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Some general terminology related to CNC machining technology.
(Under Construction)
Ball End Milling Cutter - A milling cutter that has a rounded cutting
diameter at its end that is equal to the cutting diameter.
Closed-Loop System - A positioning system that can use either step motors or
servo motors ( basically just a DC or AC motor ) with an added optical encoder attachment
to the motor shaft. The motors receive movement commands from the computer.
The optical encoder then sends this movement information back to the computer to
verify that the correct movement was produced. Hence, the computer has a record at
any instant of the actual or real position of the mechanism. This type of system can
achieve much higher positioning speeds then the open-loop kind without losing track of the
position.
DXF file - Drawing eXchange Format file
that was created as a standard to freely exchange 2 and 3 dimensional drawings between
different CAD programs. It basically represents a shape as a wireframe mesh of x,y,z
coordinates ( vectors ).
Encoder - Typically an optical device that consists of a disk with 100
to1000 holes on its periphery. The most common is the incremental encoder that has a
small LED light source on one side of the disk with a diode detector on the other to allow
the disk rotation to be monitored in discrete incremental steps. Hence, a full
revolution can be broken up into 100's or even 1000's of position steps.
G-Code - The standard machine tool language around the world. It
generally consists of specifing the x,y,z (and a,b or c ) coordinates that the machine is
to move to. Such movement can be linear, circular or even special drilling
operations. It is the universal language of all modern machine tools ( mills,
lathes, edm machines etc.).
HPGL - Hewlet Packard Graphical Language
that was originally created to send 2 dimensional drawing information to pen plotters, but
has since become a good standard for the exchange of 2 dimensional drawing information
between CAD programs.
M-code - The standard machine tool codes that are normally used to switch on
the spindle, coolant or auxillary devices. They can also be used for G-code program
control such as repeating the program or ending it.
Open-Loop System - A positioning system that generally uses step motors.
The step motor amplifier receives signals from the computer and makes the commanded
movements. This movement information is NOT sent back to the computer to verify that
the movement was correct. Hence, if the positioning mechanism stops unexpectantly
the computer will lose track of the mechanism position. Note: Under normal
cases this does not happen and the position is always recorded correctly.
PID - Proportional Integral Derivative acronym that is the mathematical
control method used in a standard closed loop servo system.
Repeatability - The smallest distance that can be repeated by a machine
movement. For example if the repeatability is specified as 0.001 inches and a
movement from X coordinate 0.000 to 1.000 and back to 0.000 then the position would be
within 0.001 inches of 0.000.
Servo Motor - A motor that is typically a brush or brushless DC type with an
optical encoder attached to it. It is used in what is called a Servo Loop system
where positioning information is constantly tracked by minimizing the error between the
commanded and real position.
Step Motor - A motor that derives its motion by receiving input signals (
pulses) in a very specific sequence. The most common type is one that rotates 1.8
degrees for each input pulse. This provides a very simple way of controlling motion
very precisely with the use of common digital logic circuitry.
STL file - Stereo Lithography file format that has traditionally been
associated with Stereo Lithography prototyping machines, but is now also being used to
represent 3D surfaces for CNC tool path generating programs.
Tool Path - A series of vector coordinate positions that define a cutting
path. This cutting path can be a simple 2D or sophisticated 3D ( even 4D or more)
path used to machine out the shape of a desired part.
Vector - A line that has both length and direction. It is usually
specified by a starting x,y,z coordinate position and ending x,y,z coordinate position.
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