Tips for STL Import?

Hello all,

I've been struggling with the import of a simple coil. Was wondering if anyone had any tips for how to build an STL file for the best success. I've attached a few images, no matter what combination of Normal/Surface deviation I use, I can't seem to get a clean import.

Any help is greatly appreciated. I am aware there is a CAD module, but it is out of our budget at the moment, so I am stuck with trying to get STL to play nice.

Thanks!