This finishing technique is best suited to machining areas, which require a constant stepover and works well on near-vertical faces.
Spiral toolpaths mill a feature in a series of offsets towards the feature center. The initial pattern is specified by taking the stock boundary, the feature boundary or the curve specified in the Boundaries tab. To use the stock boundary, click Use stock dimensions as boundary on the Boundaries tab. This will result in an initial square shape to the toolpaths. The next and subsequent toolpaths are obtained by offsetting the initial shape in 3d (along the surfaces being cut). This differs from 2d spiral operations which offset the initial shape in 2d and then project this shape onto the surfaces. Also, there is no spiral-out with a 3d spiral operation.
Select Use part surfaces as boundary in order to use the silhouette of the part surfaces as the initial boundary shape as shown in the simple figure on the left. The figure on the right shows the toolpaths that would result if Use stock dimensions as boundary were used instead.
The Spiral option on the milling attributes page will eliminate the stepover between the offsets, and morph the pattern into a continuous spiral. With the Spiral option checked you will get the result shown below. You can see that this minimizes the number of tool retracts and converts the original closed contours into one long spiral.
With the Spiral option un-checked you will get the following result. Notice that there is a retract between each contour.
The regions of the spiral can be controlled by specifying a slope angle on the Boundaries tab. In the example below, the slope angle is set to 30 degrees. Regions with slope greater than 30 degrees are avoided.
Boundary curves can also be used to control the shape of the spiral. All of these options are accessed by clicking the Curve options button on the Boundaries tab. By specifying a boundary curve, this shape is used as the initial contour of the spiral.
The boundary curve is clipped against part surfaces as shown in the figure below. If the curve is entirely outside of the stock, the silhouette of the surfaces is used as the boundary curve.
If the operation is specified as a boss, then boundary curves determine regions that will be avoided.
If the operation is specified as a pocket, then the boundary curves represent the shape of each region. Any island curves are avoided. In the example below, the operation is specified as a pocket with three boundary curves. The lower left region also has a circular island region.
The Z height of any boundary curve is ignored. This means that the curve can be above, below or even inside of the part.
The total offset option of the Boundary curve dialog is disabled for 3D spiral milling.
Curve allowance is the same as described for 2D spiral milling.