Cnc machining nm09/2
Writing a program for the 0kuma LB15 CNC lathe
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- Navigate this page:
- 4.21.4 Operators setting up sheet
- Operators setting up sheet
- 4.22 OKUMA LBt5 CNC lathe program format
- 4.22.1 Group 1 — No action
- 4.22.3 Group three — First action
- 4.22.4 Group four — Tool change routine
- 4.22.5 Group 5 —Second action
- 4.22.6 Group six —End action
4.21 Writing a program for the 0kuma LB15 CNC lathe4.21.1 IntroductionThis instruction introduces a standard format for the writing of a part program for an Okuma LB15 lathe using the word address format. Although there are other program formats which will work on this machine, students are advised that the standard program format introduced in these instructions is the only format which will be accepted on this course of instruction. 4.21.2 The jobFor the purpose of these instructions, the job will be a tapered pin as shown below. The program zero will be the face of the chuck jaws. The work is held in the chuck on a pre¬machined step, 40 mm long and with a diameter of 55 mm +/-0.4 mm 
Figure 4.43 4.21.3 The tool pathIn CNC lathe programming where tools tips are round, triangular or any other rectilinear shape, the programming point cam be generated by drawing a vertical line and horizontal line that touch the cutting edge of the insert. 
Figure 4.44 The path the tool will be following in normal feed traverse is shown as a solid line. The path the tool will follow in rapid traverse is shown as a dotted line (see below) 
Figure 4.45 4.21.4 Operators setting up sheetOne of the first tasks in writing a part program for any machine is to complete an Operators Set Up Sheet. The main functions of such a sheet is that it becomes a written copy of what tools and tool offsets are to be used during the machining process. Operators setting up sheetProgramming format
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No action |
(Location pin) No action (57 x 160 m/s round) (Tool 1 = 80 degrees roughing) (Tool5 = 30 degrees finishing) |
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Action set up |
G90 G95 G96 S180
G40 G00 X300 Z300 T0101 M42 G50 S2500 M42 M03
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First action |
G000 X55 Z120 F0.2 M08 G01 X-1.6 G00 Z121 X50 G01 Z20 F0.3 |
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Tool change — finishing |
G00 X300 Z3000 T0100 M09 (Tool 5 = 30 degrees finishing) G00 X300 T050505 G50 S2.500 M42 G06 S200
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Second action — finishing |
G00 X-1.6 Z124 M08 G42 G02 Z120 F0.2 X50
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End of action |
G40 G00 X300 Z300 T0500 M09 M02 |
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For the purpose of standardisation and ease of assessment, this programming format is to be strictly adhered to by students
4.22.1 Group 1 — No action
( ) As an ISO standard any information in brackets is man readable information to which the MCU will not react to:
4.22.2 Group 2 — Action set up
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G90 G95 |
G90: The G90 command instructs the MCU that all tool path coordinates have been expressed as absolute coordinate values.
G95: Given that convention has feed on a lathe expressed as mm/rev, G95 will ensure this mode of feed.
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G96 S180 |
G96: This command maintains a constant cutting speed throughout the cutting operation. When G96 is evoked the MCU will automatically increase or decrease spindle RPM to main a constant cutting speed with each change in workpiece diameter.
S180: Although S values generally refer to spindle RPM, in this case when associated with G96, S 180 sets the constant cutting speed to 180 m/min.
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G40 G00 X300 Z300 T0101 M42 |
G40: The G40 command when used at this point of a program is a precautionary move to ensure that any Tool Nose Radius is compensated is cancelled. More about Tool Nose Radius compensation shortly.
G00 X300 Z300: This command instructs the MCU to drive the tool slide to the Machine Home position G00 X300 Z300. This is required at the beginning of each part program as well as during all too change routines.
T0202: This command calls up TOOL No.1, (T0101) and applies the TOOL OFFSET No.1, (T0101). The OFFSETS for all tools to be used are established and registered in the MCU prior to machining.
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G50 S2500 M42 |
G50: The G50 command is a ‘speed limiting’ command which prevents the machine chuck from exceeding a specified RPM. This is use particularly where large diameter work is required to be faced while a G96 command is in force. Without a speed limiting the G96 command would allow a workpiece being faced to reach maximum RPM as the tool reaches the centre of the job.
S2500: When used in conduction with the G50 command S2500 specified the maximum RPM which will be reached. In this example 2500 RPM.
M42 (M41): The RPM ranges on the OKUMA are controlled via a preselect gear box which is coupled to the electronic speed control unit. M42 sets the machine in high spindle range. M4l sets the low spindle range.
M03: This instructs the MCU to drive the spindle in a clockwise direction.
4.22.3 Group three — First action
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G00 X55 Z120 F0.2 M03 |
G00 X55 Z120:
This command will drive the tool to the ‘initial stand off’ position somewhere close to the starting point but still off the workpiece.
FO.2 : All ‘F’ words relate to feed rate, in this case a facing feed rate of 0.2 mm/rev. Because feed command are modal any new feed command will cancel any previous command, for example, the G01 Z20 F0.3 command will cancel the current F0.2.
M08: This command is a programmed ‘coolant ON’ command.
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G01 X-1.6 |
At this point of the program the co-ordinate points of the tool path is entered. A widely accepted practice is to first machine the workpiece to the correct length by a series of facing cuts which, as shown in this example, extend 1.6 mm past the centre of the work in diameter terms as indicated by the minus (-) value of -1.6 mm.
4.22.4 Group four — Tool change routine
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G00 X300 Z300 T0100 M09 |
G00 X300 Z300: Drives the tool slide back to the machine home position.
T0100: Cancels the tool offset for Tool 1. T01 identifies the tool number while the 00 cancels the offset.
M09: Turns the coolant OFF.
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G00 X300 Z300 T050505 |
G00 X300 Z300: Confirms the machine home prior to a tool change.
T050505: In this particular example a finishing tool is being called up. Because the finish cut will involve a taper or a contour, Tool Radius Compensation must be applied. The order of instructions are:
T05 — Call up Tool 5
05 — Call up length offsets 5
05 — Call up value Nose Radius for Tool 5
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G50 S2500 M42 |
G50: The G50 command is a ‘speed limiting’ command which prevents the machine chuck from exceeding a specified RPM (S2500).
G96 S200: Resets the constant cutting speed to 200 m/min.
4.22.5 Group 5 —Second action
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G00 X-1.6 Z124 M08 |
Rapid traverse to initial stand off position and tum the coolant ON.
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G42 G01 Z120 F0.2 |
G42: In the next section of this guide the topic of Tool Nose Radius Compensation will be discussed in some detail. At this point of time it is sufficient to state that Automatic Tool Nose Radius Compensation must be applied during a motion command at using either a G42 or G4l command.
G01 Z120: This is a motion command during which the Radius compensation is applied.
F0.2: This feed rate of 0.2 mm/rev over rides all previous feed rate commands.
4.22.6 Group six —End action
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G40 G00 X300 Z300 T0500 M09 |
G40: At the end of each action you are required to cancel all Tool Nose Radius Compensation with a G40 command.
G00 X300 Z300: At the end of the cutting routine drive the tool slide to the machine home position.
T0500: Cancel the Tool No.5 and Tool Offset No.5 with the command T0500.
M02: End of program —go to starting block.
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