1.75/6 mm Contractible spool for filament coils

Big thanks Heinz Spiess for sharing your design.

I like idea and design of original but it is not suitable for me.

This thing the same as original except two changes:

• Central hole in hub changed to 6 mm but external radius of hub the same.
• Holes for filament fix changed from 3mm to 2 mm (for 1.75 mm filament) but mounting holes unchanged 3 mm.

I made minimal changes in .scad file an describe changes in comments