It seems like every year I tell myself I'm going to make something for my wife for Valentine's day, and every year I run out of time and my plans fall flat. Well this year it looks like my plans might actually come through. I had the idea on the way home from work last night and started on it after the kids went to bed. This will be a little heart shaped locket, but instead of the usual precious metals it will be made from mostly tool steel and a tiny amount of brass. To make this a simpler project than it otherwise might have been, I decided no hinges. The two halves would separate completely after being unlocked. I decided to use 3 steady pins - 2 to locate the plates to one another, and the 3rd to fit into an eccentric cam housed in the opposite plate. When the cam is turned (by a key, or a small screwdriver), it will bind against the mating pin. With the other 2 steady pins being a perfect fit, that will keep both halves locked together. It was a simple enough design so I felt I had a shot at getting it done (or at least presentable) in the two evenings I had left to do it (including tonight).
I started with just some rough sketches to help get the design worked out in my head, and to help come up with a plan for the order in which to make the parts and perform the various operations.
For material, I started with some flat ground O1 tool steel for the plates, that I sawed off from leftover scrap I had from another project:
I covered one plate in blue permanent marker and then used a small pair of dividers, machinist's rule, and scribe, to lay out heart shape and the locations for the steady pins:
With the two plates clamped together, I used my small benchtop drill press to drill the holes for the steady pins:
Then turned 3 steady pins from brass (when making steady pins, a slight taper must be applied for a proper fit) and drove them into place in one of the plates:
On the opposite plate, one of the mating steady pin holes needed to be turned into a counterbored recess where the little eccentric cam piece would fit. Every time I make a counterboring drill bit for some purpose, I bag it up and store it away for future use, and I was able to find one I made previously that was a good size for this. Here is the mating plate, with the counterbore formed for the eccentric cam:
Then I chucked a piece of W1 drill rod into the jeweler's lathe and turned the blank that would become the eccentric cam lock. I left the overall length, and the length of the shoulder in the middle, oversized:
Now I needed to drill a hole part way through it, that was off center. I chucked the part back into the lathe, with a piece of 0.007" diameter spring wire between the part and the collet on one side (making it 0.007" off center). I started by using a small center drill to start a pilot hole:
Then I followed with a 0.059" diameter machine length drill (machine length drills are nice and short, which is usually ideal):
I then turned the length down until it was a perfect fit in the plate:
The head of the locking cam, that sticks through the plate, needed to be slotted (so a tiny screwdriver or key could be used to lock and unlock it) and in this case the easiest way was to use a jeweler's saw (carefully!). If I had been thinking, I would have done the slotting before reducing the length of the part, which would have let me perform the slotting using a slitting saw in the milling machine. Here's the head of the locking cam, after slotting - crude, but effective:
Next, I needed the mating brass pin for the cam lock to be a little smaller in diameter, and slightly off center. I carefully filed it down by hand until I had a nice fit and a good locking action. Here are a couple of pictures of the two plates locked together using the cam lock, from each side:
By this time, it was quarter past 3 in the morning and my eyes were starting to burn so I called it a night. It'll be another late one tonight, but I think I can get it presentable in time for V-day. I need to mill a shallow recess in one plate, to hold a tiny photo or whatever, make a little retaining screw to hold the cam lock piece in place when the locket is open, then saw and file to the heart shape scribed onto that one plate, bevel and polish it, then heat treat it to a nice purple color and clear coat it to prevent rust and keep the color from wearing off. Not sure exactly what I'll do to allow mounting a jump ring (so it can actually be worn) - probably just drill it, but we'll see.