Interpolating Axes On Manual Machines

 A skilled operator can machine a variety of complex parts on a manual machine tool with the aid of a digital readout, but the limits of what a DRO-equipped machine can do have always been clear. Manual machining can’t coordinate the motion between two axes. That means a DRO can be helpful for straight cuts, but it takes CNC to cut along curves.

Or maybe not. Heidenhain (Schaumburg, Illinois) now offers a DRO, the “Positip 880,” that can be used to machine circular arcs. The device does not provide coordinated control between axes—it’s not a CNC—but it does let the user manually achieve this coordination through the use of a clever trick. Once the user has entered the desired tool path into the control—a tool path built out of straight lines, circular arcs and bevels—the DRO presents this tool path on the display as a target for the operator to follow.

A point on this display marks the tool location. The intended path is bracketed by two parallel lines that mark the width of the user-definable tolerance band. Moving the machine’s handwheels moves the tool location on the screen by an exaggerated amount, because the scale of the display is magnified. As long as the operator can keep the point on the screen between the two tolerance lines, the machine will cut the profile to the intended accuracy.

An operator can control either or both of the manual machine’s handwheels while cutting in this way. On a milling machine, the operator may choose to have one axis feeding steadily at some slow rate while only the other axis is maneuvered by hand to keep the tool on track. On a lathe, where the handwheels are closer together, the operator may turn both of the wheels at once to follow the path on screen (using the machine tool like a metalcutting Etch A Sketch).

This is not a high-productivity solution. However, the capability may bring greater usefulness to some machines that have long been in service. For the shops and toolrooms that use manual machines to make a variety of one-time or short-run parts, this feature of the DRO increases the scope of what a manual machine can do.