What follows is the 'right way' to make Steampunk goggles. I am showing off the basic method and not walking through the build of a finished set of goggles. When you get to the end of this instructable you will still have a bit of design work and construction to do. But you will have the skills to do them.
This is the method (more or less) employed by the magnificent Gogglerman in many of his designs. In some areas this method is even an improvement. I do not pretend that my finished product is anywhere near the same league as Gogglerman. The man is a true artist; a savant even in the way he solves design problems.
But where the master shows off his work he does not like to spend time explaining his process. Many who comment on Gogglerman's work complain (rather aggressively) that he does not give step by step instructions on how to make what he's showing. I intend, only, to fill that void.
This is my first instructable, so constructive criticism is, of course, welcome.
Keep in mind please, I am an artificer not an artist. The techniques I describe can be used with greater skill and creativity than I possess to create works of art. They are employed by myself only to solve a problem and the final product is often aesthetically inelegant.
Step 1: Design
We need to know what shape to cut our sheet metal.
In this example I'm making goggles that are about 2inches in diameter. It's not all that important (to me) if that number is a little off, so long as both eye-cups are the same dimension. If you demand precision, it is a simple matter of taking much more time with your mensuration.
The diameter * PI = the circumference as well as the nominal width of our template. the 'length' of the eye-cup will be about 3 inches which is also the height our template must be. For reasons I will describe later, I add about an eighth of an inch to each side of the pattern,
To conform to our face the goggle eye-cup will need to be shorter at the bridge of the nose than it is near the temple.
To do this center a ruler horizontally against the bridge of your nose, centered vertically on the pupil of each eye.
Take a rounded straight object like a pencil (eraser end) and hold it against the face about an inch from your pupil. This is the point on the temple side. Mark the distance between the face and your ruler at this point and measure it.
Draw a line on a piece of paper the same length as the eye-cup circumference, in this case about 6.3 inches. At each end draw a perpendicular line up the page the length of the measurement we took earlier.
Mark the halfway point on the horizontal line and then draw a nice sine connecting the top of the 2 vertical lines. You can get fancy and measure the contour of your face perfectly but it's not really needed.
Now extend each of those vertical lines below the horizontal line by the 'extra' length you want for your eye-cups. By extra I mean the part that extends past the bridge of your nose. My pattern added about a half inch for this.
Add an eighth of an inch to each side and cut it out.
What we have now is a sheet metal pattern for the eye-cups that puts the seam on the outer extreme of the goggles, nearest the temple. For aesthetic reasons or a host of other kinds of reasons you may wish the joint to be somewhere else. To do this, cut the pattern where you would prefer the seam and join the two longest edges. Do this before you add the two eighth inch bits to the edges of the pattern.