Contents - Index

Inches or Millimetres


WELturn can accept and process NC code files where the units of measurement are inches (in the UK, Imperial units, in the USA, US measurements). This capability was added to WELturn in December 2002 at the request of model engineers.

This topic deals with how Imperial units are handled by WELturn.

Changing from Metric to Imperial
Click on the Lathe tab at the top left of the screen. Check or uncheck Use Imperial Units, as required. When WELturn is restarted it defaults to the last units used. The units in which it is working are displayed in the title bar at the top of the screen.

If the units are set to Imperial and you select a metric code file for machining, WELturn automatically changes to metric units.

If the units are set to metric and you select an Imperial code file for machining, WELturn automatically changes to Imperial units.

The only time you need to manually select metric or Imperial is when you require a particular read-out in the "Use the Keyboard to move the Tool" or "Set the Tool Offsets" screens.

Resolution
The smallest movement a tool can make is 0.0005468 inches, just over half a thou. This strange number is a function of the mechanical design of the lathe leadscrew pitch and stepper motor gearing. In the manual tool movement screens, the distance moved is displayed to four decimal places: thus 0.0005468 is displayed as 0.0005. This display increments in what appear to be strange intervals: keep in mind that these intervals are multiples of 0.0005468.

Tool Offsets
When measuring the tool offsets, WELturn can be set to either metric or Imperial units, it does not matter. The offset measurements will be displayed in their metric or Imperial equivalents. The only time you need to take the units into account is when asked to enter the width of a parting tool: the figure entered must be in the units in which WELturn is working.

Feed Rates
Imperial feed rates can be in inches per minute or inches per revolution. You do not have to tell WELturn which units are being used.
  • If the numerical value of a feed rate is 0.040 or greater, then WELturn assumes inches per minutes.
    ·
  • If the numerical value of a feed rate is 0.038 or less, then WELturn assumes inches per revolution.
    ·
    Because the precise changeover point from one set of units to the other is an awkward number, you are advised not to choose a numerical value between 0.038 and 0.040

    X, Z, R, F, H Inch Measurements
    In all cases these are declared in figures of appropriate magnitude for the job, the material, the lathe tool and the particular G-code line being programmed. In all cases, decimal values must be used, eg 3.625 and not 3     5/8 (three and five-eighths).

    NC Code File Format
    WELturn recognises a metric or Imperial NC code file from the characters in its very first line.
  • The first line of an Imperial code file must consist only of a percent sign in the first column immediately followed by a letter "eye" (%I or %i), nothing else (it is not case-sensitive: the letter can be i or I).
    ·
    (The first line of a metric code files must consist only of a percent sign (%) in the first column, nothing else.)

    The last line of all code files must consist only of a percent sign (%) in the first column, nothing else.

    In all other respects, metric and Imperial NC code files have identical formats. The format is described in the topic     CNC File Specification.