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Why soda bottles have gaps in their threads (2000) (madsci.org)
406 points by jfrunyon 3 months ago | hide | past | favorite | 127 comments



Since the article mentions it, the amount of carbonation in any given beverage actually varies by a lot. The traditional measurement of carbonation is in "volumes", which is the amount of space the CO2 would take up at standard temperature and pressure (32F and 1 atm). Coca Cola is usually packaged at 3 volumes; if you took all the CO2 out of the soda it would occupy 3x the volume of the soda it came from.

Alcoholic beverages on the other hand have a pretty wide range of regular carbonation levels. On your lower end you have stouts and Scottish ales at 1.9-2.1, and on the high end you get your dubbel and heffe weisen at 3-3.5 volumes. Champagne is regularly in the 4.5-6 range, which necessitates a different bottle and closure design to handle the 2-3x pressure it contains compared to beer.

On a particularly dumb note, ciders are limited by law to 0.64g per 100ml, or 3.2 volumes. Above that level they cease being ciders and instead become a sparkling wine. This is very important because natural cider is taxed at $0.226 per gallon, while sparkling wine is taxed at $3.30 or $3.40 per gallon depending on how the carbonation is added. This is a difference of roughly 30 cents per standard bottle, or $1.79 per six pack; enough of a difference to make similar products more attractive on the market place shelf.

https://www.ttb.gov/tax-audit/quick-reference-guide-to-wine-...


> On a particularly dumb note, ciders are limited by law to 0.64g per 100ml, or 3.2 volumes. Above that level they cease being ciders and instead become a sparkling wine. This is very important because natural cider is taxed at $0.226 per gallon, while sparkling wine is taxed at $3.30 or $3.40 per gallon depending on how the carbonation is added. This is a difference of roughly 30 cents per standard bottle, or $1.79 per six pack; enough of a difference to make similar products more attractive on the market place shelf.

I've seen this with chocolate too. The definition of chocolate in the UK and EU apparently requires one of the ingredients to be sugar, making sugar-free chocolate unable to be called chocolate unless it actually contains sugar. A friend of mine runs a keto chocolate company and he has to include a small amount of coconut sap to actually be allowed to market it as chocolate, even though he's trying to minimise carbohydrate content.

On the one hand, this seems a rather silly law, but on the other hand, how else do you define what a particular product is? Is it down to how it's marketed? Because then companies will just market it as something else that still hints it's the thing it's not, to avoid the tax and potentially gain more price-conscious customers.


  > "how else do you define what a particular product is?"
  > "companies will just market it as something else that still hints it's the thing it's not"
Through extraordinarily detailed discussions of its characteristics (e.g. when it goes stale, does it go hard, or soft?)

Jaffa "Cakes": https://en.wikipedia.org/wiki/Jaffa_Cakes#Legal_status


That kind of exemplifies a very British problem that we have with very vague and increasingly slow bureaucracy. There’s often no clear cut answer to a question. I think it’s one of the reasons why we get the least amount of productive work done per hour in Western Europe. In our national mythology we think of ourselves as a low bureaucracy country compared to say France, but in actual fact in those countries you will quickly be told no if something is not permitted whereas here there’s a lot of equivocating until, after 6 months of uncertainty you reach a seemingly random semi compromise result.


That's an interesting observation.


After reading that, I have a new appreciation for the page’s opening sentence: “Jaffa Cakes are biscuit-sized cakes …”


Do you mean unsweetened instead of sugar-free (though that would sound... odd)? Because I know several brands of sugar-free chocolate in Finland that are sold as just that, sugar-free chocolate. They usually contain maltitol, aspartame, or some other sweetener.


Possibly there needs to be something classified as a sweetener, yes, but the definition of "sugar-free" is apparently also anything with 0.1g or less sugar per 100g, so may it be that there is still a bit of sugar in the sugar-free brands you mentioned?

I'm no expert on this.


Looks like in the EU "sugar free" is limited at 0.5g sugar per 100g or ml of product: https://ec.europa.eu/food/safety/labelling-and-nutrition/nut...

I checked one and it contains 0.1g of sugar per 100g, but it's not added sugar, it's contained in the other ingredients. I don't know if it's possible to make it with absolutely 0g of sugar. But there is no separate ingredient "sugar" there.


You know what's even dumber? Having a product that can vary in price 1000x or more...and taxing it by volume, instead of by its price.

