I made this thing for an engineering project. It took me like 2 weeks but that is because I am new to using inventor. It is of a gothic style and can be resized to fit on a necklace or chain. My teacher says I have to tell you all what I learned when making this. Most of what i learned had to do with the sketching, at first when I was starting this project I did not know i had to make different sketches for different features, so i didn't know I had to make a separate sketch for embossing, and that the sketch for embossing my lines had to be closed. And then I learned that you cant chamfer small features very well, so you have to adjust the size of your chamfer. I also leaned how to use the mirror tool and how to create a very symmetric design, while also keeping it interesting visually despite how symmetric it is. Making this should be easy for any experienced engineer or 3d model maker.

But for those of you who do not know exactly how to get started on making one of your own design, here is a step by step guide, it s not very in depth to leave room for creativity:
Step 1.) Start your sketch and select your YZ plane.
We are selecting this axis because it makes the most sense to me for it to be standing (up down) rather than laying (left right). But you could use your XZ plane if that makes more sense for you.
step 2.) Make your desired size and shape.
So for this part, your are gonna need to create a long rectangle, how long exactly is up to you and your use for this object, but I would say to make it at least 2-4 inches in length and around 1/2-1 full inch wide. It is important to remember that the size is completely up to you, and that sometimes 2 inches is not as much as it seems. I accidentally made mine too small and it was a bit disappointing. So make sure to use a ruler or another object for reference when deciding on your cross size.
Now that you have a long rectangle, you will make a rectangle across the middle or upper middle section of your first rectangle horizontally. It should have the basic shape of a sort of boxy cross. Very classic. Now add a line in the middle of your long rectangle, this will be your mirror line. Now you must dimension your sketch with the dimension feature.
Step 3.) Make it cooler. Add to that sketch.
Now you will add some details. Use your arch feature to add a sort of inward slope to the rectangles, so that they flare at the ends. You can also use your line feature to make the ends of your cross pointed, that would be pretty cool. To be sure that your design is symmetric, you can select the line you want to mirror using the mirror feature, and then select that middle line as your mirror line, now click apply. Trim any extra lines using the trim feature. Now you have a smooth and symmetric sketch.
Step 4.) Extrude.
Now that you have the basic outline that,( hopefully, isn't too boring), you can extrude, you will choose how far you want to extrude it, I would say around half an inch to a full inch, depending on how big you'd like it. If you want it to be very creative and detailed, make it bigger so that when we move on to step 5, you will have more room for designs. Now, assuming you know how to extrude, make sure when extruding your sketch that you choose to extrude your sketch symmetrically instead of the default. There isn't a reason for this, it just makes more sense to me.
Step 4.) Make another sketch.
Step 5.) Now to add more cool stuff.
Select project dimension and highlight the whole cross. Now hit offset and select the outline of the face of your cross. Now you can add whatever inside design you would like.
step 6.) Extrude
Now what were going to do is extrude our design, you can make the extrusion go inward or outward, that part is entirely up to you. Now repeat the same actions from steps 4 and 5 to ad another design within that first one. Or you can just add a new sketch and then use arch and line to add your designs within that extruded piece.
step 7.) Now you just chamfer your edges and add any finishing touches. For a double faced design you can use the mirror tool and mirror everything onto the back.