The Tube Sharpener is a tool to create a chamfer at the end of a PTFE tube as used for PTFE liners in hotends.
It can be made of a 8 mm steel rod (25 mm long) drilled on one side with a cone. Make 2 slits on that side with a saw or a Dremel.
Bore a 2.5 mm hole into the center of the other side, 15 mm deep. Cut a M3 thread into that hole and screw a 40 mm M3 threaded rod into it.
(Click image to expand.)
The 3 mm rod fits into a Dremel.
At 30,000 rpm this tool makes a very smooth chamfer to any PTFE tube.
Beware of your fingers when holding the tube! Best put a washer between the tool and your fingers.