CNC West Dec jan 2019

CNC WEST December 2018/January 2019 www.CNC-West.com 57 the Feb/March 2018 issue of CNC West. If you’re not familiar with it, I suggest visiting the CNC West online archives. “Points” are the points a toolpath uses to move between. These moves can be straight lines or arcs depending on the smoothing settings. Some machines move best and produce better surfaces with very tiny straight lines while other machines struggle to process the amount of code required when process- ing tiny straight lines and will produce poor surfaces. Machines that struggle with processing lots of code benefit from smoothing because they process arcs and longer straight lines more efficiently. Tolerance and smoothing have many of the same effects on 3D toolpaths as they do with 2D toolpaths, with a few dif- ferences. First, tolerance drives the mesh tessellation as discussed earlier. Second, smoothing only works with 3D toolpaths that are aligned with the G17(XY), G18(XZ), or G19(YZ) planes. For example, a parallel toolpath that has a pass direction aligned to the X or Y axis will benefit from smoothing/filtering because most of the movement is done in either the G18 or G19 planes so G2/G3 arcs can be applied, reducing the code size significantly. A toolpath such as ramp Boundary” with the tool containment set to “Center on Boundary” is the most effective way to get the entire bottom edge of a sloped surface machined. However, when a downhill slope meets a vertical wall it doesn’t take much of a triangulated edge to stick out of a vertical wall, making the CAM think there’s something down there that needs to be machined. The bigger the toolpath tolerance, the bigger the triangles are, and typically the worse the toolpath waterfalls outside of the containment boundary. Reducing the toolpath tolerance will sometimes fix most of the noisy water- falling toolpath but reducing the toolpath tolerance may also create more toolpath points (more G-Code) than desired. Figure 4 shows the toolpath points cre- ated over a surface. The most effective edit I’ve used to eliminate a noisy waterfalling toolpath is to add a negative offset that is equal to the toolpath tolerance. For example, if my toolpath tolerance is .001in then I’ll input -.001in as the “Additional Offset” in the “Passes” tab in Fusion 360 or other HSM tools. This technique essentially excludes any protruding triangulated edges along the vertical walls from toolpath calculation. P oints and smoothing/filtering affects: I discussed smoothing and tolerance and how they relate to part geometry and machine movement in is always moving in X, Y, and Z simultaneously, so smoothing has little to no effect on the point distribu- tion or code output. In summary, smoothing/filtering works by analyzing the cut path and fitting long lines or tangent arcs where possible to replace short line moves. A nother detail to consider about points with 3D surface machining is point distribution. Note the very consistent point spacing and distribution in Figure 4. It’s a good generality that evenly distributed points over the surface topology will produce nicer, more consistent finished surfaces. Manipulating toolpath tolerance and smoothing settings can change point distribution, but toolpath type and the driving geometry are most often the key contributors to consistent point distribution across surface topology. M y overused saying “the devil is in the details” couldn’t apply more appropriately to anything than it does to 3D surface machining. I hope the informa- tion in this issue will help you be more productive and produce better parts. I look forward to digging even deeper into this topic in the coming months. Figure 2 Figure 3 Figure 4