{"data":{"model":{"id":"516343","slug":"bath-bombs-from-3d-prints","name":"Bath bombs from 3D prints","authorship":"remix","eduProject":{"id":"2109","subject":{"id":"48","name":"Practical prints","slug":"practical-prints","__typename":"SchoolSubjectType"},"language":{"id":"38","name":"English","__typename":"LanguageType"},"free":false,"timeDifficulty":"SHORT_TERM","audienceAge":"SCHOOL","complexity":"EASY","equipment":[],"suitablePrinters":[],"organisation":"University of Pennsylvania","authors":"Tex Kang, Program Coordinator of Technology and Play","targetGroupFocus":"

The focus of this project is too allow students to become familiar with TinkerCAD's functions and educate the idea of a positive volume and negative volume in space so we can create a viable mold.

The hands on activity also serves to as a fun activity that engages students to create by learning a bit of chemistry in bath bomb making and mixing different materials and addivitives they prefer into their personalized project.

","knowledgeAndSkills":"

Using TinkerCAD to change 3D file into a printable mold. Students should be able to sketch independently in TinkerCAD and will need to use several commands such as dimensioning, positioning, rotating, aligning, grouping (combining) and understand concepts of positive and negative volumes.

Mixing and packing bath bombs into the 3D printed mold. Students will need enough strength be able to pack the bath bomb into the molds (think wet sand on the beach) so that it can be compressed and hold together.

","objectives":"

Converting a 3D design into a negative volume and creating a 3D mold
Making a bath bomb and shaping it using a 3D printed mold

","equipmentDescription":"

3D printed molds

Mixing containers: depending on how many students you will have, you will need multiple large mixing containers. Buckets are not ideal as some students will not have long enough arms. Look for under the bed containers which are not too tall and usually have wide bed areas. Multiple containers are recommended in order to provide different mixtures of bath bomb ingredients.

Bath bomb ingredients, measured by weight:

Dry:

4 parts baking soda or sodium bicarbonate
2 parts citric acid
1 part cornflour (not necessary but acts as a binding agent so it helps)
1 part epsom salt (optional)
Food coloring powder (I recommend powder instead of liquid as some liquid ones react to the ingredients during mixing) (you need enough to get the color you want, a little (maybe 1/5th a part) does go a long way though) (optional)
Additives (anything dry is fine such as rosemary, lavender petals, dehydrated orange peels, green tea, etc.) (optional)

Wet:

2 parts oil (I used coconut oil but you can use other ones like coconut or olive, check for student allergies)
Essential oils (check for allergies again) (optional)

Gloves (one time use waterproof ones)

Mixing utensils

","timeSchedule":"

You will need two separate 1 hour sessions, one for using TinkerCAD and another to make the bath bombs with the 3D printed molds.

The TinkerCAD session will be easy to do as it requires you only teach how to use the negative volume feature, resizing the design to your specifications, centering/combining it to a slight larger positive volume, and exporting it as a .stl file. I think it will take 30 minutes to teach to 10+ year olds with experience in TinkerCAD and they can spend the rest of the hour designing their mold and then sending/saving to their instructor.

Depending on the size of the molds, number of students, and how many 3D printers you have it can take an hour to a few days to prepare the molds. If you do not have the time to do two different sessions, you can just 3D print some snowball makers (ex. https://www.printables.com/model/92262-snowball-maker) into an appropriate size and prepare them before hand so students will be able to make round bath bombs in one day.

The bath bomb making session will require about 30 minutes to measure out the ingredients, mix, and divide into different containers. You can also prepare this step prior to save time if you prepare the majority of the mixing and dividing into containers and only leave one container empty, which will be used to make a demonstrative (to show students what ingredients and what ratio they are mixed) batch. You should also prep the area in case there are any spillages or for easy clean up after. Students can take about 10 to 15 minutes pack their bath bomb mixture into the plastic molds, help some students with molds that have smaller details by pushing the mixture firmly into the mold. Ideally wait at least 15 minutes (also depends how humid/hot the environment is) before attempting removal. You can always let it dry overnight as well and have them pick it up another day.

","workflow":"

TinkerCAD will be used for this workshop as it has an easy to use Negative Volume feature and easy to use interface for younger students.

The design we will use can be either created by the student or downloaded on a 3D print database. Just make sure that when the design is created or selected, you do 2 things: do not have any overhangs, which will not allow the bath bomb to release from the solid mold easily and make a flat side to act as a the surface of the mold. To understand overhangs and design workarounds, please refer to this guide: https://blog.prusa3d.com/the-beginners-guide-to-mold-making-and-casting_31561/

To make a flat side, just create a large rectangle that is negative volume to \u2018cut\u2019 away from the design, creating a flat surface. This procedure will be explained with illustrations in a pdf included in the project files.

Once these two conditions are informed to students, continue helping them to turn their design into a negative volume of their design. Once they do, select a basic shape (usually a square, rectangle, or cylinder works best) from TinkerCAD that best fits the negative's shape. Make the basic shape larger (not too large, it will take more time and material to print otherwise) than that of the negative volume and align to the center of the two objects as well as align to the cut flat side of the negative design to the positive basic shape. Make sure the positive basic shape is indeed bigger than the negative design in all X, Y, & Z axis and no holes can be created. Combine them to create a mold of the original design. Adjust the mold to your needed size specifications and print out.

After all the molds have been printed, you can arrange another class for the bath bomb making session. The bath bomb making procedure can be simplified if you pre-mix all the required components to the right ratio. I have provided a recipe with the units in parts as I do not know how many students nor how big your bath bomb will be so you should test out making a bath bomb first and calculating how much more you will need. There are also other recipes online for DIY bath bombs so yo do not need to use mine and feel free to experiment. Once you do pre-mix just the required components (baking soda, citric acid, cornflour, oil) (also always mix dry ingredients with other dry ingredients first before introducing wet ingredients) check its consistency to make sure it can easily be packed into a shape and retains its shape. You can add the epsom salt at this point if you wish and mix it. Then divide the mixture into separate containers and wait for class, you may need to cover the mixtures if the class is a few hours away as it may dry out (if it does dry out, adding a bit of oil will give it back its pliable nature).

Once students do arrive, interact with them and ask/vote on what optional additives should be used for each container. This is an important step as some of the ingredients can cause allergies so make sure to ask students and also allow them to design their bath bombs with the different choices. Feel free to mix colors, add different herbs, try some smells that they can add. They can make the bath bomb from a single mixed container or they can mix and match from different containers, just make sure you the container contents are not too mixed in case one container contains allergic components to a specific student.

Apply some oil into the 3D printed mold to act as a release agent before adding in the bath bomb mixture. Pack the mixture into a 3D printed mold with enough force so it cannot take on any more and then cut off the excess. You can also choose to include a 3D print inside the bath bomb as a fun surprise as 3D prints are mostly hollow and will float once the bath bomb melts away. I made a pokeball shaped/colored bath bomb and added a squirtle inside it while packing for fun but feel free to add anything else as long as it fits in the bath bomb.

Let the mold with mixture dry a bit before attempting removal. Using a rubber mallet or firmly striking the plastic mold upside down while it is on a desk/paper sheet allow it to release a bit easier.

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Bath bombs from 3D prints

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