It's my first take at making it through an online CAD software.
Step 1: Creating the Hammer Head
So change the workspace units to cm from inches, because metric is better. And select anyone of the sketch plans to start the work with, I selected top. After that pick the rectangle draw tool and make a 2X4 box. Once you have done making the box, use the extrusion tool to extrude the box to 2cm. At this point you will have a nice looking rectangular box. This will form the head of the hammer.
Step 2: Handle Time
After creating the base we start the work on the handle to wield it. The first step to that is selecting a parallel plane to the base and drawing a central line on the base, this will also serve as an axis to revolve it. After creating the axis, select the circle tool and start creating circles to the desired height. When you are done with that, erase one half of the circles from one side. Then select the revolve tool and click on the left-over circles, and the central line as the revolve axis. This step will give you the completed handle.
Step 3: Chamfer the Hammer Base.
Go back to the completed view and select the chamfer tool. After selecting it, start clicking on every single side of the hammer base, doing this will give the iconic Miljor look, and vola you are done creating Thor's Hammer.
Step 4: Thor's Hammer Mk1
This is more of a download the file and print it. I have used an online CAD medium, onshape.com; its free to use with one limitation only, you can only have 10 files at a time. The software is quite easy to get used to. So here is the first attempt of mine for replicating Thor's hammer. I will be trying a second iteration with more details, but since I have to rely on university's 3D printer, which has a really bad print resolution, it will be hard for me to print it and share the picture. If any of you does print it, especially with resin; please share a picture.
It literally took me 10 minutes to create the hammer. I'm hoping to use it as a paper weight, once it is printed with 100% fill. Cheers people. Have a good sunday. :)