John,
Getting a bit philosophical here: I think it's generally true to say that the smaller "round stuff" is quite readily available as off-the-shelf materials … and your mill could make 'most anything else.
Most designs would need some "production engineering" to avoid the use of difficult turned parts, but I think you would be able to produce an engine of some sort.
A rotary table for the mill might be a wise investment [and perhaps a good project]
MichaelG.
.
P.S. … Welcome aboard !!
Edited By Michael Gilligan on 06/07/2015 09:17:17