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This or That: Flowline Vs. HST Blend

This or That: Flowline Vs. HST Blend

By Callie Morgan and John Stauffer
Wednesday, January 26th, 2022, 9:00 AM PST

Which of these two Mastercam finishing toolpaths will give you the smoothest result? Well, it depends on the surfaces you are working with. Let’s compare the capabilities of each of these finishing toolpaths to help you decide which one will work best for your program.
Flowline Finishing Toolpath
The Flowline Finishing toolpath relies on the existing direction and orientation of the U and V curves on the surface of a part to create a smooth, flowing toolpath motion. When the UV curves in your surface are already set up in a way that matches the toolpath you envision, it makes applying this toolpath very simple. 

If the UV curves do not match the toolpath direction you’re looking for, you would need to use the Edit UV and Reflow UV tools in Mastercam to reorient the UV curves to match the toolpath direction you want. This is why adjusting the flowlines on the surfaces using the Edit UV and Reflow UV features, which were added in Mastercam 2021, are crucial to how smooth the Flowline toolpath is.

A complication can arise when you want to cut multiple faces with the same toolpath and the UV curves do not line up with each other. As you add more surfaces to this toolpath, it results in what we call “UV spaghetti'', making it increasingly difficult to manage and line up. However, the presence of multiple surfaces is where the Surface HST (High Speed Toolpath) Blend can really shine.
Surface HST Blend
The Surface HST Blend Toolpath does not rely on existing UV curves to determine the direction of the toolpath like Flowline. Instead, HST Blend uses at least 2 wireframe curves, or solid edges, to construct the basic shape of the toolpath cut motion. The control curves that are used to set the blend direction also do not have to be connected to the model itself, or follow its general shape. This allows HST Blend to have a greater degree of freedom when determining the cut pattern than Flowline. However, you may have to draw more additional geometry to get HST Blend to work. 

Additionally, the control curves that set the cut direction can even be used to create additional containment boundaries within the existing containment boundary (should you choose to use one). By placing the control curves inside of the part geometry, you prevent any toolpath motion from being created outside of the control curves.

Finally, HST Blend has both 2D and 3D projection modes. This means if you are working on a shallow surface, you can set the projection to 2D mode and get the best cycle times, while maintaining a good surface finish. On steeper walls, you can enable the 3D projection mode, which keeps the surface finish more consistent throughout the part’s surfaces.
So, which finishing option should you use?
These toolpaths have a similar finishing output but they are built very differently. It is important to note that if Flowline works well on a part, HST Blend can be used in its place just fine. However, this is not always true the other way around. 

Consider what types of surfaces you are working with to determine which toolpath will work best for your situation. The HST Blend toolpath relies on wireframe curves (or solid edges) to form the toolpath’s direction, whereas the Flowline toolpath’s form is limited to the UV curves of the surface.

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