How to Make a Plaster of Paris Clock at Home With a Silicon Mold

Bismillah

Hi! In this Instructable I will show how to make a clock at home from resin or cement or plaster of paris, using a silicon mold. The clock will be made by casting Plaster of Paris into the silicon mold. You can also use either cement, fiberglass resin or epoxy resin. I will show how to make the master mold in wood with a 3D router. Secondly you will make the silicon mold, and finally pour Plaster of Paris into the mold to make the clock.

• A 3D Router
• A piece of MDF of any other solid wood, not chipboard
• Sandpaper
• Spray-paint
• Ramwax or any other release agent
• A 2-part silicon rubber to make the mold
• Playdough or something similar
• Plaster of Paris
• A container to mix the silicon rubber and one to mix the Plaster of Paris
• Mixing spoon or stick
• Kitchen scale

The first step is to make the master mold using a 3D router. I designed it on a program called Easel. I used a 90 degree carving bit to carve the clock design. The depth is 4mm, which is the preferred depth. I then cut the outside edge with a straight bit 10mm deep. This will help to make the mold which will become evident in the next step.

I used MDF to carve the design, but the problem with MDF is the 'strings' that are left after carving. I normally spray a layer of paint on the carving and then sand it down to remove the strings (imperfections) and to have a perfect master mold to cast the rubber. I then use ramwax (a wax release agent available in South Africa) to coat the master mold so that the silicon rubber does not stick to the wood when I pour it over the master mold. There are probably many types of release agents available. You could even use vaseline, but I am not sure how smooth the mold will be.

The next step is to add playdough around the edges to prevent the silicon rubber from flowing away when poured. I didnt get a picture of it when I put the playdough. The silicon rubber is then mixed properly as per the manufacturer recommendation and poured. I buy my silicon rubber from my local fiberglass supplier. It has a shore hardness of 30 which is perfect for demolding. I usually wait a day before removing the mold.

The next step is to use Plaster of Paris to make the clock. The ratio is normally 1 part water to 2 Parts plaster of Paris. Remember to add the plaster to the water and not the other way around. You could add tempera powder to color the Plaster of Paris or you could paint the clock afterwards. Another option is to add the tempera powder just before pouring to give a marble effect.

You can also try cement, epoxy resin and fibreglass resin to make the clock. Plaster of Paris is what I currently have and it is probably the cheapest.

Depending on the finish you want you could leave the clock unpainted, color parts of it in with a marking pen or paint the whole clock. With the gold clock I spray painted it and then colored the black parts in with a marking pen.

With the blue one I added some blue tempera powder in before casting to give a marble effect and I then colored in the letters with a blue color pen (sharpie)

The final step is to add a mechanism. I had drilled a hole into the wood before making the silicon mold so that I don't have to drill into the Plaster of Paris. I drilled a 10mm hole, but you will have to drill the hole size depending on the mechanism you purchase. You can also take a mechanism from an old clock