Step 5: Make it Comfortable
I got the idea to add some form-fitting support from aintMichael's Steampunk Airship Goggles.
In step 3 of his instructable, you can see how to construct the eye-cup that I used in my goggles.
In this case, cut out a pentagonal piece of leather, like the one in the picture below, so that the width is just a bit longer than the circumference of the frame ring, height is between 1/4" and 1/2". The angle of the taper on the last two sides is up to you. Try fitting it to your face when you're making your own.