The point in 2D Sketch3 is the point where the attached line is tangent to the projected geometry. This should be the (projected) point where the cutter starts to remove material as it move along the helix. The attached line is parallel to the other construction line in the sketch, which is perpendicular to the projected line representing the plane normal to the end of the helix.
This projected point, along with the Y axis defines the plane that cuts the tool at its maximum boundary when looking normal to the end of the helix. On further thought I'm not sure that this is exact. The projected geometry in the 2D Sketch3 might need to be unfolded onto the sketch rather than projected at 90 deg to give a more precise solution. In addition, creating two guide helices at either end of the profile might help with accuracy.
It did take a couple of kicks at it, Inventor was (as it can be) eager to report profile and intersecting geometry issues where none was apparent.
I stumbled about this thread today for the first time, but I'd like to add some comments.
I've seen every sample here, but all of WHunter's inputs show small collisions being left between cylinder and screw. The same can be said about Neil Munro's approach. I've played with some similar profile contours near Neil's profile, but none of them could be swept without collision.
I've played for myself with this stuff before, even with progressive screws (See STEP-file, I didn't find the original Inventor parts). I used the same method as Sam_M, and IMO that's the best one for Inventor users.
Why is it best? Look at my sample (just a refinement of SAM_M's file). The key is the contact line between screw and cylinder. It's an S-shaped 3D curve.
If this 3D profile curve could be swept along the helix, than it would be perfect. But as it is now, Inventor only can sweep 2-dimensional profiles. Thus, a boolean operation of cylinder arrays along helix is best.
If you're comparing the imported SWX screw, you can see a similar contact zone between screw and cylinder.
NMUNRO, I LIKE THE WAY YOU THINK.
I HAVE DONE SOMETHING SIMILAR A LONG TIME AGO, AND I CAN GIVE YOU CONGRATULATIONS BECAUSE YOU ARE UNDERSTANDING THE WAY OF DO IT WELL.
YOU HAS GIVEN THE FIRST STEP TO DO A FEED SCREW, FOR CIRCULAR BOTTLES FOR A NON VARIABLE PITCH HELIX. IF YOU TRY IT A LITTLE BIT HARD, YOU WILL GET IN A SHORT TIME THE WAY TO DO IT FOR A VARIABLE PITCH AND FOR IREGULAR SHAPES.
AND I CAN CONSIDER THAT THE BEST WAY AND EXACT WAY OF DOING IT IS WITH A RECTANGULAR ARRAY. AND AFTER EXPORT IT TO A STL FILE.
SOME CAM SOFTWARES CAN IMPORT STL FILES, AND CAN SMOOTH ALL SURFACE, SO WHEN PIECE IS MACHINED WE CAN OBTAIN VERY GOOD RESULTS.
THERE ARE A LOT OF WAYS TO ACHIEVE THE SAME RESULT.
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