Re: 3-D G-CODE convertion

> Date: Sat, 22 Sep 2001 11:25:50 -0700
> From: Alan Marconett KM6VV <KM6VV@...>
>Subject: Re: 3-D G-CODE convertion
>
>Hi Shabbir,
>
>>From what I understand, anything but a "perfect" arc or circle MUST be
>done as a series of line fragments. So G02 and G03 are out.

The toolpaths developed by the programs like MillWizard, DeskProto, and StlWork consist of planar slices, offset by the tool geometry. The slices are created from a series of short linear moves. This is very similar to the spline approximation that is used in many Cad and drawing programs. Each direction can be defined by one of the 3D arc plane definitions in G-code, G17, G18, G19. G17 of course is the most common use of arcs, as it is an arc that lies in a plane parallel to both the X and Y axis, I usually call these "flat". These would be the waterline tool paths found in StlWork. The other 2 are what I call Vertical planes. They would be like a piece of cardboard standing upright on a vertical mill table, either parallel to the Y axis(Y-Z or G19), or parallel to the X axis (X-Z or G18).

I have had good results with Vector Cam in converting these tool paths into lines and arc approximations of the tool paths. To do it, create the tool path and G-code in the 3D cam software. Import the program into the Vector NC editor, Backplot the program into the Vector CAD drawing(Copy-Paste).

The next step is to use the extensive selection capabilities of Vector to select the tool paths, but NOT the connecting lines that are perpendicular to the direction of the cut at each end of the passes. Once just the tool paths along an axis direction are selected, an Arc-Spline function can be executed and the tool path will now have arcs fitted anyplace along the cut that it makes sense. Reselect the entire tool path and Generate a new CNC program. Typically I have seen about a 50-70% reduction in program length. You do have to remember to add the G18 or G19 at the beginning for the "vertical" arcs.

Controller that support high speed, continuous contouring, and have sufficient buffering will not see much improvement in the processing of the blocks with the arcs added, but older and less capable controls will see a noticeable improvement in accuracy, smoothness, and speed.

Best Regards, Fred Smith- IMService
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