Using screw modifier produces weird surface overlaps

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My screw modifier is not producing the same results as in the lesson. Seems like using the modifier generates additional phantom geometry. Here are a few images to illustrate the problem. I turned on face orientation as I suspected there was a problem there. Without the modifier, everything seems okay. With the screw modifier, it seems to flip the normals but I’m not sure how. Normals direction is outward so I’m not sure what other setting I may have missed.

By the way, no amount of fiddling with the steps make a difference. To be clear, there is only one object in the scene. The last two images are with Steps reduced to only 6 to show that weird geometry (very last pic is the render).

Screw-modifier-04
Screw-modifier-042552×1292 262 KB

Screw-modifier-01
Screw-modifier-012548×1291 365 KB

Screw-modifier-02
Screw-modifier-022545×1281 403 KB

Screw-modifier-03
Screw-modifier-032535×1277 279 KB

Screw-modifier-05
Screw-modifier-052537×1275 358 KB

Screw-modifier-06
Screw-modifier-061920×1080 156 KB

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It is because you are ‘screwing’ a 3d object. Delete half the cube, leaving one side, a profile shape effectively. As you are doing it, Blender is rotating eight points and their connections each round and up when up is added, that is not a profile so they do it all on top of each other as they all go round. Hard to explain. See Images.

screenShotScrewMod1
screenShotScrewMod13782×1963 544 KB
screenShotScrewMod2
screenShotScrewMod23782×1963 577 KB

If you want to duplicate rotate, even upwards as well, use the array modifier, utilising an empty to do the rotational bit.

screenShotArrayWithEmptyForRadial
screenShotArrayWithEmptyForRadial3782×1963 532 KB
a 3d object on a spiral, use the array modifier.

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This definitely makes more sense. You’ve saved my head from many bumps against my desk!

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