Be very careful when using or creating heat with stem materials. Vulc tends to suddenly 'boil' or melt and lucite (acryliic) becomes unstable.

Your preferred method should be the one that scratches or scores the interior of the stem the least. The more rough surface inside the stem the more trapping of tars, moisture and taste (that can becomes foul).

Pipe manufacturers all use drill bits, often (usually) with a jig to hold the stem in place. I have seen one use a sandpaper string to clear debris (super fine grit).

Remember, with any tools that the pressure alone can cause damage to the stem.

Good Luck.

Pete