I have used Rast2Vec, (an add-on for Mastercam.)
It worked about as good as you would expect.
However,raster's and pixels will never have the Quailty you need for precision machining, except for artwork.
Take a bit map file,(which is a group of small squares),
then blow it up, and you will see what I mean.
Rast2Vect will try and trace along the jaged edges, and try
an make smooth edges, by using various techniques such as splines. Then there is scaling you must do as well.
Bill