Yet another way the rich shift more tax burden away from themselves. They pay a pittance of a tax on a $5,000 bottle of wine, while everyone buying "two buck chuck" at Trader Joes ($3-4/bottle) is getting hit with a huge tax percentage-wise.

Even taxing alcohol at different rates just because it's made with specific fruits is idiotic. It smacks of lobbyists buying off their congressional reps to get a rival sub-industry slapped with a higher tax. Just tax alcohol by its value, across the board at the same rate.


If alcohol is taxed based on public health and safety concerns, it makes sense that the tax is proportional to the amount on neat alcohol contained in a product rather than the price of the product. Or maybe even a "progressive" tax, if we consider things like distilled spirits to cause more rowdy behavior and other kinds of disturbances.


Usually the people getting rowdy are drinking cheapo lager or whatever as they know you’ll get more alcohol per unit currency that way.


Yes, but there is an argument to be made that if the best 'bang per buck' would be distilled spirits, the problem with rowdy drinkers would be even worse, as a bottle of cheap vodka/whisky/whatever is more portable, and particularly for younger more inexperienced people it's much easier to drink it too fast and end up in the ER getting your stomach pumped.


If alcohol were taxed on public health concerns it would be a tax based on the percentage of alcohol, not CO2 content.


Absolutely. While I didn't address that point in my reply, yes, taxing beverages based on the CO2 content is ridiculous.


it is not taxed on CO2 content, it is taxed by marketing category and those categories have CO2 as a factor.


Ha, coincidentally they just announced they are finally fixing this in the UK.


There is a tax on CO2 in drinks?


Indirectly, the difference between ciders and sparkling wine is CO2 content but it’s a binary difference where in rising CO2 within each range has zero tax implications.


Even dumber is the practice of banning things. For example, California is banning gas powered leaf blowers and chain saws. This is going to cause a problem for people who need to clear downed trees during a power outage after a storm.

The usual solution is to carve out a bunch of exceptions. These exceptions tend to be incomplete and don't evolved with the times.

A far better solution is to just tax the ICEs that drive these things. Make it so that for most mundane uses, the electric ones will be cheaper. But the people who really need them can get them without mounting a lobbying campaign at the politicians.


> A far better solution is to just tax the ICEs that drive these things.

Even simpler and more effective is raising fossil fuel taxes. If the goal is to reduce usage of fossil fuels.

If the goal is to look like you are doing something about fossil fuel consumption, but do not really want to give up your SUV/pickup trucks, extraneous driving, life in large houses in spread out cities, and frivolous flights, then selectively targeting certain products is the way to go.


The issue with these small machines like lawn mowers and chainsaw is not really they CO2 the pump out, which is minuscule compared to all the other sources of CO2, but rather that they have zero pollution controls and put out a lot of particulates, unburned hydrocarbons and whatnot. It's a question of local pollution, not global climate.

And further, since your average homeowner doesn't use his chainsaw or lawn mower that much, they are relatively insensitive to the price of gas. Or IOW, if you were to raise the price of gas enough to reduce usage of these machines that way, it'd grind the whole economy to a halt.


> Even simpler and more effective is raising fossil fuel taxes.

In general I agree with you, and that ought to be done for cars. But those small engines tend to be very dirty polluters, and it would be impractical to put an extra tax on gasoline meant for those engines.

A reasonable tax would be $50 to $100. The state is good at taxing in this manner, and the revenue could be used to subsidize some green project (though we both know the tax revenue will just be wasted, sigh).


Wait till all of your neighbors start wielding battery powered blowers. The high pitched whine will leave you wishing for the the old 2 cycle motors.

It would be trivial to tax blowers in a pollution basis - they either use a 50:1 premixed fuel or you add oil to regular gas. Just tax the oil.


My electric lawn mower is so much more reliable and quieter than my old 2 stroke gas mower. I don't live in California, but either way, I'd refuse to go back to using a 2 stroke.


Mowers aren’t 2-stroke engines, and don’t pollute as much. (2 strokes combust the lubricant)


No, it won't. My street has voluntarily already done this. It's very quiet now.


There exists 4 stroke leaf blowers that do not require oil in the fuel, though.


Yeah, they are great but usually for commercial use — usually big, expensive and heavy. If you have a big yard, there’s a gap between a battery powered blower or weed whacker and gas.

Personally, i think battery powered lawn gear is winning the consumer market as it is, banning stuff is just forcing people to accept inferior solutions for their needs.


Yes, I guess if the problem is specifically these machines, then a sufficiently high tax to bring their usage down would work better.


