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 well and has slots for the bolt heads on the side of the bot. You can pop the tray off easily to get to the spool, and the top of the spool is secured by a single M5 bolt so it's easy to disassemble to reload. I've also added some PETG fingers around the base of the spool in an attempt to prevent the filament from getting under the spool and binding.