Mold making question, now casting Q

Sundowner

Master Member
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I'm in the process of making a silicone mold but the object is tricky. I'm trying to mold a badge and its curved. It seems like the silicone would just run underneath the voids so I'm thinking I may have to clay up the void spots. Does anyone else have an insight on this? Maybe something I'm missing? Thanks!
 
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Re: Mold making question

If it has a major curve claying would be your best option. You could also try to get some thin plastic and form it to the same curve as the badge so there's a plane that is the same curve as your badge to get rid of the void.
 
Re: Mold making question

If it has a major curve claying would be your best option. You could also try to get some thin plastic and form it to the same curve as the badge so there's a plane that is the same curve as your badge to get rid of the void.

It's a star styled badge so the curve is really aggressive. Thanks for the reply!
 
Re: Mold making question

Clay in the void with an undercut. It wont take much. You can also cast a pin assembly in while the material cures. Simply run the pin through a stir stick and set it atop the mould as the material is curing. Ive done this at least a thousand times on everything from badges to name tags to pilot wings in rubber, plastic, feather light... The plastic pins even have a couple holes pre marked to drill through for the material to bite into.

b84y1k.jpg
 
Re: Mold making question

Can you post a picture of what you are molding? That might help.

Sure can! I tried making a mold but it was too rough and uneven angles that it ran resin everywhere. I plan on giving it another shot. Here are a few pics
image.jpeg

Clay in the void with an undercut. It wont take much. You can also cast a pin assembly in while the material cures. Simply run the pin through a stir stick and set it atop the mould as the material is curing. Ive done this at least a thousand times on everything from badges to name tags to pilot wings in rubber, plastic, feather light... The plastic pins even have a couple holes pre marked to drill through for the material to bite into.

http://i67.tinypic.com/b84y1k.jpg

That is a great idea! I was just planning on gluing small badge pins to the back.
 
Re: Mold making question

Make triple sure to drill out a couple holes in the plastic for the material to bite into. Also I forgot to mention use a nail file to scuff the surface of the plastic on both sides. This will allow more bite for the material to grab and hold onto while worn.

For badges youll have to consider a stronger casting material or one that has flex. Standard cheap casting resin is brittle and were talking a part thats going to be thin with stress points being a star.
 
Re: Mold making question

I've been pretty happy with SmoothCast 300 -- it is a white plastic, casts quite well, roughly the strength and flex of styrene.
 
Re: Mold making question

Ok so the I took Robstyle's advice and filled the voids and made a mold. It turned out great! However new problem, I casted two badges and they were perfect but the third casting wouldn't cure. I cleaned everything up and put away the materials. Today I casted two badges that turned out great but the third wouldn't cure. I cleaned everything and tried again but it would not cure. I'm measuring everything even, good tempature indoors and mixing the resin for 90 seconds. Any ideas? Do I need to clean the mold before every casting?
 
Update, I shook A and B separately and poured equally into two different cups. I poured both into one cup and stirred for about a minute. I left the resin in the cup to see if it would cure and after 30 minutes it was still slimey. I'm getting pretty frustrated
 
Re: Mold making question

Do I need to clean the mold before every casting?

Not sure what is going on apart to say that maybe the batch of resin you have is either past its shelf life or has moisture contamination.

These 2 part plastics normally cure quite fast and leave the mold clean for the next batch.
 
So on the first day you were able to cast two badges, but the third never set up, and the same thing happened on the next day as well? What kind of resin, and what kind of cups are you using?
 
Not sure what is going on apart to say that maybe the batch of resin you have is either past its shelf life or has moisture contamination.

These 2 part plastics normally cure quite fast and leave the mold clean for the next batch.

I bought it brand new from Smooth-On

So on the first day you were able to cast two badges, but the third never set up, and the same thing happened on the next day as well? What kind of resin, and what kind of cups are you using?

Day 1: First 2 casting were perfect. The 3rd would not cure.
Day 2: First 2 castings were perfect. The 3rd would not cure and every attempt after that was worse than the previous.

I'm using Smooth Cast 300 and I'm using small plastic cups like this

translucent-plastic-cup.jpg
 
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I had that happen once, I figured it was from the material sitting. I shook it up really hard in the container in the morning and then used it in late afternoon to let it settle and it was fine.
 
Thanks for the replies. Smooth On said do not stir A&B for more than 90 seconds but reading through some old posts, i read that maybe I should stir longer. Bingo! I stirred for 2.5 minutes and they are curing perfectly. Again thanks for taking time to help me solve this issue!
 
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