> California is banning gas powered leaf blowers and chain saws.

The state is doing no such thing, it is however

> California is banning [the sales of new] gas powered leaf blowers and chain saws [after 2024]

There is a significant difference.


The engines in those wear out after a time. A home owner can use the same saw for years, but a pro using it for a full workday will replace it every few years.


battery powered versions work fine, and tend to be quieter as a bonus


Perhaps for leaf blowers that it's all upside - but for good size chainsaws say something that can drive a 24" bar, electric just isn't available.

I love my electric 18"er, but most all of the ponderosas I have to fell on my property require my 24" gas Husquavarna. And if you look for electric alternatives you find nothing for actually for sale.


I agree in general, and my own chainsaw is battery powered. However this is about a major storm/outage. My batteries (if I can find them all and they are charged) give me about an hour of cutting before they are dead. That is not enough to clear out a storm. I know pros sometimes have battery backbacks that will run all day, but they still need a way to get that battery charged overnight so they can run again the next day. I know people who have been without power for several weeks after a major storm, so one day isn't enough for crews to clean up.


Is the extra backpack harder to store than the extra gallon tank of gas in the trailer? It's not like they can refill the gas tanks without pumps working at the gas station. If they do have access to gasoline, with modern trucks they should be able to charge from the IC engine.


Each backpack is $1000. A gas can is $20. Both are sometimes stolen from the back of trucks, but one is worth enough that it a big deal.


Interesting, I didn't realize the backpacks are so expensive.

Perhaps one of the effects of a ban on sale will be the development of more practical and accessible, from a price perspective, power sources?


You didn't know that batteries were more expensive than tanks?


I didn't know the battery packs were so expensive that having them in a landscaping work truck was a substantial liability.


You've never bought batteries? Or, did you think that light weight and small yet powerful batteries were somehow inexpensive?

Whenever there's a discussion of using batteries for anything, the three issues that come up are cost, weight, and size. You can take a hit on one or two to get some improvement on the remainder, but...

Batteries for portable equipment must be good on weight and size given the power required, so cost is what goes up.


I know. People will be buying them from out of state, until other states ban sales, too.


What is significant? The outcome is the same.


People that just bought a leaf blower can still use it. Banning sales is therefore much better economically, and enforcement is also much simpler.


The lack of nuance in a ban is a bad fit for reality.


> You know what's even dumber? Having a product that can vary in price 1000x or more...and taxing it by volume, instead of by its price.

To be fair, this is just an excise tax on production. In most jurisdictions you'll also pay a percentage based sales tax on that as well. If you buy a bottle costing 2x as much, you'll pay 2x as much sales tax. Everywhere I've lived has had a pretty high sales tax on alcohol, in my current state I pay sales tax plus a volume based supplementary tax, the latter can get pretty high at $11.28 per gallon of distilled liquor.

Sales tax on discretionary and luxury products like this tend to be one of the few taxes that's actually somewhat progressive, given that the rich tend to consume a lot more in terms of dollar amount. Although in the case of alcohol, this would also hit addicts pretty hard.

> Even taxing alcohol at different rates just because it's made with specific fruits is idiotic. It smacks of lobbyists buying off their congressional reps to get a rival sub-industry slapped with a higher tax. Just tax alcohol by its value, across the board at the same rate.

Honestly, I think this is more about class than anything else. There is a long, sordid history of societies deciding that one type of alcohol is acceptable and classy, while another is base and to be suppressed. Usually the actual amount consumed doesn't seem to be a factor; nobody ever seems to get too mad at middle class and rich people for day drinking mimosas for example. My favorite cultural representation of this is "Beer Street and Gin Lane", which is both entertaining to me in its absurd hyperbole, and because I'm rather partial to gin.

https://en.wikipedia.org/wiki/Beer_Street_and_Gin_Lane

Personally, I'm mixed on what I think an ideal alcohol tax would be. It seems to me that we now have the ability to track the actual volume of pure ethanol created and sold, something that recently post-prohibition regulators probably were not capable of doing[0]. On the flip side I do think that there is some social utility in driving up the cost of high proof distilled alcohol via tax; the time before prohibition really shows that cheap distilled spirits tends to make a bit of a mess of things. This could probably be accomplished by a progressive taxation system per gram of ethanol based on the ABV above a certain point.

Thankfully most cider is pretty damned good at 2.5 to 3 volumes of CO2.

