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32 Cards in this Set
- Front
- Back
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Turning Center |
CNC Lathe equipped with an ATC (Automatic Tool Changer) |
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Machining Center |
CNC Mill equipped with an ATC (Automatic Tool Changer) |
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ATC |
Automatic Tool Changer |
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MCU |
Machine Control Unit |
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ACME Screw |
A type of leadscrew used on manual machines which contains backlash, and therefore is not suitable for CNC purposes.
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Ball Screw Assembly |
A screw and nut assembly with steel balls, instead of threads. These achieve 90% efficiency in transmitting torque to linear motion. |
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Ways |
A manual machine implement which uses V-type or dovetail shapes to guide the movement of cutting tools or work holding devices. This is inadequate for CNC because they don't have high-performance seals capable of keeping lubrication in and debris out. They also produce more friction than CNC Guideways. |
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Linear Guides |
A high-tech version of ways used in most modern CNC machines. These units are sealed, with pressurized lubrication systems, and contain low-friction ball-bearings. Available in matched sets, which are removable and replaceable in the field. |
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Servo Motor |
Half motor, half position sensor. |
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Encoder |
The position sensor within a servo motor. Records the amount of rotation a motor makes in degrees. By knowing how far the motor shaft has turned, the MCU can use the lead dimension of the ball screw to calculate the amount the machine axis has moved. The encoder provides feedback to the machine control and if the desired amount of movement is not initially obtained, the machine will instantly adjust the motor's position to compensate. |
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Cartesian Coordinate System |
In machining, this coordinate system tracks movement on an axis or axes using direction and relation, absolute or relative to unity. |
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Polar Coordinate System |
Similar to the Cartesian system, polar coordinates require that positions be identified by defining both an angle and a distance (similar to a vector in mathematics) from the origin to a specific location. |
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Absolute Positioning System |
Coordinates of all positions will be referenced from the workpiece origin (X0, Y0, Z0.) It can often be helpful to think of absolute coordinate as positions or locations instead of distances. |
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Incremental Positioning System |
Specifies a distance from the current position to the next position instead of a location related to the origin. It is important that the correct sign ( + or -) be given to indicated the direction of the incremental distance. |
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Disadvantages to Incremental System |
Programmed Errors will accumulate, and troubleshooting is more difficult. |
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Advantages to Incremental System |
Parts requiring repetitive motions can be easily computed and programmed (i.e. a series of 1" motions for drilling holes all in a row.) |
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Advantages of Absolute Programming |
It is typically less confusing and programming errors are less likely to be made. Absolute positioning is the most commonly used system in industry. |
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Word Address |
An individual program word can be an axis letter with a position (e.g. X3.456) or a code (e.g. G20) Program codes that are executed at the same time are all written on the same line. |
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Codes |
In addition to telling the machine what position to move to, the programmer must also provide the machine with instructions telling it what to do at that position. These instructions are not written in the English language, but rather in code that the machine can understand. |
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G-Codes |
Also called preparatory commands, prepare a machine to engage in a particular mode for machining. For instance, a G1 code tells the machine to feed in a straight line, or linear motion, G0 initiates rapid positioning, G90 turns on absolute programming, G91 turns on incremental programming, and G20 sets the machine to inch units. |
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Modal Codes |
Codes that remain active until cancelled or overridden. Some codes are like switches that when turned on, will remain on, until they are intentionally turned off or overridden with a conflicting preparatory command. For example, if a G0 is programmed after a G1, they cannot both be active, so the G0 cancels the G1 when it turns on. |
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FOUR MAJOR G-CODES USED TO DESCRIBE THE MOST COMMON CNC AXIS MOTIONS |
G0, G1, G2, AND G3.
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Rapid Traverse |
Designated by the code G0. This type of motion is used to position the machine axis very quickly. Only used for preparing and positioning. Accelerates faster than a jet, so be careful! |
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Linear Interpolation |
G1 - Moves the cutting tool in a straight line path between two points. To get from one point to the next, motion may be required in one axis alone or in more than one axis (diagonal movements.) In order to move the tool in a linear interpolated movement, the tool. is first positioned at the start point of the linear cut. Once there, a new program block is commanded with using a G1 and an end position for the movement. A feed rate must also be programmed along with the newly programmed position. |
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G Code Conflicts? |
Not all G-Codes conflict with other G-Codes. |
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Circular Interpolation |
G2, or G3 - causes the cutter's path to travel in an arc. With these motions, CNC machines can cut full or partial circles. These paths are important for milling features such as circular slots, radii on a contour, circular pockets, and for turning features such as spheres, fillets, and radii. G2 is clockwise, G3 is counterclockwise. |
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M-Codes |
Very similar to G-codes, only they are used to turn on and off miscellaneous (auxiliary) functions. For example, M8 turns coolant on, M9 turns it off. M3 starts the spindle motor, M5 stops it. An M6 code activates the automatic tool changer in a machining center, but this code turns itself off automatically when the tool change is complete. An M30 is used to end the program and reset it for the next time it is to be run. |
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Codes other than G and M |
Not all information for CNC machining can be given as G- or M-codes, or coordinate positions. The founders of programming have conveniently created other commands to be named after the first letter of their function. For example, an S-command designates the spindle speed. Likewise, a T-command calls up a desired tool number, and an F-command specifies a feed rate. |
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G0 |
Positioning at rapid feed |
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G1 |
Linear Interpolation |
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G2 |
Circular Interpolation - Clockwise |
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G3 |
Circular Interpolation - Counter Clockwise |
