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Dimensional Accuracy
The lathe tool is moved by two stepper motors. A single step of the Z axis motor moves the tool 1/72mm, ie 0.01389mm. A single step of the X axis motor moves the tool 1/144mm, ie it effects a change of diameter of 1/72mm. This is not the handiest distance and it means that you cannot machine to every 1/100 mm increment. For example, 360 steps moves the tool 5mm while 361 steps moves it 5.01389mm, not 5.01mm, and 362 steps moves it 5.02777mm, not 5.02mm.
WELturn calculates the distances the tool needs to move to a high degree of accuracy. It then calculates the number of steps which will give a tool movement closest to that required. Because WELturn calculates all distances in absolute terms measured from X = 0, Z = 0, ie the centre of the right hand end of the billet, cumulative errors in part dimensions are avoided.
Where high accuracy is crucial, design parts with dimensions which are whole multiples of 1/72mm.
Accuracy in the Z direction depends solely on the Z axis stepper motor. Accuracy in the X direction depends on the X axis stepper motor AND the accuracy with which the diameter of the billet is measured when preparing for machining. Instead of just touching the tool tip on the surface of the billet, skim the surface under manual control until it is perfectly true. Then, measure the diameter of the billet with a micrometer, a digital one if possible. For highest machined part accuracy, skim the billet until its diameter is a whole multiple of 1/72mm.
If machining is done only with the right hand tool, the resulting accuracy of the finished part will be the best possible on the lathe. If machining involves more than one tool, the resulting accuracy will depend on the accuracy of measurement of the offsets of the tools which follow the right hand tool.
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 this 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.
For the same reason, when measuring the tool offsets, bring each tool tip in the same direction into the relevant quadrant of the microscope cross hairs and make that direction the same as that used for cutting material.
Billet Diameter
Cutting Wide Grooves
Feed Rates
Inches or Millimetres
Plunge and Parting Tool Widths
Speeds and Feeds for Turning and Parting with Indexable Tipped Tools
Surface Finish - Depth of Cut
Surface Finish - Feed Rate
Tool Tip Radius Compensation