Tapping Teflon

As an experiment I tapped a 6-32 hole in Teflon.  I went about 1/2".  When I screwed in a screw, it was pretty well held. I would not rely on to hold much load but 1/2" depth and I could not pull it out. 

At 1/8" I could easily pull it out.  Is that just a cumulative hold of a bunch more threads and did I not get the first few threads exactly square.  These should have been the squares.  I turned the tap in a drill press chuck with the Teflon in a vise.  The rest of the threads I made with the tap in a power screwdriver.   

I am inclined to use acetal instead for places where I need low friction.   Acetal threads are rock solid.  I can also order black acetal,  which will go well with the overall appearance of a black carbon fiber composite mount.