Does anyone have any good examples of spring latch designs? I’m planning on designing some boxes and inserts for board games, and having ways to latch these boxes using as little space as possible would be amazing.
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I do a lot of latches using neodymium magnets instead of spring latches. They’re cheap, small, can be tucked away under a fascia and not show and there’s something cool about a magnetic only latch 
The spring ones tend to be bulky so need a bit of design done to hide the components - more than neo magnets anyway.
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I haven’t actually used them in anything yet, but I got a box of tiny magnets on Amazon for this purpose. I’ll be curious to see what others are doing, though.
Not a spring latch, but this box stays closed really well, although I do put a rubber band on it for traveling for safety’s sake. The lid is made in two parts, one matching the outer size of the box below, and the other matching the inner, so it seats into the hole with a tight tolerance. I used the inner layer to position the sides to be glued, “clamping” the whole thing with a couple of rubber bands. Then I glued the inner layer to the outer (which I had to do twice because it came apart the first time - used a better glue and more of it the second time).
I think part of the reason it stays closed as well as it does is because I made the box pretty tight to the components - there is very little wiggle room.
I’ll be curious to see what others say.
I used the little neodymium magnets for these cases as well - they do tend to stay closed until they are separated.
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I have several designs but they are all 3D printed with a strong PETG or polycarbonate material. I tend to customize them for whatever project I am working on at the time.
I have a box that I keep carving tools in that small bottles of gray goose vodka came in that slides in and out and had a nail like pin that kept the slide closed till it was sold. I have not used the concept yet but am thinking it is a good way to go.
The problem with magnets is that they’re not “positive locking” like a mechanical latch. Magnets are great for holding stuff on provided it’s not subject to high mechanical shock (like dropping it on the ground). I use them to keep parts attached to my model airplanes, like hatches and “ordinance” for the scale models. They stay in place no matter the aerodynamic forces, but I’ve had some pop off on hard landings. So if you want a lid that’ll stay closed in a hurricane, magnets are fine. If you want it to stay closed if someone drops it on the floor or kicks it down the stairs, you want something mechanical.
What about something like the snap-head fingers used for self-locking finger-joint boxes? You’d need an extra bit for a catch, but otherwise it should work.
I need something that will keep the lid on as it is jostled in my car, so a magnetic latch should work just fine.
I’m thinking of getting a block of 1/8" cube magnets, so that I can cut a quick 1/8" hole in the edges of my box and my lid and epoxy glue some magnets in that will snap together
Get some 1 mm thick neo magnets. You can deep engrave a hole for them very easily and just glue them in with epoxy. (Make your hole 1 mm larger in diameter than the size of the magnets though to account for fit. Deep engraved holes have a slope inside unless you ream them out.) 
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Should both sides of the latch have a magnet, or should I use a tack or some other piece of metal?
You put a magnet on both sides. (And be careful of the orientation when you glue them in, they will attract in one direction and repel in the other. AMHIK.) 
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good news on the whole “Messing up magnet orientation” is you could form a short spring effect so that two of your pieces never try to touch each other.
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Yeah, I was actually shooting for having them repel each other on the initial carousel design, to reduce friction and increase spin. Got one in there backwards. 
I made a few acrylic boxes with snap/spring catches. It has been a while but the design in shown here actually worked quite well. Beta day - three (Acrylic Boxes and iPhone Tripod)
Tip on installing the magnets - put a piece of wax paper or even packing tape between them, a dab of epoxy in each recess, then close the box with them in place. When the epoxy cures, they will be perfectly aligned…
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