0 - The inputs into the fermentation process are a pretty good way to estimate what percentage of alcohol you'll get back out on average, which can be used as a rough means to regulate based on ABV if you lack the technical or governmental capability to test, track, and tax such things. Not all alcohol tax rules seem to use it this way though, such as the difference between cider and sparkling wine based on CO2 volumes, even if it's created by artificially carbonating it.


> Personally, I'm mixed on what I think an ideal alcohol tax would be. It seems to me that we now have the ability to track the actual volume of pure ethanol created and sold, something that recently post-prohibition regulators probably were not capable of doing[0]. On the flip side I do think that there is some social utility in driving up the cost of high proof distilled alcohol via tax; the time before prohibition really shows that cheap distilled spirits tends to make a bit of a mess of things. This could probably be accomplished by a progressive taxation system per gram of ethanol based on the ABV above a certain point.

Broadly I agree, though I think in practice it would make life easier if this would be specified in "bands" rather than directly proportional to the alcohol content. The giant industrial scale producers can certainly produce mega-batch after mega-batch of identical product, but for small scale "craft" producers with more variability it sounds like a bureaucratic nightmare to have a different tax level for each batch.


> The giant industrial scale producers can certainly produce mega-batch after mega-batch of identical product, but for small scale "craft" producers with more variability it sounds like a bureaucratic nightmare to have a different tax level for each batch.

That variability is already allowed (in the UK at least, but not banding) and comrs with an unexpected side effect - large brewers were advertising at higher abv values then they were brewing at, but paying duty kn the lower value [0]. taxing by abv simplifies the cslculatuons; you just measure it once.

[0] https://www.bbc.co.uk/news/uk-41059610


> That variability is already allowed (in the UK at least, but not banding) and comrs with an unexpected side effect - large brewers were advertising at higher abv values then they were brewing at, but paying duty kn the lower value [0].

You didn't expect them to forego an opportunity to shaft BOTH the consumer and the taxman at the same time, did you?


Is there not sales tax on it then?


Why is standard temperature the freezing point? Why not 70F or 20C or something more within the range of normal experience? We didn't set 1 atmosphere as the atmospheric pressure experienced at the average altitude in the Himalayas.


> Why not 70F or 20C or something more within the range of normal experience?

FWIW that is literally a thing and it is seriously called "normal temperature and pressure".


There are a lot of slightly different standards for temperature and pressure: https://en.wikipedia.org/wiki/Standard_conditions_for_temper...


How are you going to set the temperature of your sample to 20C before you measure it? Freezing point can easily be achieved with an ice bath.


Whoa, the numerical carbonation levels actually correspond pretty well to my memory of how “fizzy” those drinks taste on the tongue. This is the coolest trivia I’ve learned in awhile.


Though some what off topic: Even though style may dictate a different carbonation level. Draft beer is typically carbonated to around 2.4 volumes so it pours on most draft systems at bars. If you carbonate beer to far above this amount of volumes, the beer won't pour well. That is one reason why certain styles may taste different in a bottle versus on draft.


Putting gaps in is also a useful trick to have up your sleeve if you're 3d printing internal threads. If you print threads as continuous bodies, the filament on each layer is effectively a ring which is (because of thread geometry) less supported for part of its length. When it contracts slightly as it cools, it can pull the overhang section of the thread away from the body of the object, and you end up with loose filament strung across the gap.

If you cut gaps along the thread, when it prints you're effectively building a lot of small separated ledges out from a side wall. You don't have that cooling/tensioning effect and there's nothing to pull the filament away from where it's laid down so you end up with a cleaner thread.

That's as long as your retraction settings are well tuned, mind - continuous thread is one long extrusion with no retractions, whereas thread with gaps is potentially lots of islands, depending on how your slicer reacts to the geometry.


I assume this happens on very small threads and/or with thick layers?

I print both depending on size, and a full thread is usually more self-supported, not _less_, while printing faster to booth. Toothed threads tend to suffer from curling more easily when comparing at the same overhang slope, and are weaker structurally.

I'm using toothed threads for larger threads to save on time/material usually, or oddball constraints.

I can see why you would get the effect you're describing, but this would only happen if you're printing with insufficient Z resolution in order to support the overhang of the thread. I cannot see how a toothed thread would improve in such a scenario.


Yes, small threads in particular are prone to this. Although the first thread I needed it on was 2mm pitch with 0.2mm layer height, so not that small.


