Just to be safe I want to clarify that MACH is fully capable of true 3d work, however the DXF importer will not handle 3d DXFs.
So, that being said, for most true "3d" work, CAM software is the way to go. There is a multitude of CAM software out there, you need to choose one that best fits you needs and budget. I would recommend downloading LazyCAM from the MACH support site though. It is currently in development, but will end up being a powerfull package, just as MACH has been. Did I guess right, were you using a DXF to bring the part into MACH?
One more question. Is this part truly 3d or just 2 1/2d?
Hope that helps a little.
Thanks,
Rob