Here’s a handy tool that isn’t talked much about – the tapered reamer.  It is great for opening up holes.  While using an No 11 X-ACTO blade is an easy way to bore out a hole in, say, polystyrene, as the hole gets bigger it becomes less round and then becomes a jagged mess.  The reamer pictured above will do diameters from 1/8″ to 1/2″.  It makes very round holes by simply turning it clockwise.  The more it cuts, the bigger the hole gets.

The hole created will have the same taper as the reamer.  To counter this, I insert it the opposing way into the nearly-finished hole and clean-up the bore on the other side.  If the plastic material isn’t too thick, the resulting double taper on the hole isn’t noticeable.  I have found that if the hole looks a little out-of-centre as I am boring it, I can favour one side of the hole to remove material only there.  To do this, I make cuts in the desired direction using only about a 90 degree turn (to the right & back left) in succession.  When it looks like I’m back on centre, I can then resume the full turning action.

I only use this on polystyrene plastic, but it would also be ok for wood and soft metals.