Taking control of advanced 3D-toolpaths (tolerance issue)

[Anonymous]

Dear community,

I am trying to mill a challenging contour into a injection moulded part. My goal is to mill the contour of the part in one go, no tool change and ideally no unnecessary tool travel whatsoever. The contour is 3D, and I want to mill along a path with continuously changing z-heights, which makes 2D-/3D-contour operations unattractive options. By far the best I have come up with is the Pencil operation. However, I find myself unable to control the toolpath to my liking, especially at the end of the arch the tool exits the toolpath at an angle and threatens to scratch the surface of my part. Since it is a injection moulded part and therefore fairly geometrically inaccurate, I can't say for sure that this is an area where the endmill will have free space to travel safely without crashing against the part and scratching the surface when exiting. Also, I find that the tool is unnecessarily traveling too much between some end points, and I'd prefer the tool to exit at the same spot it entered.

Interestingly, the toolpaths seem to get better the higher the tolerance levels. The toolpath with 0.2 mm tolerance is exactly the toolpath I'd want for a 0.01 mm tolerance operation in terms of entering/exiting (same point) and no unnecessary travel. This kind of confused my understanding of tolerances, as I can't seem to understand why high/low tolerance (so to say the resolution of the curve) does have such a big effect on the "quality" of the toolpath. I could always use a smaller endmill (0.8 mm currently), or increase the width of the contour (1.10 mm width currently), but I kind of expected the 0.8 mm endmill to handle a 1.10 mm wide contour. I know that I have to have enough space for the endmill for different tolerances to add up and still generate a good toolpath. But I don't understand why high tolerance makes for more intelligent toolpaths. The high tolerance makes the toolpath edgier, and since this will eventually be a surface exposed to the user, I'd definitely prefer a smoother contour. If there are better approaches than the Pencil operations, I am open to proposals.

I attached the part and a screencast. I selected the same contour and chose the same 0.8 mm flat endmill for all three Pencil operations. They only differ in their level of tolerance (0.01 mm; 0.1 mm ; 0.2 mm).

Thanks for your input in advance.

[Anonymous]

I am still struggling to come up with a proper solution to this problem. I feel like I backed myself into a corner with this Pencil operation as every checkbox/option I manipulate makes things even worse. Maybe an entirely different approach/operation would yield better results?

Any help is much appreciated. Thank you.

Dominik

[Steinwerks · Accepted solution]

I think Trace (actually under 2D operations) might actually be your best bet here, although it may need some tweaking on Axial Offset, and perhaps some Axial Offset Passes. Is this geometry as modeled, as in that is a slot into a hollow area of the part?

[Anonymous]

Hey Neal,

Trace looks very promising indeed. As you probably may have guessed correctly, the part does not have that hollow cavity in reality, it is just a means to control the cutting depth of the pencil operation. If it wasn't for that, pencil would cut right down to the bottom of the part.

I find it very interesting how often 2D milling operations are the way to go as opposed to 3D. For sure I would've bet a 3D operation should've been the way to go ... but trace looks so much simpler and more appropriate.

I am still a bit bewildered of how tolerance works for pencil, it is the opposite of what I would have expected.

Thank you very much Neal for looking into the part itself.

Dominik