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Picking 3D milling geometries
I keep spending an extreme amount of time trying to pick geometries in 3D milling and I cannot figure out the supposed logic behind things.
Here we are undercutting by 0.2mm with a tool with 0.3mm relief.
What is logically missing for having Fusion understand that area I have picked in Avoid/Machine Surface is the surface I want the system to machine with a 3D contour tool path?
Ramp won't work as we need a horizontal first layer.
No matter what I have tried to pick as machining boundry the tool path comes up empty.
As I understand it the 3D machining should be smart and model aware, yet
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Would you be able to share your Fusion file here?
File > Export > Save to local folder, return to thread and attach the .f3d/.f3z file in your reply.

Seth Madore
Customer Advocacy Manager - Manufacturing
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Hi Seth, I have instead made this file that holds two of the challenges I cannot figure out in a smart way
The 3D contour should be able to mill this as 3D contour.
We don't have steep and shallow available
A slot like the one with the slitting saw we should be able to make with 3D Ramp or with 3D contour - Ramp we cannot get the top line straight and I cannot get the 3D contour to make a tool path. We end up making multiple 2D contours which seems like a stupid way
The protraction is a tool with 0.3mm relief cut that needs to mill a 0.2 mm undercut
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Personally speaking, I would favor the 2D Contour toolpath for undercuts that are in vertical sections, such as the post and the groove around the part. 3D Contour doesn't support Cutter Compensation, so you'd have no means of adjusting the size of the feature while machining it. Sure, you could add some negative stock to leave and then post the code out again, but that's really not a sustainable workflow to constantly be doing.
That said, by changing my selections a bit and defining things a bit differently, I was able to get both features to work with 3D Contour. Take a look at the second setup and compare it to the toolpaths you were trying to create.
Ramp is not capable of undercutting, it only looks at the surface, not undercut surfaces. I also tossed in two 2D Contour toolpaths that I would prefer to use ![]()

Seth Madore
Customer Advocacy Manager - Manufacturing
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Thanks Seth,
I'll study it further, but one thing that confuses me on both the tool 4 contours are the top heights
The flute length is 13mm yet the top height is roughly 4mm under the protrusion and 5.03 (8.03 under top) and I don't understand the logic that it is not 0 (3D logic takes care of it) or -13mm ie the whole flute clears
Fusion