The Tool Length Offset is always measured from the Face of the spindle to the Tip of the Tool. This Length Offset is always constant irrespective of the Part height. Tool Length is also positive allthe time.
We measure this length for each tool & store in the Tool Length Offset Table.
We have to find out the Z-axis Co-ordinate of the Workpiece Table, when we touch the Face of the spindle to the Table. This we can measure by using a Slip Gauge or a Block with known height.
When the Spindle Face touch the Work Table surface, the Z-axis co-ordinate is say -500mm. Then the height of the part to be machined is measured, deducted from -500mm and stored in the Workpiece Offset Table (G54, G55 etc.). e.g. if the workpiece is 100mm in height, then the Z-offset of the workpiece is -400mm. We write -400mm in G54 (G55) table, under Z-axis Offset.
Here onwards, whenever we change the workpiece, we have to change the G54 (or G55) offset as described above.
Tool Length always stays constant, unless new tool is mounted.
Now, when we run the program we write it like follows:
G91 G28 Z0
G91 G28 X0 Y0
G90
M6 T10 (Call Tool & Load in the spindle)
G0 G54 G90 Z100 G43 H10 (Call Workpiece offset, Call Tool Length Offset and Move the Tool Tip 100mm above the workpiece surface, H10 is the location, where the Tool Length is stored).
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smabhyan |