I redesigned my cart joint to include a latch, as I found the old method too cumbersome.
Wheels for this cart can be found here: https://www.thingiverse.com/thing:3996387

You will need the following for this project:
A cart of some sort. I used this one:
https://www.walmart.ca/en/ip/mainstays-deluxe-shopping-cart/6000195942919
6 x ¼” x 1-½” bolts with matching nuts (0.495”)
Hacksaw
Pencil
Tape
¼” drill bit for steel, drill
-Also some sort of Velcro/sewing thread/needle is also recommended if you wish to use the bottom belt on the bag (useful for securing the folded up bag to the cart as well).

I bought a cart from Walmart, but it was a bit too big to stealthily take to places before use, so I decided to cut it in half. Added an over-engineered, 100% infill hinge so it didn't look weird. Fits in a large fabric grocery bag now.

-Tips for use:
Use the ‘cart test slide on 1.stl’ and ‘cart test slide on 2.stl’ to make sure that it will fit before printing the whole thing. There is a small gap between the part and the joint stl’s so you can use tape to create a friction fit.

Measure out the height of the cart from top of handle to bottom of wheel and divide by two mark the tube on both sides. Cut tubes at the mark with a hacksaw and debur.

After printing out the joints, use tape on the tube between the tube and the joint to ensure a snug fit. Place one of the joints halves on the tube, ensuring that the larger hole is on the front side of the cart, and drill out the bolt hole in the tube on one side, using the joint’s hole as a guide. Use a bolt to keep the joint half in place, then drill out the other side from the opposite side. Don’t try to drill through both sides of the tube in one go.

You can use elastics to keep the latch in position using the provided holes.

If you like the design please consider tipping me or donating at:
paypal.me/ShrinkRayme
Thanks!