Rhythm Eggs (Egg Shakers) - 3D printed Percussion Instrument for Kids
My wife teaches Singing Time to children 18 months to 11 years old. She wanted to have something to give each child to help them learn rhythms. So we printed Rhythm Eggs, which are 3D printed hollow plastic eggs with rice inside. The eggs are very strong. To make them 'spill proof' the rice is added during the printing process so it is essentially sealed inside. The eggs are light, strong and have a good feel to them -- and make a nice 'chish' sound when you shake them. The kids love them. We printed over 40!
Step 1: Materials
Egg 3D File
1 Teaspoon Measure
3D Manipulation Software
Step 2: Manipulate 3D Egg File
Download a 3D .stl file for an egg. There is one on Thingiverse here that works nicely. Thank you Johan for uploading it!
The egg is very large so it needs to be reduced in size. It is oriented horizontally which is not ideal for 3D printing so it needs to be rotated. It is solid, so it also needs to be hollowed out.
I used Meshmixer free software to take care of these manipulations.
I went into Meshmixter to the left hand menu and selected Edit and then Transform in order to rotate the egg. You can rotate the egg so it is point-up or point-down. I found whatever end is on the build plate gets a flat spot. If the point is up the large end's curvature approaches the limit of unsupported 3D printing and may have some surface anomalies or issues printing. So you can decide on which orientation to print the egg in. I have printed in both point-up and point-down and each has merits. I kind of like the smooth point so I like to print point up.
The large egg needs to be brought down to a nice small size and I went into Meshmixer Analysis then Units/Dimensions which allow you to enter a specific numeric size. I made the egg 60mm tall, which approximates a real hen egg.
I almost forgot - The egg needs to be HOLLOW! So I went to the Meshmixter Edit menu and selected Hollow and adjusted the sliders to get a 2mm wall thickness. (Alternately you can print the solid egg, but have your slicing software print it with zero infill and control the number of layers that make up the wall thickness. I tired it both ways and I like hollowed out as it provides a more consistent wall thickness. It tends to get a bit 'weird' at the top and bottom when printing with zero fill and only wall thickness layers.)
I then sliced the .stl file with Cura free slicing software to get my final g-code. I have attached .stl files for a 60mm egg with a 2mm wall thickness in both point-up and point-down orientation so you can slice them.
Step 3: Print 3D Egg - and Pause to Add Rice
Print your Rhythm Egg.
I used PLA filament with 210 C nozzle and 70 C build plate. I have printed with as little as 20% infill and as much as 100%, both with good results. I actually think the 20% turned out better as it had hotend tool path that gave slightly better results.
I printed with a brim and supports on -- but only supports to the build plate - otherwise it may add supports inside the egg which you don't really want. Print time was estimated by Cura at about 2 hr 45 min, taking about 5 meters (15g) of 1.75 mm diameter filament.
You will need to pause the printing process to add rice into the egg. Depending on your slicing software and printer you may have good luck adding a pause command into your g-code directly or you may want to set a timer for yourself and check back about half way through the printing process.
When you get about half way you can pause the printer and add 2 teaspoons of rice (~5 g). Then un-pause the printer so it continues to print the egg and seal the rice inside.
You can even print multiple eggs all at once if you need lots!
Step 4: Clean Up Your Printed Rhythm Egg
You will most likely need to smooth out the end of the egg that was on the build plate. I used a file to smooth the rough end with fairly good results.
There you have it - Rhythm Eggs. Now all you need to do is get those kids to shake them all in unison and to the rhythm of the music!!!