I'm a bit surprised by this. 2mm pitches are well printable at .2, although I usually don't use the stand ANSI/DIN profiles, but limit the overhang profiles manually depending on the material (from 45 up to 70, really) to improve them. Still, at 2mm, this shouldn't be necessary.

Maybe the slicer you're using is doing something odd.

Keep in mind that if the filament string looks pulled in a full thread, a toothed thread with the same settings will be even weaker. In such cases it will change the result to localized sagging areas, where the structural element is just the start/end of each tooth.

A screw, even plastic one, will easily self-thread into the thin amount of plastic remaining, but that doesn't mean that the thread works as intended structurally.

If you have issues with smaller threads my reccomendation is to print an undersized cylinder and use a tap for best results, or just slightly undersize the hole and self-thread instead.


You can also achieve this effect by making a multi-start thread. This increases the anchor points per layer.


My country's national library used to provide a service in the 70s/80s where you could send a letter or telegram with a question, any question, and they'd do their best to answer it.

My Mum was a big fan of it, I've still got a copy of their telegram response to her question of "Why don't we see birds flying overhead with a penis flopping around?"

The answer was simple.

"Most birds don't have penises. They press cloaca to cloaca. Birds that do have penises store them in their bodies when not mating. Please stop sending questions about penises"

...it wasn't her first animal penis question submitted, and I'm assuming she'd developed a reputation.


That's fascinating. I can remember pre-internet days being resigned to not knowing stuff. For example albums in my country generally didn't include the lyrics. Every time it came on the radio, I asked people what was the singer saying over and over in REM's "The sidewinder sleeps tonight". Nobody knew. Another was a foreign language pop song I remembered from when I was on holiday abroad as a teenager. I searched fruitlessly for it in record shops at home. Decades later, on a whim I found it by googling and then the original video on youtube (I'd only heard it on juke boxes)


In college in Washington, DC, in 1987 or so, drinking after hours in a bar (at about 3:30AM) we were having a argument over which was the capital and which was the largest city in Scotland. Not reaching any agreement, the bartender wisely realized that the British Embassy would have a duty officer on, who he called from the bar, and who quite happily answered all of our questions and settled the argument.


Very good! That actually reminds me of a similar story from a very well known sportscaster in my country who specialty was, say, rugby. One night he was on duty when a call came in from someone trying to settle a argument about soccer, something like which team had won the most soccer league titles A or B. He replied that he wasn't an expert but he was pretty sure it was team A. Silence on the line, then the voice came back asking Is that Joe Bloggs?, he replied that it was and then the voice said and what the fuck would you know about it? and hung up.


This is the origin of the Guinness book of records: Guinness sent it to pubs as a fun advertising gimmick.

In the days of poor information diffusion I guess content marketing was even more important than today: the Michelin Guide was similar: the tyre company wanted to encourage people to drive more, and figured the guide book would not only help with that but people would have the name Michelin in front of them. Hence the star ranking (go if you’re in town; if you’re in the area, worth diverting your trip a bit; worth making a special trip).

I actually used to jokingly call the iPhone “the destroyer of bar bets” but after a year or so on the market those discussions had pretty much died off, so maybe it wasn’t a joke.


Those same dynamics made meeting people fun and important! Who one could get in touch with really mattered.


My children are still baffled about how we researched things before Google.

And I'm saddened when I have to say "Well, we went to the library, and we hoped their encyclopaedia wasn't too racist".

In fact, as a kid I learned to use certain countries as a sort of metric of an encyclopaedia's relevance - if it discussed Rhodesia in the current tense, be very careful with anything else in it.


I've seen ducks mating. For their body size, they have magnificent penises. Flying with these things flopping around would not only be very difficult without getting caught in something, it would also be extremely irritating to people.



No way I am giving Google my passport or my debit card anyway, so I’ll die an ignorant.



Cheers!

It is probably the first time I thank someone for showing me a duck’s penis. Feels a bit weird.


Feels weird? May I ask what peripherals you have on your computer?


This is definitely in the top 10 funniest things I've read on the internet. The fact that they reluctantly answered the question is incredible.


https://www.bbc.co.uk/programmes/m000tcbk

From the Goodreads blurb: ”a novel focused on the letters exchanged between Tina, a hardworking farm wife of three children and a museum curator and widower named Anders in Denmark. Their unlikely correspondence begins when Tina's seeks more information about the museum's most famous exhibit.”


Who remembers literally having to remember dozens of phone numbers off the top of your head? With no internet to look it up one would either have to have a phone book handy or remember numbers in your head. Which is funny because one of the main numbers I remember learning was the movie theater movie line where you could get info about what movies where playing.


