Filament Spindle v1.1

Rob (tinkerings) asked me to make a crystal spool for his crystal Cupcake and I thought that I'd try to make a few improvements to:

1. Make the spindle easier to load and disassemble.
2. Improve the coupling in between the spindles and between the spindle and the bot.
3. Try to prevent binding by keeping the filament from getting under the the spool.

I've made the spindle case keyed so they lock together when stacked. I've also added a top tray that the Cupcake sits on that is keyed as