Beginner needs help getting started!

Dear S23 GFI,

Hello. I have a project that I want to cast, and I need some help to get started.

The project is a clear plastic horn button for an old car. The PDF shows four pictures: the original button, the original prepared as a casting pattern in an outside (convex) view, an edge view, and an inside (concave) view. The button is supposed to be clear and has a domed shape. On the inside, there is some molded-in detail that needs to be reproduced. You can see from the photo that this 52 year old part has internal stress cracks. I am hoping to be able to cast a clear, bubble-free replacement that I can then paint to reproduce the original.

So I have many questions:
- Would I use a two piece mold?
A: Yes this would be a two piece mold.

- How much space should there b between the edge of the part and the edge of the mold? 1/4"? 1/2"?
A: 1/8-1/4" is plenty, silicone is to expensive to waste.

- If a two piece mold, which side do I mold first - the convex side (without detail) or the concave side (with the detail)?
- What mold material would I use?
A: The convex side, please look on the website there is a great tutorial under applications/automotive on doing tail light lenses. If you have degassing equipment, best to use the Plat 55 for the mold making material. The tutorial shows on tail light lenses, if you don't have equipment the best attempt at doing it with the least amount of bubbles. Without degassing odds are you will have some bubbles.

- I assume I would need some kind of mold release agent. What would I use to keep the tow mold halves from sticking together? What do I use as a mold release between the pattern and the mold? In the mold prior to casting the part?
A: Yes you will! Silicone wants to and will bond to itself. We have a liquid rubber to rubber mold release if using the High Strength silicone, if using the Plat series the UMR works well. Good old vaseline/petroleum jelly makes a good release too.

- How do I assure that I get the detail from the concave side into the mold?
A: The silicone will pick up both sides, with the two piece mold. You will have a male and female piece of the mold, creating a squish mold. (see tutorial on site)

- What kind of casting resin is appropriate for this project?
A: We have some who swear by the both, I would say for the lenses the water clear seems to be the one used most. The Water Clear is a bit more UV stable then the Alumilite Clear, but it is a little softer (it is still plenty hard and ridged) but the durometer is slightly lower.

- How do I get the casting resin into the mold? The two piece mold video shows opening the te mold at one edge, pouring the resin in, and squishing the mold closed. Will I be able to get a completely filled, bubble-free part by doing this? Will there be flash on the part due to leakage on the edge where I would pour the resin in?
- I have an old pressure cooker that I can use as a pressure pot. Would this help with the air bubbles? What pressure level would I use?
A: Look at the squish mold process not just the two piece mold, you will see how the squish mold works. Yes there may be some flash it can be removed with an exacto knife pretty easily. Doing the clay up process when making your two piece mold nice and even, straight can reduce your flash. You must have equipment if you are expecting no bubbles, the mold will have to be degassed in order to put the resin under pressure. You need to be able to achieve 50PSI. Safely achieve it, I don't know anyone who has used an old Pressure Cooker. A safe certified pressure pot or paint pot is the way to go.

I'm sure I will have more questions as the project goes on. First step is to make the mold.


Any suggestions or advise is welcome! Thanks in advance.

Remember silicone is NOT forgiving it will give you what you give it. It will pick up the cracks, perfections, imperfections, texture, finish etc. If you want a water clear piece you will have to prepare your original to give you such. Your original will have to be glossy/shiny to achieve that. If it is matte finish you will get a frosted beer mug clear, not water clear. I understand this is very old, please understand however slight the chance to take care of the original in this process.

S23 GFI along the way if there is anything else or we can help you please never hesitate to call there are plenty of people here ready to help you.

Have a great day!

Regards,

Carol