DXF Offset Pocketing loops

Some basic pocketing loops generated on the train today.

Using pycam's revise_directions() function it is possible to clean up the DXF data and classify polygons into pockets and islands.

There's a new parameter N_offsets

  • N_offsets=1 generates just a single offset at a specified offset-distance.
  • N_offsets=2... generates the specified number of offsets. Possibly with an increment in offset-distance that is not equal to the initial offset-distance. This happens e.g. when we want the final pass of the tool to be one cutter-radius from the input geometry but the material is difficult to machine and we want the "step-over" for interior offset-loops to be less than the cutter-radius.
  • N_offsets=-1 produces a complete interior pocketing path. Offsets are first generated at the initial offset distance and successive offsets are then generated at increasing offset distance until no offset-output is generated.

Todo: Nesting, Linking, Optimization.

There's no nesting among the loops here. The algorithm will have no clue in what order to machine the offset loops. A naive approach is to machine all loops at the maximum offset distance, then move one loop outwards, etc. But this is clearly not good as the tool would jump between the growing pockets during machining. Nesting information should be straightforward to extract from the voronoi diagram during offset-generation. The nested loops form a tree/graph, which we traverse in some suitable order to machine the entire pocket.

Also, there is no linking of these loops to eachother. For a machining toolpath one wants to link the offsets to each other so that the tool can be kept down in the material when we move from one offset loop to the next. A simple algorithm for linking should be straightforward, but I suspect something more involved is required to prevent overcutting with sufficiently complex input geometry.

When one has nested and linked offset paths, in general there still will remain "pen-up", "rapid traverse", "pen down" transitions. An asymmetric TSP solver could be run on this to minimize the rapid traverse distance (machining time).

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