Re: Contour Machining, was Optimizing cutting paths, was Traveling Salesman

--- In CAD_CAM_EDM_DRO@y..., rab@r... wrote:

>
> There would seem to be quite large differences in approaches to
> pocketing or contourng - removing material within the boundries of

a

> shape.
> The contouring method where the toolpath follows the shape, getting
> progressively smaller till it reaches the middle seems to be quite
> complicated and difficult to implement well on complex shapes, ie.
> smoothly and with a minimum of tool retractions.

Pocketing is a 2D operation. 3D is called kellering, profiling
surfacing, or just 3D roughing, sometimes 3D cutting strategies are
included with pocketing, but for the most part these are not really
pocketing, but a different animal, and that animal has LOTS of
different varieties. Lathe roughing is also a specialized form of
pocketing.

The contouring method of pocketing is actually quite easy as it is a
series of offsets from the outer contour(a closed planar shape),
something that most Cam software can do fairly well. It gets a bit
complicated with islands, but you just treat the island as a
peninsula with a very small isthmus, and multiple islands as a
peninsula with several areas(nearly islands) connected by very small
isthmi.

The cuts actually originate in the center of the part and finish at
the side walls of the pocket, just reversed from how they are
developed.

Horizontal or zig-zag pocketing is the other major 2D area clearing
method. Like contour pockets, it is a 2D process. Both will result
in tool pickups if blind canyons are created in the contour designs.
Some people use hatching as zig-zag pocketing, if their CAD system
will all them to be interpreted as lines.

Best Regards,

Fred Smith
IMService