This is a string shooter that I designed. I first saw a string shooter at a Maker Faire in Madison Wisconsin. The string shooter I saw in Madison was made by the Madison Waldorf School Maker Club.
After I decided that I wanted to make one I found a couple of DC motors in a box in my garage and built the design around them. The motors I use were originally from inkjet printers. When my string shooter is running the motors are turning at about 5000 RPM.
I connect the ends of the string together to form the loop by gluing the ends together with CA glue (Super Glue). I show the process in the YouTube Video linked below.
I wrap loops of bicycle inner tube around the 3D printed wheels to give them a little traction on the string (shown in the video linked below).
There is a picture of the yarn that I found worked well with my setup. It is yarn intended for knitting dish cloths. (Lily, The Original Sugar and Cream, Article 930H)
My string shooter works well with the funnel without the slot in the side. The funnel with the slot in the side is only needed if you want to be able to replace the string loop with a pre-made string loop (see the video for more details). Without the slot you need to thread the string onto the machine then connect the ends of the string together to form the loop. The wire loop in front of the funnel is only needed when using the funnel with the slot in the side. Without the wire loop the string will occasionally find the slot and fly off of the machine
All of the parts (except the bent wire) are included in the OpenSCAD design file. You can easily modify the thickness of the material for laser cutting in the OpenSCAD file (modify the "t_material" variable.) I printed all of the parts with 100% infill. They are very thin parts so it doesn't make sense to skimp on the material.
I made a YouTube video of the string shooter in action and I discuss the two types of funnels and show how I glue the yarn into a loop.