Smartwater Bottle Cap Retainer

[DONALD J B]

Used my laser cutter to make the tether seen above. What’s not completely clear is that the cap can spin independent of the tether (I tightened the self-locking nut on top then backed it off a hair).  Seems to work great.  I designed a custom cap and had some sampled 3D printed that will be here on Friday that streamline that top a LOT.  No more nut and bolt, just a mushroom of plastic on top.  Works just like the Nalgene bottle caps, but should work for any soda bottle depending on the size of the ring under the cap, anyway.  And since that part is laser cut out of pretty cheap material, that part is easy to change for other bottles, too.  And this should still work perfectly with the backpack shoulder strap clip from Zpacks.

It’s also easy to transfer between bottles.  To install, you basically just remove your cap and cut off the safety-ring that is left below it.  Then you just insert the bottle through the hole of the tether and work it over the ring below the threads. Comes off with a little work, but won’t come off too easily.

–Donnie

[MJ H]

Does it leak?

[DONALD J B]

Nope.  i didn’t *really* care if it did since this was just to see if the tether was strong enough and seemed like it would work, because the next step is a cap that’s one piece again.

But I flipped it over full and squeezed pretty good.  Nothing.  Left it sitting full laying on its side in my truck for a few hours.  Nothing. So it *is* safe to do it this way.  I used an aluminum screw since I did plan to drink from it and didn’t want to have to worry about corrosion inside, though.

–Donnie

[Ken Thompson]

Does it weigh more than a spare cap?

[MJ H]

Losing a cap in the woods isn’t LNT.

[Ken Thompson]

Well I’m not asking for myself, obviously,lol.

[Rex Sanders]

My solution for not losing Smartwater bottle caps costs $1.49 at stores everywhere, transfers from bottle to bottle with a couple of twists, doesn’t leak under normal use, and comes with 700 ml of free water:

— Rex

[David Caudwell]

I use the same: sports cap lids from either Smart Water or Life Water bottles. These can also be used to back-flush any of the Sawyer filters in the field.

[DONALD J B]

I haven’t weighed it yet, but should be similar or less than that of a spare cap once I have a new cap made and get rid of the nut/bolt.

Pros:

• Can’t lose it
• Can’t drop it and get it dirty
• Provides point to tether
• don’t need to remember a spare

Cons:

• extra weight
• costs money

There are other ways to tether the bottle in your pack, but a small caribiner to this tether should be something you can easily one-hand. This feature is important to me as I like to be able to bend over without worrying about dumping my water bottles on the ground, and these things don’t want to stay in the pocket of a pack when full since they’re so slick (Smartwater bottles, that is).

 

–Donnie

 

[Paul French]

Donnie,

Congratulation on your creativity. Keep up the good work. You have convinced he that my minimalist

mesh water bottle pocket idea needs to be shelved.

Paul

[DONALD J B]

Finally got another iteration done:

So that’s the 3D printed cap along with an HDPE retainer. Can’t cut HDPE with the laser because it melts it too easily, but I have a CNC router working now and I cut it with that. Will be testing this iteration now.

The cap shown by Rex a couple posts up is a reasonable solution as well, but it’s heavier and you can still drop it and get it dirty while you remove it completely to fill your bottle. Also doesn’t flow as much water when pouring, and I like to drink fast.  :)

 

–Donnie

[Roger Caffin]

My solution is to carry a spare bottle cap in my repair kit. This is a really good solution, because it means that I have never lost a bottle cap in the field (since I have a spare and Murphy gives up).

Actually, a lot of drink bottle have a similar arrangement, although usually for bigger lids.

Cheers

[DONALD J B]

Yes, this design is stolen directly from Nalgene (among others). I actually ran into someone who worked on Nalgene’s design and it turns out they use a special process to press and “weld” their cap nub through the tether.

That said, I took a spare cap to Nepal and thus did not need it. I’d probably STILL take a spare even with my setup above because anything can happen.

What I also like about my solution is it provides a very easy tether point, too, to help keep from losing the entire bottle.

–Donnie

[Roger Caffin]

I’d probably STILL take a spare even with my setup
I do too. :)

Cheers

[Lester Moore]

Excellent idea Donald – do you plan to sell the CNC HDPE version in the future?

[DONALD J B]

I would if I thought there was interest, but I’m not sure there is.  For now I still need to test it, though.  The first version was a modified acrylic and it lasted a full week of pretty hard use before it snapped.

–Donnie

[Roger Caffin]

I would definitely not use an acrylic. I suggest you try 1.5 – 2.0 mm polyethylene. eBay is your friend.

Cheers

[DONALD J B]

Well, like I said, that was the first one and it was modified acrylic.  It’s actually pretty neat stuff, but yeah, didn’t quite work.  But the HDPE seems to be holding up, which is basically what you’re suggesting (exept that’s really thick and wouldn’t bend well at all).

 

–Donnie

[Roger Caffin]

Either go thinner, or try a heat gun GENTLY to get it into shape.

Cheers

[DONALD J B]

I’m using HDPE for the latest version, which is high density polyethylene. It’s about 0.06” thick sheet.  Are you suggesting something different?  This bends fine, no heat required.

 

—Donnie

[Roger Caffin]

Seems exactly right to me.

Cheers

[DONALD J B]

I think I found the Achilles heel.  I’m not sure there’s a material you can 3D print that’s not going to come out much more brittle overall than the injection molded caps.  I dropped my nearly full bottle from about 4′ onto concrete.  It landed right on the cap.  The 3D printed cap shattered.

I haven’t done any more testing, but I’d guess the original cap handles that situation most of the time without breaking.

That’s not enough to make me not use my solution on a backpacking trip, but I’d definitely carry a spare (likely original) cap. But it probably is enough to make me not bother pursuing selling any of these. There’s no way it’s worthwhile to try to injection mold (my understanding is the initial investment would be $10k or more).  But it was a fun learning project and I got some stuff I can use out of it, which was all I really hoped for.

–Donnie

[Roger Caffin]

The original bottle caps are some sort of injection-molded PE or harder PE blend. They do not shatter.
I have impact-tested a few like this: very robust. Typically a 4 m drop onto hard rock with a 1.25 L PET rocket-based bottle full of water. Zero failures.

Cheers

[Author]

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