CNC West Feb March 2019

CNC WEST February/March 2019 www.CNC-West.com 63 Z slice: Z slice toolpaths apply toolpaths at distinct depths based on the step-down distance specified in the toolpath parameters, just like the name indicates. The 3D Contour toolpath is a common example of a Z slice toolpath and produces efficient and consistent finishes on steeper surfaces. Where Z slice toolpaths aren’t ideal is on shallow surfaces when the controlling stepdown produces a significant stepover. Surface stepover: Surface stepover strategies produce toolpaths that are evenly spaced from one another along the 3D surface to be machined, no matter the surface slope. 3D Scallop is a common surface stepover toolpath and is typically easy to apply to a variety of surfaces while producing consistent and predictable machined surfaces. I most commonly use surface stepover toolpaths when programming time is my highest priority, or when machin- ing segments of transitional geometry. While it may sound like surface stepover toolpaths are the ideal solution, they are often less efficient on steep surfaces than Z slice toolpaths. Surface stepover toolpath may also produce inefficient machine movement, including sharp direction changes as it follows the surface or boundary. Finally, sometimes the aesthetics of the toolpath don’t accentuate the part geometry and result in a less visually appealing surface finish. shallow, and transitional. Steep: I consider steep surfaces to be 45 degrees or steeper, plus or minus 10 degrees Shallow: I think of shallow surfaces as shallower than 30 degrees, but as steep as 45 degrees depending on how the toolpath moves over the surface Transitional: Transition surfaces are simply the surfaces that transition between steep and shallow surfaces. Know your toolpaths: Knowing your available toolpaths and how they are pro- duced will help you choose which toolpath – or toolpaths – best satisfy your priorities for each surface. 3D Contour and 3D Parallel are two examples of toolpaths that will produce significantly different surface finishes on the same surface slope. I generalize toolpath types into three categories: projec- tion, Z slice, and surface stepover. Projection: Projection toolpaths essentially take the sur- face to be machined, flatten it, apply a stepover toolpath on the flattened surface, and then project those toolpath lines onto the surface to be machined. The 3D Parallel toolpath is a common example of this type of toolpath. This toolpath works great on shallow surfaces and often does fine when driving straight up steeper surfaces. Projection toolpaths aren’t ideal when they side step up steeper surfaces where the controlling stepover could produce a significant step up, leaving large cusps and a poor surface finish. Bringing it all together: With all the possible options, 3D surface machining may seem like a daunting task. I’ve always found that break- ing each detail of this complex trade down into digestible components has helped me pull them all together to improve the productivity of my time in the shop and the quality of my parts. Learning containment techniques to apply multiple toolpath types to a single part with multiple surface types such that each toolpath is applied in an optimal way is critical to producing great results on all but the simplest parts. A classic example is using slope to contain a 3D Contour toolpath to only machine surfac- es from 35 to 90 degrees while containing a 3D Parallel toolpath to only machine surfaces from 0 to 40 degrees. This keeps each toolpath contained to geometry it can machine effectively while covering the entire part. With a good understanding of your priorities, the part geometry, and which toolpaths are best suited for differ- ent geometry, it’s not hard to efficiently produce quality surfaces that meet the part requirements. I hope this article helps you better assess your priorities, understand how part geometry affects different toolpaths and helps you choose what toolpaths are best suited for different geometry. Z slice: 3D Contour Combination: Parallel, 3D Contour, Scallop Surface stepover: Scallop