CNC machining starts with a piece of metal called a billet - essentially a
lump of metal. The billet could have been cast, forged, or rolled.
It is put into a fairly standard machine tool, that has had position sensing and
motors on the control knobs installed.
What's wrong with CNC machining?
Not much - although for some things forging may be better.
Many machinists think that CNC machining wastes metal, and it's difficult to
argue with that in some respects. What's left is metal shavings, which are
fairly value-less in resale (even for scrap). In today's steel-starved markets,
that is significant. Forging uses most of the metal, by contrast. A bit of metal
can seep into cracks between the tool and die.
CNC machines are complex - full of servo-mechanisms and measuring
technology that can measure to 0.005mm (0.0001") while covered in oil. According
to manufacturers, a CNC machine has a minimum of 6 motors, meaning that
operating costs can be high.
The advantages are too great to ignore
The truth is, though, that CNC offers a world of advantages over forging.
It's fast, and the control is a wonderful thing on multiple -run projects.
Once your computer is programmed, CNC can make a perfect run of cuts and shapes
without much of a chance of failure. If you only plan to build a small number of
items, CNC is just the thing for parts with a complicated shape
A book I recommend to anyone interested in CNC machining is Machining And CNC Technology. This
book is a student textbook, and it's expensive, but it comes with a CD-Rom as
well as a dense, well written text.
It's the first text written to fully integrate basic machine tool and
CNC concepts throughout. Beginning in the first chapter, the differences between
manually-operated and CNC equipment are shown and compared. The text is written
for introductory courses, and does not assume previous machining background on
the part of readers. Part I discusses the basics of today's integrated
manufacturing world. In Part II students learn to safely set up and run manually
operated equipment, always with the goal of transferring their skills to CNC
systems. This part covers setups, safe operation, faultless program tryout and
program writing, both with command codes and using CAM. CAD/CAM exercises are
provided on CD-ROM, using the Mastercam® software program (student version).
Finally, Part IV focuses on the future, highlighting technologies that have
changed, and will continue to change, our manufacturing world.
An Introduction to
CNC Machining and Programming
is a less expensive, but still informative book. This unusually practical
introduction to numerical control technology fully explains the most recent
developments in machining and programming. Logically organized, CNC Machining
and Programming begins with a review of basic concepts and principles and moves
on to tooling, work-holding, machine setting, speeds and feeds, and part
programming before concluding with a discussion of advanced techniques. Both
beginning and advanced readers will find a wealth of new information in this
complete overview of CNC.