Self-Latching Trash Can Lock for Dogproofing

Yes, it's as fun as it looks!  Hidden magnets ensure reliable “docking” every time.  Even knowing they're there, though, the way it locks itself each time almost feels like a special effect.

Allows one-handed operation as shown in the video, or (at least with our can) you can also safely stand on the foot pedal and then hip-check or otherwise bump the lever and it'll pop open.

WHAT IT FITS: Designed for a metal can measuring 42mm OR LESS from the top of the lid to top of the metal body when a bag is fitted; cans measuring more than this will likely NOT WORK.  Should work on plastic bins as well, but not tested.

DISCLAIMER:  “Dogproofing” cannot be guaranteed with this design and probably depends on how mechanically inclined your dog is.  YOU are responsible for your pet's health.  The goals with this design are a) to be retrofittable and b) to eliminate the need for remembering to lock the can (e.g., so young kids don't have to be relied on to do it consistently…!)  (Also, unfortunately, it's probably VERY far from raccoon-proof.)

SETTINGS

I used PLA printed at 0.1mm Layer Height (but 0.2mm should be fine), 2mm walls, tops, and bottoms, and 30% infill. Supports required.

Two versions of the front piece are included – one that prints on its side to allow a slight can-hugging curve on the bottom face (but needs more supports), one that prints flat to be easier.

In theory, this could be scaled for other applications – to 120% and used with M6 hardware and 6mm rods, 80% for M4 and 4mm, or 60% for M3 and 3mm.  However, this hasn't been tested.

POSTPROCESSING

The hex holes in the parts are designed to hold the 5mm rods tightly (but obviously not so tightly that the rods would crack the parts).  The round holes should pivot freely on the rods. Cleanup with an undersized drill may be needed.

MATERIALS

• 2x 5x70mm Steel rods (must be a magnetic steel; may be as short as 60mm, but this may make assembly harder)
• 3x 5x1mm round neodymium magnets
• Superglue for the magnets
• 2x M5x20mm Button Head Screws - upper mount front pair
• 4x M5x16mm Button Head Screws  - upper mount back pair and front latch
• 6x M5 Nuts
• Optional: 6x M5 washers (probably a good idea for plastic bins)
• NOTE: you may need shorter screws, especially for the front latch, depending on how much clearance the bag needs.  Taping over the nuts and screw ends might be necessary to prevent snagged and torn bags.
• ALTERNATELY: good double-sided foam tape MIGHT work in place of the M5 hardware, but this isn't tested.

ASSEMBLY

1. Glue the magnets into the front latch, in the center pocket between the screw holes.
2. Pin the lever to the upper mount with one of the rods, ensuring it hangs and swings freely. You may need to hammer the pin through.  TIP: Chucking the rod in your drill and spinning it while pushing it into the hole can help get it through the tight parts!
3. Insert the second rod in the lower holes of the lever (the drill trick makes this a lot easier).
4. Test the assembly carefully on your can to determine where the pieces should go.  The lever must be positioned so it can hang vertically, but not so far that it could swing inward enough to catch on the can when the lid closes.  There should also be a small (~1mm) gap between the bottom rod and the “hook” surface to ensure the lever can swing into place – aim for the place where the magnets naturally hold it.
5. TIP: if the bag sticks out of the top of the can too much, it might interfere with the lever's motion.  Make sure there's enough space!
6. When you are satisfied with the positions, mark the fastener locations through the holes with a pencil.  Drill the holes a bit oversize to allow some adjustment.  BE CAREFUL – holes in sheet metal can make sharp edges!
7. Mount with the M5 hardware.  Done!
8. Marvel at the magic or adjust until it works, and then marvel!

TROUBLESHOOTING

1. If you goof the locations slightly and the lower rod can't swing under the hooks or hangs too low for the magnets to grab, the height of the lever can be adjusted after mounting by carefully bending the can lid metal to tilt the upper mount up or down.
2. You can also adjust the locations by drilling the holes a bit bigger.
3. If the lever doesn't reliably get grabbed by the magnets when it's hanging at its natural / neutral position, make sure it pivots freely (drill the round holes bigger if needed), OR you may need to add some washers or other material between the can and the front latch to shift it forward.