Escutcheon surround

Next we work out the length of the template for the leather surround, to do this, measure the diameter (distance from one side to the other) of the escutcheon, then multiply by 3.2 (this is slightly larger than pi on purpose), this is the length of the template.
On a piece of paper, draw a line of that length, then draw lines of about 20mm at right angles to each end of that line. Now draw a curve joining these two lines. As I think I'm doing a really bad job of describing this bit, take a look at the image below, or better still, download it - if you set the size correctly you can print this out and use it as a template. Once you've got your template drawn/printed on paper, use a stanley knife or scissors to cut it out.

For the leather surround pieces I bought an old belt from a charity shop, ensuring the belt was wide enough to fit the template on.
Place the template on the belt - for this prototype I used the end with holes in to give me a couple of practice runs before using the untouched leather further along.
Draw around the template, holding it in place and making sure it doesn't move around or bend while you do so, then remove the template.
Using a stanley knife extended a couple of centimeters, score along the lines you've just drawn on the leather (be sure to do this on an old wooden board or something, not on a thin layer of cardboard on the dining table). Once you've scored the lines the knife will more easily follow them when you cut along them again.
For the next part I retracted the blade to a couple of millimeters, which meant I could put a lot of pressure on it to cut through the tough leather without snapping the blade. I then repeatedly cut along the lines until I got all the way through (this took quite a while and some parts were tougher than others).
It should go without saying, but when you're cutting with the stanley knife, keep your fingers away from the direction the blade is cutting

Now you can insert the leather into the escutcheon, straight edge first. If you've allowed enough extra length on the template it should overlap by a few millimeters - this is fine, you can always remove a bit, but you can never add back on.
Making sure the leather is pressed against the side all of the way around the escutcheon, if they do overlap as in the photo above, mark one of the ends where it meets the other. Cut off the overlap from this one end (be sure not to cut that amount off both ends!). Now when you insert it into the escutcheon it should fit as in the image below, requiring a little pushing to get the ends to meet snugly but firmly. I found that with the thick, stiff leather I was using this was tight enough to hold it in the escutcheon so I could pick it up without it falling apart - if you use a softer or thinner leather you'll need to find some way to get it to stay in, either with sticky tape or by some other means.

Now you can hold it up to your eye and look in the mirror. You may find that due to differences in face shape that you need to trim a bit off here and there to make it fit - now is the time to do it.
Once that's done, you need to mark on the leather where to put the holes for the nose piece and for the 'strap' that will hold the goggles on your face. To avoid confusion, be aware that the two holes in the middle of the example above were already there from it being a belt!
If you imagine a horizontal line across the centre of the goggle, the strap hole should be a little up from that, somewhere between a quarter and half way to the top. I put the hole about 5mm in from the back edge of the goggles, which was appropriate to avoid tear of the leather I was using, and far enough back to avoid twist (if you put it too far forwards it may pull the goggles out to the side).
It's best to create the second goggle before marking the position of the hole for the nose piece. Be sure to make the second goggle symmetrical to the first, so you should turn the template over and use the other side from the one you used for the first goggle.
Hold the two goggles up to your eyes and look in the mirror, you should mark on the leather where the goggles meet the bridge of your nose (the bit where glasses would sit). You can make holes in the leather using a bradawl (I think that's how you spell it), which is basically a tool something like a screwdriver but with a sharp pointy bit instead of a flat edge. Don't make the holes too wide, you want it to be a reasonably tight fit for the chain...

Now you have the holes, you can feed the chain through. The chain I used was from B&Q, 3mm brass plated. Because of the tight fit of the hole, the chain was able to remain fixed in the hole without any additional sticking or fixings, you only need a few links through for the straps. I found I could push through one link with my thumb, and then use pliers to get hold of that and pull through more. The nose piece is a little more tricky, as you need the goggles close together and it can get fiddly, however once it's through you can adjust the length of the nose piece by just pulling links through on each side. I was surprised by how much difference shortening the piece made to how well the goggles fit - when the chain was a little longer the entire assembly was twisting and the nose piece was half way down my nose, which wasn't comfortable and twisted the straps too.

This is one goggle assembled, with chain, which might show you some detail that otherwise isn't obvious on the completed goggles.

The Lenses

First ensuring the lenses would fill the lens hole in the goggles, I bought some really cheap glasses with plastic lenses, then managed to remove the metal frame by soaking in hot water and using brute force to twist them off.
The lenses were too large to fit inside the goggles, so (with them being plastic) I filed them down to fit inside the leather eye-pieces.
As a final touch, I stapled the ends of the leather eye-pieces together to stop them coming apart.

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The Lenses

First ensuring the lenses would fill the lens hole in the goggles, I bought some really cheap glasses with plastic lenses, then managed to remove the metal frame by soaking in hot water and using brute force to twist them off.
The lenses were too large to fit inside the goggles, so (with them being plastic) I filed them down to fit inside the leather eye-pieces.
As a final touch, I stapled the ends of the leather eye-pieces tog

The completed goggles!