Trunk Bag Hooks

I got tired of my grocery bags always falling over on the way home, so I poked around in the trunk and found some holes (vents, maybe?) in the "roof" of the trunk area I ought to be able to mount something to:

There are a series of these holes near the edge of the top of the trunk.

With various measurements, test prints, and the use of a contour gauge to pick off the shape of the metal around the hole, I designed and printed some parts to attach a 1/4-20 bolt to a hole, hopefully securely enough to hold things up:

The very topmost part has the bolt threaded into it. It gets inserted in the hole and rotated 90 degrees so it can't fall out. The part just below it on the bolt has a 1/4 inch hole and slides up so the arms on either side stick through the hole and grab the top piece. Nothing can rotate now and with the plastic matching the shape of the hole, the clamping action should distribute the force quite well.

A captured 1/4-20 nut in a knurled knob is the screwed up the bolt to secure the top parts in place. The knob in the picture is a test piece I printed in PLA, but the final knobs will be in PETG so a hot trunk won't melt them.

That leaves a bolt sticking down which can be used to attach the remainder of the bag hook system (yet to be designed - probably a rod with hooks on it. I'll need to check how high my bags are and where they need support. Maybe a rope and some carabiners would be less complicated.)

Got the remaining bits printed in PETG, mounted them in the center of the holes so I'd have a little slack on either side:

Looks like the distance between the bolts is 25 3/4 inches. So that's how much space I have for whatever I'm gonna rig up.

I put a bag in the trunk to see how it fits, and the bag itself is below the bottom of the bolts, but the handles extend higher than the trunk itself, so they clearly aren't going to hang directly from the handles.

Perhaps a rod would be better than a rope. I can imagine a pair of hooks with the handles sliding through one to hook around the next one to take up all the slack in the handles.

I had a length of 1 inch square aluminum tubing which seemed like a good candidate. I cut a 36 inch piece of it and drilled 1/4 inch holes 25 3/4 inches apart centered on it. Fits quite nice, and there is enough bolt sticking out the bottom to hold a washer and a nut to secure everything:

Now I just have to figure out the hangers. What if I put some grommets up the bag handles just the right height to hang from the rod? (I can get a 1/2 inch grommet kit for 8 bucks from amazon :-).

Woa! In addition to grommets, amazon also sells hooks designed to hang from square 1 inch rods. I'm thinking off the shelf hooks and grommets are definitely the way to go (but I should get the hooks first to see exactly how big a grommet I need.) It will take a couple of weeks to get the hooks, maybe I should 3D print a copy of one to test for grommet size and position...

Here's my attempt at copying the hook shape from the dimensions given in the amazon description:

Here it is hanging on the rod:

I can't put it in the middle of the rod because there isn't enough vertical space, so I'll have to lower the rod to get the actual hooks on, but that means they won't fall off if they bounce when I hit a pot hole :-).

I decided I didn't want to have to have a wrench to assemble or disassemble this thing, so I printed another couple of knurled knobs with embedded nuts and now I can do everything by hand:

These printed without as much filament mess because I used gluestick on the top and bottom of the nuts. The filament actually stuck nicely instead of curling up off the cold metal.

At long last the real hooks arrived from China. My prototype 3D printed version was pretty accurate:

Now they are all up on the rod:

Last time I went to the store and had a full bag, I marked what looked like a good location (3 1/2 inches from top of bag) for the grommet on one bag by using the plastic hook, since the real versus plastic match was good, I guess I ought to go ahead and install grommets in one bag to try out the next time I go to the store:

The empty bag fits on the hooks just fine. The real test will be a full bag:

First trip to store after adding grommets, here's the trunk before heading home:

Here's the trunk after arriving home:

Looks like it was pretty effective. Even worked with the plastic bag (which I thought might have the handles break at the hook). The plastic bag I set on the side did fall over. I guess it is time to install grommets on the other bags and use this every week.