Hi Morton,
OK.
As mentioned, what you are seeing is correct, as the helix will change tangency, in this case, due to the angular slope.
Although changing the tangency will give out an incorrect result, you can make slight changes to help.
After creating the helix with the helix tool(in this case 3 helix, the middle helix being tapered)
Zoom in to where the helix endpoints join
Trim off a small part of the end of each helix (you can use trim:- Add trim points). Here I have trimmed one helix endpoint and adding a trim point to the end of the other helix.
Then select those 2 helix and use "Blend" G1 to blend.
Repeat for the other joining helix endpoints, then join all those curves (helix + blends).
You can then sweep that resulting curve with your shape for the cutout.
In this example, this was the result.
- Steve
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