i have just finished slicing off sprue from 1/144 missiles. it was a bear to do, until i figured out how i should do it. i got a block o wood about 1" by 4" by 6" and cut on the edge of the block of wood. this way the missile fins dont get in the way or trimming.
you can also use a block of wood to raise any kind of part off the bench so you can hold it properly.
hope this helps