Pencil Milling and Other Corner Sequence Machining

Pencil Milling

The pencil milling routine is to finish corners which might otherwise have cusp marks left from previous machining operations. This is ideal for machining into corners where the surface radius is the same as the cutter corner radius. Single pass pencil milling gives a high surface finish ready for polishing. When machining, the toolpath maintains climb milling as default and can be used in conjunction with cutter contact angles. As with all toolpaths in NCG CAM they can be animated alone or with holders. See the pencil milling example to the left.

Parallel Pencil Milling

Parallel pencil milling is an extension of pencil milling, in that the user can determine the number and step-over of multiple-passes either side of the pencil toolpath. This is particularly useful when the previous cutting tool has not been able to machine all the internal corner radii to size. These multiple passes, will machine the remaining internal radii and any additional material left by the previous cutting tool, machining from the outside into the corner. This creates a good surface finish to the true form and can be used in conjunction with cutter contact angles.

Corner Offset Machining

Corner offset machining is similar to constant offset machining . However with this technique, rather than starting from an outside boundary and working in towards the centre of the part, a set of pencil milling passes are created on the features of the part, then a toolpath calculated over the whole part from those features . The toolpath maintains a constant and equidistant surface finish over the whole part . The resultant surface finish in the corner is significantly better than 3D constant offset machining depending on the shape of the part, as the toolpath follows the 3D form and features and can be used in conjunction with cutter contact angles.

Boundary Machining

Boundary machining, machines along an open or closed boundary profile. A negative machining thickness can be used to machine at constant depth below the surface being machined and can be used in conjunction with cutter contact angles.

Boundary machining can be used for the machining of mould tool runner detail, or applied to engraving boundary shapes and text which can be generated using the Windows True TypeTM fonts within the NCG CAM system. The available fonts will depend on the users Windows TM operating system.

Along Curve Machining and 2D Cutter Compensation

Machining along a curve is just as it says - it is the curve that is machined not the surface data. This will allow a toolpath to be generated below the surfaces if needed.

Curves can be read in from the geometry file or extracted from the model. If extracted from the model the curve may be 3D and will be respected as 3D when machined. Curves can also be extracted as 2D curves to be used for 2D machining. These extracted curves contain accurate lines and arcs to get the desired NC Tape file with circular arc moves. There is also a convert curve to boundary function.

Open curves can be joined to get a continuous profile – often in a model it will be several bits of curve that require joining to reduce the number of retract moves.

The along curve machining supports 2D cutter compensation (G41 & G42 or cutter left/cutter right). This enables 2D profiles to be sized on the machine tool; the toolpath has arc fitting for optimised output. Cutter compensation is only available on a 2D curve.

Creating multiple points for start hints allows the user control over the start position and for several curves to be machined within the same operation.

A pass extension will allow the toolpath to be extended out (open profiles) to the cutter can be forced to start clear of the part, for a better cutter approach and cutting conditions.

The optional pass overlap allows the cutter to overlap the starting position (closed profiles) to help reduce a ‘tool line’, giving a better surface finish.