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.
Step 1: First, You Must Prepare the Gears
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...
Step 2: Removing Buttons and Sizing the Holes
In this step, the first thing you do is remove the buttons from the garment (unless there aren't any buttons in the parts where you are going to place the new ones). I don't know what kind of buttons your garment has, but mine was a denim jacket from about 1969, so the buttons were riveted in. I just pulled them out with pliers.
Next, you should see if the gears fit the buttonholes. If the buttonholes are too small, you will need to cut them larger. If they are too big, or if you cut them, you should probably sew the rims of the buttonholes. There are other instructables for that: I'm sure you can find them. Tell me in the comments section if you can't.
Now that that's out of the way, it is time to sew on the buttons
Step 3: Sewing on the Buttons (or "Just Sew Some Gears on It and Call It Steampunk")
Now, it's time for the main attraction. First, of course, you must cut some thread, and thread the needle. The amount of thread depends on a bunch of variables, so it is best to cut more than you think you will need. After the needle is threaded, you want to make it a double thread, and tie a knot at the end. To do this, you must pull both ends of the thread, until the ends are at the same point, and the needle is at the opposite end of these. Then, you tie a knot in the end by wrapping the end around your pointer finger, then pulling it back with your thumb, twisting it. Finally, you tighten the knot with your thumbnail.
Now that your needle is threaded, you want to put the needle through the place where you want the button, starting on the inside. Then, you pull it through the space in the gear between spokes, as shown in the third picture. After that, you take the needle over the spoke, and put in back into the fabric right next to the spoke. Now, you will want to put the thread back up through the fabric, right next to the next spoke. Keep going around the spokes, and when you have gone around the whole gear twice, you want to put the needle through the fabric, towards the gear, but not through the gear. Instead, you want to wrap the thread around the thread that is in between the gear and the fabric, while being careful not to get the thread caught on the gear. Wrap it 4 times, then go back into the fabric.Finally, you want to sew a stitch 3 times in the same place, and then cut the thread, and tie a knot to fully secure it. cut any thread that hangs past this knot, and now you have one button. Continue all of these steps for each button you want to replace. The last two pictures show how this looks.