CNC West Feb March 2019

62 www.CNC-West.com CNC WEST February/March 2019 CAD/CAM/CNC Perspective By: Tim Paul Tim.Paul@Autodesk.com Instagram: OneEarTim The perfect 3D Surfacing toolpath... part that meets the print,” is the perfect reminder of what we should all be focused on: efficiently producing parts that meet the requirements. Applying the appropriate combination of toolpaths is an important part of running a profitable shop. Know your geometry: Knowing your geometry and how toolpaths move along the geometry is one of the most important steps in ma- chining quality 3D surfaces. Steep and shallow surface geometry are two examples of surfaces that require dif- ferent toolpath strategies to produce similar surface finish results. I generalize surfaces into three main categories: steep, The last issue launched a series exploring the details of 3D machining toolpaths. In that issue, I covered some of the fundamentals that changed my 3D machining game, including tessellated surfaces, boundary conditions, and the effects of smoothing on point distribution. In this issue we will continue the 3D toolpath discussion. So, what is the perfect 3D toolpath? The most generalized answer is something like, “the most efficient toolpath that produces a surface that matches your design intent.” In other words, there isn’t a perfect 3D toolpath. If there was a single perfect toolpath, we would only have one 3D surfacing toolpath instead of the many that are available. The real answer is that you need to decide which toolpath best matches your priorities. In this article we will explore different priorities to consider and how different toolpaths satisfy different priorities. Know your priorities: Defining your priorities is an important first step before starting to work through different toolpaths for different geometry types. This reminds me of the funny sign I grew up seeing in my local engine machine shop, “You can have it done right, cheap, or quick. Pick two.” It’s a good reminder that everything we do in life and in the shop is a compromise of many different things. I generalize my priorities into three categories: time, mea- surable surface finish, and surface appearance. Time: Time is easy to define and measure, but there are many tasks that consume time in a machine shop. I usu- ally focus on measuring and minimizing CAM program- ming time, machining time, and setup/edit/change time. Which toolpaths you choose for different surface geome- try will have a significant impact on the time required for each task. Some toolpaths are very efficient to apply on the CAM side but may take significantly longer machine time to achieve the desired surface. Other toolpaths may take more upfront work on the CAM side and be more efficient in the machine but take extra setup/edit/change time to get the desired surface result. Measurable surface finish: The measurable surface finish is typically driven by engineering requirements from the customer or based on the application of the part. When the measurable surface finish requirement is out of my control, I compromise programming time and machining time to achieve the required surface finish as quickly as possible for the entire job. I may prioritize a quick to apply toolpath for a job of one part – even if it’s less efficient in the machine – to minimize the total time to delivery. On the other hand, for a large job where I’m trying to minimize cycle time to have the shortest total job time, I may prioritize a toolpath that is more efficient in the machine but takes some extra time to apply in the CAM and may require some additional adjustments. Surface appearance: Surface appearance is generally a matter of visual opinion. A combination of details such as how a part captures light, how visible the toolpaths are, and how the toolpaths flow with the part geometry all af- fect people’s opinions of the visual quality of a part. This is the category I find myself and many other programmers spending an unjustifiable amount of time on. I used to Projection: Parallel spend unreasonable amounts of time making aerospace parts look like beautiful works of art suitable for the picki- est consumers only to find out that they were getting bead blasted and painted in thick baby food colored paint . I enjoy making pretty parts as much (or more) than any- one, but a business owner and programmer’s job is to run a profitable business. Your goal should be to produce parts that meet the requirements as efficiently as possi- ble. Old Man Frank’s saying, “the only perfect part is the