Safely cutting down a seatpost I want to shorten my seatpost it fouls the non-OEM kickstand on my folding bike when lowered. 


What is the best way to cut a (33.9mm alu) seatpost? Can I just use a rotary plumbing pipe cutter? The edges of a seatpost appear to be deburred or smoothed, what's the best way to achieve this?
There's no minimum insertion markings. Is there a rule of thumb in their absence?
I agree with @ojs answer on point (1), you can just cut it with a hacksaw but with the exception of point (2) "the common consensus seems to be at least 5 cm of insertion" - the standard minimum insertion mark on a seatpost is 100mm, double this. You may get away with a bit less, like ~90mm or maybe even 80mm but 50mm would seem very much on the short side to me.

The general idea is that the seatpost should extend a decent amount beyond the bottom of the top tube. 5cm is unlikely to accomplish this on most bikes. He may have been thinking inches.

I'd leave this as a comment on his answer rather than an answer on its own but I don't have the reputation and it is an important issue for safety.