DIY Dremel CNC 8mm

This is a remix of the oringal DIY Dremel CNC for 8mm rods and the corresponding linear bearings (LM8LUU) as I still had some of these lying around.
Also includes some minor improvements of e.g. the spindle carriage and other parts.

I also added a mount for attaching a proxxon FBS240E to the spindle mount.
This makes it easier to upgrade / switch to a spindle later on - which is what I'm planning to do if this turns out ok.

Update 2019-09-19:
I finished building the CNC and tested it a bit - it works quite ok, but it needs some improvements to reduce wobble and resonance.
I noticed that the spindle mount wobbles quite a bit on the vertical linear rods. So I redesigned it in a way which allows the adjustment of one of the two linear bearings using two 3mm screws. I haven't had time to test it yet, but after the assembly the spindle mount does not wobble anymore.

I also added bigger X-Axis Carriages. They use 2 LM8LUU linear bearings instead of only one. They help to reduce