I tried AI STL Generator when I needed a custom part for my home printer and did not want to learn complex modeling software. You type what you want in plain words or drop in a picture, and it builds a print-ready STL file for you in less than a minute. I like that it also has a built in viewer and simple editing tools, so small fixes take seconds. It works well with common slicers and popular printer brands. The free plan is generous enough to test a few ideas before paying anything.