Today I discovered a trick that makes it easy to feed a new spool of filament into the Creality Ender 3 (my 3D printer). This should work for any 3D printer that feeds filament to the extruder through a tube.
The filament feeds through a small hole that opens fully when you partly close that spring shown above.
The problem is that the filament is very close to the same diameter as the insertion hole. That means you need to hit the target precisely for the filament to actually load, otherwise it just bumps into the inner edges of the tube. The filament is probably bent in a circle from sitting in its spool, which makes this problem worse.
The solution is the narrow the tip of the filament.
Take a pair of wire cutters and snip the leading edge of the filament at a sharp angle. Pre-heat the print head and push a couple cm’s of filament out and this sharp edge will melt off.