay put during the pouring process.

First, What can I use to hold all of those small parts in place while the mold is being poured and setting up? I was thinking of something like a spot/strip of silly putty or maybe a slice/strip of double sided tape? I m unsure of how the silicone would react to that stuff though? As for setting up the parameter of the molding box I had planned to use simple scraps of MDF/plywood lined with tinfoil. Again I do not know how the tinfoil would react with the silicone and will the mold release easily once it is set? Lastly, How deep does the mold really need to be if the tallest part I am making a copy of is only like 5/8" tall? Would simply going approximately 1/8" - 1/4" deeper be sufficient? THX for your time and help.

1. I have used small pieces of Scotch double-sided tape with great success. It does not react with silicone but beware that any exposed surface of the tape will eventually stick to the hardened mold. If you are using softer silicone, it may be more difficult to separate the tape and mold.

I prefer to use tiny drop of instant glue to anchor small parts but you need to be smart to know where to glue the parts as you need to clean the glue later.

Make sure all the parts stay attached to the base before you pour silicone otherwise silicone is dense enough to lift/detach them, small parts in particular. Also, once silicone is poured and before it hardens, I tap at the bottom of the molding setup to dislodge any trapped bubble.

2. Any smooth surface will not stick to silicone. Tinfoiled plywood is fine but plywood is not. I use styrene sheet.

3. 1/4" deep should be fine but how thick the mold needs to be really depends on how flexible and soft the silicone mold is. You need to make sure the mold is not too thin as later on when you cast, you want some flexibility and strength in the mold so that you can stretch it as you separate casted parts.

Hope this helps. Good luck!

Thank you VERY much for the help. I think I got most of it now with those few small detail problems out of the way. I never thought of using a glue to attach the parts haha, and if I were to use the sheet stock as the base with tinfoil lined sides it should be pretty easy to assemble/break down and keep the costs to a minimum. Again, Thanks a lot for the help!! I should be casting in a few days time now!! :)

You better look on Youtube. It have many sample that show you how to make it.

2 kasha: Have you already thought about casting process? Notice, that each part inside closed mold should have two outs: one for resin pured in and one for an air going out, or else you will get air bubbles in your casting. I use plastic sprue pieces, glued to part as billets for intake/outlet ports.
If I was you, I would stick parts by those intake/outlet billets into plasticine base and surrounding the base with styrene walls. If your molds will be opened, you can just stick parts in to plasticine by the side not to copy. When the mold cures, just turn it upside down.
Usually minimal thickness of the mould walls is aproximatelly 10mm. It depends on the size of the part to copy. As you will copy small parts, I guess 1/4" would be enough.
Think over the position of each part. Its location shoud let the air go out freely, not stucking in corners.
I hope this helps.
Good luck!

Hi,
I have a small experience in molding and casting but I can share what I've learned over the time. I tend to make many smaller moulds then one big because if something happens you will only lose a mould for few elements plus it is easier to get cast out.
When I make moulds I make a small box out of cardboard and I glue in elements using white glue (for paper etc.).
I don't usually make hole for air to go out because I'm using a small pressure chamber but if you won't be using one of those it is important to place an element in such way that will allow air to go out when you will purring the resin in.
Some time ago I maid SBS on mould making and casting in one part mould if you are interested and there are no objections I can post it here.
As for 2 part moulds I'm planning on making couple of those in near future so if there will be an interest I can also make an SBS of that.
Regards
Lukasz

First, What can I use to hold all of those small parts in place while the mold is being poured and setting up?

Kleen Klay or Klean Klay.

http://www.kitkraft.biz/product.php?productid=1987

Build your box with Legos. Cast on a piece of glass.

hth,
Bill

With the product I am using for the silicone (OOMOO 30) the use of a degassing chamber is not really needed. I think that the majority of the air bubbles that are shown in the videos are from the mixing process. From what I can see in the videos and pictures the mold looks pretty solid minus a few small bubbles none of which are in the final details.

I think I am set on using sheet styrene for the base so that I can use a drop of instant glue to attach the small parts and keep them in place. Simply lining the MDF walls with some tinfoil should help seal the small 5 corner box together. I do not have any LEGO's and am not about to spend that much to build up walls when I can do it from scraps in the wood shop and 1/8 roll of tinfoil, maybe some dollar store masking tape too hehe.

As far as the casting process goes I haven't put much thought into that as the process I am going to use doesn't really require it. I just have to mix the resin up, pour into the cavities, and level off with a piece of glass as shown in this process here. http://www.hirstarts.com/casting/plastic.html
Also by going that route I don't have to fill all the cavities at once so that if I need a few more of these or those the whole thing doesn't have to be filled, just the ones I need.

I should be able to get started this weekend on this whole adventure thanks to everyone's help.

With the product I am using for the silicone (OOMOO 30) the use of a degassing chamber is not really needed. I think that the majority of the air bubbles that are shown in the videos are from the mixing process. From what I can see in the videos and pictures the mold looks pretty solid minus a few small bubbles none of which are in the final details.

I think I am set on using sheet styrene for the base so that I can use a drop of instant glue to attach the small parts and keep them in place. Simply lining the MDF walls with some tinfoil should help seal the small 5 corner box together. I do not have any LEGO's and am not about to spend that much to build up walls when I can do it from scraps in the wood shop and 1/8 roll of tinfoil, maybe some dollar store masking tape too hehe.

As far as the casting process goes I haven't put much thought into that as the process I am going to use doesn't really require it. I just have to mix the resin up, pour into the cavities, and level off with a piece of glass as shown in this process here. http://www.hirstarts.com/casting/plastic.html
Also by going that route I don't have to fill all the cavities at once so that if I need a few more of these or those the whole thing doesn't have to be filled, just the ones I need.

I should be able to get started this weekend on this whole adventure thanks to everyone's help.

I use Smooth-On for my castings and OOMOO 30 will trap air bubbles. Mix slowly and pour from a long height to minimize trapping bubbles. Also you can brush on a layer over your patterns as well.

The great thing about using the Klay is that you can easily make 2-part molds and it will not stick to either the silicon or the resin.

Lego's rock. Find some at a garage sale. :evillol:

Anything will work and a craftsman never blames the tool. Create a process that works for you and perfect it!

More often than not I use double-sided tape method on one piece molds with the part slightly raised on a shim of plastic that is a little bit larger than the part being cast.

This allows for a smidge of over pouring and gives ya something to grasp onto while removing the piece from the mold after curing

Junk CD jewel cases kick butt for a base with a simple box made from four pieces of styrene. I keep it about a quarter of an inch away from the part being cast, but I prefer higher shore hardness

I think I'm addictive to Alumilite's UMR . . lol

It works awesome on both silicone and urethane molds.

http://cactuscarmodler.com/index.html

Go to this link, then click on the forum, then scroll down to bottom to the resin casting subject. This is how I do it. Start reading at the bottom entry first and work your way up. I make clear resin parts too.