Milk Bottle Locking Cap "Milkey"

by peaberry Oct 15, 2017
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I made this today but the mechanism can be pulled clean off the cap. I used uhu superglue. Does anyone have any recommendations for a better glue?

I think mine stuck really well just using superglue, but it could have been some clear adhesive for plastic (can't remember for sure). I did take care to make sure the parts were clean and dry, and at room temperature before gluing though.

First I would make sure all the components are left to get to room temperature. Make sure the plastic is clean (could maybe use some alcohol as a degreaser?). You could look up the plastic type (if it has a recycling symbol) and look up which glues are recommended for that type of plastic. The cap might be HDPE. You could try to roughen the surface with sandpaper then vacuum to remove any dust before applying adhesive.

Another more extreme option of course would be to use a stainless steel washer and stainless steel screw straight through the cap!

Done! I'm ready to roll and have my milk last more than a day! thanks.

Great - good luck!

I checked out one of my milk bottles last night, and it has the plastic type 2 symbol for recycling, which is HDPE.
Reading through this article, it does sound tricky to bond:
That said, mine seems to be stuck on there pretty securely, so it's not impossible.

Thanks a lot for your design, I made a remix of it to fit onto a tetra pak:

Milk Bottle Lock for Tetra Pak
by G0dl1ke

Thanks, I like your remix, it looks great ;)

Where did you get the 3mm by 18mm metal shafts from ?.

I had a pack of 3mm x 75mm steel shafts, which I cut down to size. I think these are the ones I used:
You can find similar on eBay, Amazon, Banggood (all the usual suspects!)
However, there are a few other options you might have lying around. You can often salvage metal shafts out of old CD drives and computer scrap, or you may be able to find a round nail with the right diameter and cut it down.
Hope this helps!

Brilliant. thanks. will let you know how it goes.. building one for a mate. whos milk at work always gets drunk !..

Great - hope it saves his milk! Would be great to see another "make" if you get chance ;)

Hi. ive made a plastic key for this that seems to be pretty study if your interested.
(so you dont need the metal pins for the key).

Many thanks

Thanks, interesting! It did cross my mind to try this, but I wasn't sure it would be strong enough. However, I guess if you print the "pins" flat to the bed as in your design above, it would be pretty sturdy. Thanks for sharing.

Just an update . It seems the feeble plastic milk carton is no match for a determined milk thief.. just found the milk in the fridge with the milk lock placed on the top.. i.e someone just ripped the whole thing off and drank the milk.. it's not broken , but it's made the plastic thread on the milk bottle weak. Need to find something a bit harder to break into. :(

Wow! that's some extreme milk theft.. amazing that people will go so far to steal your milk :(
We are in a fairly polite office environment so it works for us, but I think this design will only discourage casual theft!
You could make something more substantial with a base plate that sits under the bottle, and cables from the base plate to retain the cap, or decant the milk into a more substantial bottle (threaded glass bottle, stainless steel or thermos flask?)