This is a fairly simple instructable: if you can thread a needle (or have the tools to assist in doing so), you are probably qualified to make these. Before I begin, a little note on safety. When preparing the gear for use as a button (and when taking apart the clock to get the gear, but that's another story) wear safety goggles! Don't blame me if you ignore this advice! Also, if you are taking apart a clock to get the gears, you absolutely must be careful around the coiled springs. Those things are surprisingly powerful: I recommend at least a leather jacket, leather gloves, and a full-face shield! Of course, if you don't want to take the risk (or if you can't find a suitable clock to take apart: if it says "quartz," it probably won't work!), you can find gears on Etsy or Ebay, or anywhere else that sells steampunk art supplies. Also, mind your hands, as you will be working with a hand saw. I recommend a clamp, or a vise, so much so that you should buy one if you don't already have one available. I got a bench vise at an awesome local secondhand hardware store for $10, but if you can't find such a deal, Harbor Freight Tools sells them for $50 or $25 on sale, which is still worth it, so long as you have somewhere to mount it. I just used a piece of chipboard.
Anyways: here is a list of things you will need:
some kind of hand saw, that can cut metal (a dremel with a cut-off wheel works, too)
fabric garment on which to place the buttons
Anyway, let's begin.
The first picture shows the finished gears, ready to attach to the garment. To get to that point, you must first remove the shaft. Before that, you must put on your goggles, and place the gear in the vise, as shown. My gears had some odd Gatling-gun-shaped thingies (best way to describe them), so I removed these with a twist of the pliers. If you don't have goggles at this step, you may end up with a cylinder of metal hitting you in the eye, so keep that in mind!
After removing that, you want to saw off the long end of the gear shaft. once that is done, you simply use pliers to remove the other end. Note that I didn't remove anything in the pictures, because I already had all of the gears I need: I just wanted to show the steps.
The last picture is just to show off my $10 find. All it is missing is the bar for the part that turns to close and open the jaws, but I can just grab a suitable piece of metal, and place it through the hole to turn it.
Next, it is time to prepare the garment...