Hi JohnA. Thanks for asking. I found a good straight on picture of the bottle and used it as a background bitmap in Rhino (for Mac). I traced the outline of the bottle and did an offset to create the shell. Then I traced another curve along the profile to get the opening. it took me three times to get it right. The first model, I scaled incorrectly and ended up with something that was 30% too small..
The second version was scaled right, but my initial curve didn't hold the bottle firmly enough, so I made the top flaps a bit higher (causing the opening to narrow). It was kind of a balancing act as I wanted that opening at the top to be wide enough to easily squeeze the flexible bottle through, but narrow enough to hold the bottle in firmly.
At the same time, I wanted to make sure that I had a good area for drinking and holding water.
So, for the third version, when placed with the opening facing downward, a full bottle stays securely place. Then I wanted some kind of strap, so I punched in those holes. When I added the strap it also secured the bottle completely.
I had initially thought that I would hold it under my dog Elsie's mouth, but I realized that it is nice to set it down for a bit and let her come back to it. So I needed something on the bottom to stabilize it. I was just going to put a stabilizing rod, then realized that paw prints would be more fun. I also uploaded the version without the paw prints just in case someone wanted one that was cleaner.
I tried to configure the build to minimize supports as much as possible. The bottom definitely can use a bit of sanding and smoothing to remove the remnants from the supports.
Maybe this is more info than you want, but the project actually started with the cap. I just wanted a way for my family to reuse bottles at parties and stuff by marking them in a cool way. Then I thought Elsie needed a cap and realized that she should also have a little to-go bowl. Maybe soon, I'll be able to add a customizable version of the cap. I haven't done a customizer app yet, but I'm looking forward to learning it.
Sorry if this is too long, but you did ask!