What Is CNC?
Computer Numerically Controlled (CNC) machines are capable of carving complex
patterns out of a wide range of materials. Essentially CNC is the attaching
of a computer-controlled device that allows the user to program a part, and
have the computer drip feed the information straight to the machine. The information
is coded into what is called G-code, which gives the programmer control over
every aspect of the machine such as the starting point, stopping point, speed,
cut rate, ect.
Stepper Motors: How They Work
Stepping motors come in a wide range of angular resolution. The coarsest motors
typically turn 90 degrees per step, while high-resolution permanent magnet motors
are commonly able to handle 1.8 or even 0.72 degrees per step. With an appropriate
controller, most permanent magnet and hybrid motors can be run in half-steps,
and some newer controllers can handle smaller fractional steps or micro-steps.
All this basically means is that a stepper motor has a center rotor that spins
encased in a cylinder that has several (usually 20) teeth, which are also commonly
called windings. If a controller sends an electrical signal to one of the teeth,
the rotor (under no load) will snap to that point. If the next winding in sequence
is then given the signal, the rotor turns to that position. It is possible,
however, to energize two windings at different amounts and micro-step the drives.
Benefits of Retrofitting
If you compare the costs of retrofitting versus purchasing new equipment, the
benefits are in favor of retrofitting by a long shot. A typical new CNC mill
might run $30,000-60,000 while a similar retrofitted mill might cost a third
to a sixth of that amount. Another important benefit is accuracy, which new
computer controls can handle up to ten times more accurate signals than other
OEM CNC controls. The downside of retrofitting is that it is not always easy
to find suitable machines for the process as they are often thrown out or junked
due to their age. Assuming a person was comparing the two options for a new
machine purchase, retrofitting can be quite a cost-saver.