I didn't have any immediate plans to make one of my own, but when I found this beetle dead but intact on the side of the road, I knew it was time to try my hand.
Step 1: Materials
Clockwork pieces (you can get these really easily on Ebay)
Black fabric (to lay out gears on)
Step 2: Open Beetle
Lay out your work space: a work surface you can clean easily, ideally something disposable.
You'll need your scalpel, some tweezers, I used a pair of chopsticks occasionally.
Definitely prepare a cup of ethanol to sanitize things.
Hold beetle with tweezers where the thorax meets the abdomen. Carefully insert blade into the back end of the beetle. Work the abdomen apart from the wings. It will likely begin to pop! open.
You'll want to dip your beetle into the ethanol pretty regularly, if it's anything like mine. The alcohol will cut the smell. (Plus it gets bloody, and regular dipping helps wash the guts off.)
Step 3: Empty Beetle
Twist ties bend into a variety of shapes, and I found them quite helpful in scraping out the beetle's interior.
Get it as clean as possible; anything you don't scrape out will probably rot later.
Step 4: Assemble Gear Train
Put your gears together in a way that will (a) fit into the beetle and (b) look like a working gear train. Mesh some teeth together.
It would be awesome if you could actually make this beetle do something with the gears- actually, if you manage to make a working gear train that interacts with the beetle, I'll give you a three month Pro membership if you post an instructable on it.
But I'm not quite that ambitious.
Glue your gears into position with some silicone adhesive.