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Set the Tool Offsets

WELturn guides you through the process of measuring tool offsets.

All lathe tool tips must be at centre height before any offsets are measured.

The essential tool for measuring offsets is a tool seting microscope.

What are Tool Offsets?
Ideally, when any lathe tool is clamped to the machine its tip should occupy the same position in space as the right hand tool. In reality they do not: just exchange a right hand tool for a left hand tool to see this. The tip of the left hand tool is some distance away in the X and/or Z directions from where the tip of right hand tool was. These distances must be measured accurately so that corrective movements, called offsets, can be applied by the machine controller. Immediately after a tool change, WELturn moves the new tool by an amount equal to its X and Z offsets so that its tip will be where the right hand tool would have been. This ensures that the new tool starts cutting at the right place.

The right hand tool never has an offset correction applied to it. It's tip position is the datum from which the distances to all the other tool tips are measured: its like the zero on a ruler.

If a lathe tool tip is to the right of the right hand tool tip by, say 10mm, it must be moved 10mm to the left to bring its tip into the correct machining position. The offset is -10mm.

If a lathe tool tip is to the left of the right hand tool tip by, say 6mm, it must be moved 6mm to the right to bring its tip into the correct machining position. The offset is +6mm.

If a lathe tool tip is nearer the lathe centre line than the right hand tool tip by, say 1.5mm, it must be moved 1.5mm away from the lathe centre line to bring its tip into the correct machining position. The offset is +1.5mm

If a lathe tool tip is further away from the lathe centre line than the right hand tool tip by, say 2.1mm, it must be moved 2.1mm towards the lathe centre line to bring its tip into the correct machining position. The offset is -2.1mm

The offsets are automatically stored by WELturn in a Configuration Settings file at C:\WELTURN\PROGRAM\WELturn.ini. This file can be edited in a text editor such as Notepad. This means that small alterations to the offsets can be made manually if measurement of a machined part shows that axial (Z) or diametral (X) dimensions are not quite right because the offset measurements are not spot on.

If you do manual editing, you need to think carefully about whether to increase or decrease an offset value and by how much. X offset changes need special care. If a machined diameter is, say, 1mm oversize, the offset needs to be reduced by half that amount, 0.5mm, because X offsets are radial corrections.

There is some backlash in the X and Z leadscrews. If cutting is done in both the + and - directions there is likely to be some dimensional inaccuracy in the part due to backlash. If at all possible, ensure that the tool is always fed into the billet in the same direction, eg always cutting in the -X and -Z directions.

In the same way, when measuring the tool offsets, bring each tool tip into the relevant quadrant of the cross hairs of the tool setting microscope in the same direction and make that direction the same as that used for cutting material.

Clean Down at Manual Tool Change
Tool Setting Microscope
Tool Tip Radius Compensation