Here's a photo of the first of a series of modifications I'm making to a Bachmann On30 4-4-0.  My goal is to make it more representative of standard Baldwin narrow gauge 4-4-0s of the late 1800s. 

This photo shows new fluted steam and sand domes I turned in brass, and a new Precision Scale Stevens stack.  I also cut off the smokebox extension.

I'll post additional photos as progress is made.

Matt - CNC stands for "Computer Numerical Control" - essentially, a computer drives stepper motors attached to each of the X-Y-Z axes following a program written in g-code.  The computer can cut things with far greater precision than a human being.  The radial boiler cutouts on the domes are a good example.  While this could certainly be done by hand, cutting a circle/radius requires precise manipulation of both the X and Y axes simultaneously.  A good machinist could do it - but I'm not a good machinist.  hehehe

Something simple like this could also be done with a hand file and some sandpaper - but my motto is "never use muscles when there's an electric motor that will do the same job."

As to Harbor Freight, it wouldn't do what these tools will do.  First off, Harbor Freight's is not CNC.  Also, when buying machine tools such as these, precision mechanisms are all important for maintaining good work tolerances.  Less expensive tools are known for sloppy fits producing large tolerances in the work being produced.  Again, a good machinist can compensate for less than stellar tools and produce good work on them, but at a higher cost in man-hours and patience (not to mention knowledge and experience).  Like I said, I'm not a good machinist. 

MHO for whatever it's worth.