This is the third part of a series of projects intended for first year calculus students. In this series, students will learn how to use different mathematical equations to assess the properties of solids and containers.
In this part, we will be using our molds we created in part two to create permanent castes to use later on in the project. To do this we will learn how to make our very own, cheap, silicone casting substrate.
I optimized this thing to be printed in ABS with maximum settings. I would recommend a skirt with an offset of 0mm (otherwise known as a brim) with 2-5 loops for ABS. As can be seen from the photo, an increased infill may be helpful as well.
For this project I used a free program from Autodesk called TinkerCAD. I have long been a user of AutoCAD which is a desktop drafting program from the same company. I used TinkerCAD to make it easier for educators and learners to be able to more easily replicate what I did. TinkerCAD is awesome because it's not only free, but it's easy to use. It also runs in your browser and has built in instructional lessons.
For part 3 of this project I started out with our product from the part 2. If you remember, we used X=20mm which gave us a base of 60x20mm, two flaps with dimensions of 60x20mm, and two flaps with dimensions of 20x20mm. We then made this into a mold by adding a channel around the base and extending the flaps.
At the end of this part of the project, students will have a permanent mold of the volume that they will be using equations to find. Not only will this be a visual aid, but will help them to check the accuracy of what they are doing.
Even though the overall project is designed for Calculus students, this part of the project can be used for algebra or even art students as well.
Teachers will need to get all supplies ahead of time:
100% Silicone caulking
Caulking is available in all types and brands, but what you need is simply 100% Silicone caulking. Any brand will do, so buy whatever is on sale. The white kind is better than clear, as it's easier to tell when it's thoroughly mixed. This forms the bulk of your mold. Get a caulking gun too, if you don't have one already.
Plastic Cups, Silverware, and Straws
The silicone won't stick to the cup after it's cured, and you can throw it away when you're done. The straws are helpful if you don't have any pipettes or eyedroppers.
- Corn Starch
The cornstarch is essential to this. It will absorb the moisture in the mix and allow it to dry throughout.
Step 1: Add ingredients
Your ratio determines how long your cure time is. A ration of 1:1 should give you about 5-10 minutes cure time. This should be about right for this project. You will want your mixture to be about the consistency of cake frosting when it is all mixed together.
Step 2: Mix
It is important that you mix it thoroughly. If you don't then the caste will not dry evenly and in extreme cases cold cause it to crack.
Step 3: Pour
Use what ever item (silverware, pipettes, etc...) you have to spoon/pour your material out with. Make sure it is even with the top of the mold. You can use a flat object (such as the back of a knife) to run along the top of the mold and wick away the excess.
Step 4: Let dry
Parts this small should be dry in 1-2 hours.
This caste was made using kinetic sand
The students will now have a cheap, hands on way of making a caste of the volume they will be using equations to find, This will give them a visual and tactile way of understanding what they are doing. This will also give them a way to check their work, shown in the next part of this project.