I wish I had a photo, but yes!

I find it hard to recall a contact number today. We get to use names, so that skill drops off quick.

Growing up, we had a wall mounted phone with an insane cord. Something like 15 to 20 feet so people could take a call and walk into the adjacent room.

One day, I wrote an important number next to the phone on the wall, and it started! Mom asked about it, and said something about writing on the wall being bad. I said something about the difference, because it is easy, right there, won't get lost..

She then put the school, family, few other things next to it. Instant buy in! I remember feeling good about that, like we did something that matters and was unorthodox.

I took one last look at it before moving out and into my life:

There it was. Our lives on the wall next to the phone. That pizza place, family, services, church, schools, friends, and other bits: birthdays, various identifiers, locations.

When I left, that on the wall directory was damn near a square meter!

A phone book was right below on a little stand. Actually two: the local one, very small. And the yellow pages. Huge.

One day, my brother drank gasoline! I was the only one home and sure enough! The little green poison control sticker was on that wall, next to the phone. Called them and they told me what to do, until someone could respond.


Seattle Public Library has this. You can even chat with them online. (I'm not linking to it because I'm not sure they want the attention.)

My friend works there. She loves interesting questions -- probably even about penises. Unfortunately she says a lot of old folks use it just ease their loneliness and to ask tech support questions.


That is both beautiful and sad.


Your mum had a solid sense of humor.


In the early 00s there were a number of text services providing the same function. I got banned from one for the questions "What is the collective noun for a clitoris?" and "What is the resonant frequency of a clitoris?"

I imagine they were a fun place to work at 2am.


The Berkeley, California Public Library used to have an "after-hours reference librarian" on duty in the late 1970s or so. You could call up in the evening and ask them a question.

I remember once calling and asking how much Vitamin C was in an orange, waiting on hold for a minute or two, and then getting the answer.


Wikipedia offers a similar service: https://en.wikipedia.org/wiki/Wikipedia:Reference_desk


I was aware of the cloacas, but I didn't know that some birds do have penises, so thanks for that important info! BTW some mammals (notably cats and dogs) also "store" their penises when not mating...


You might enjoy researching the duck’s reproductive system.


Do you happen to recall the other questions/responses?


That's so fascinating!

Picture:

http://preview.turbosquid.com/Preview/2014/07/11__16_24_14/P...

More discussion:

https://www.reddit.com/r/AskEngineers/comments/372h8x/why_th...

Last weekend, on my way to the supermarket, I saw a juice bottle blocking a drain. To follow UncleBob's advice to clean as I go, I picked it up.

https://www.youtube.com/watch?v=BSaAMQVq01E&t=2021s

I wanted to pour out the remaining orange juice for a nearby tree to get its vitamins. Pop! The cap flew off, lightly knocking off my forehead, but with much force. Thank God it didn't shoot into my eye, it was quite powerful.

Although it wasn't a fizzy drink by design, the juice had fermented in the hot sun.

Today I learned that there's a solution to the cap flying off, using a different design of screw thread! Thank you jfrunyon for posting this to Hacker News so we can all learn from each other :)


> The cap flew off, lightly knocking off my forehead, but with much force.

I have a vague memory from the 80s of a UK consumer show ("Watchdog" or "That's Life") highlighting the dangers of opening pop bottles with your teeth because the caps could fly off and smash your teeth / soft palate etc. Not finding anything from the searches though.


I remember some concern about bottle and jar openers without guards meaning the cap on a soda bottle could hit the user on the eye. I think my mum quietly "stole" the one my grandma had, since her grip was becoming a bit weak.

https://www.istockphoto.com/photo/bottle-jar-opener-made-fro...


Here is what I believe to be the original patent from 1979 as well https://data.epo.org/publication-server/document?iDocId=1031...


I figured this out once myself. I had dropped my Coke plastic cap, so to replace it I took a metal cap from a non-carbonated drink (maybe water) that was of the same size.

When I eventually opened the bottle it basically shot my hand off with some speed and shock.

I was quite surprised and then investigated and found the gaps, it's a neat little addition to the design (and makes one wonder how many other little details like this there are in daily life products that we'll never even know about).


> makes one wonder how many other little details like this there are in daily life products that we'll never even know about

You notice the hard way when you try to build things yourself. All the small things that make mechanics go together ... like just getting the jiggle just right to make things not seize or be too loose.

The amount of institutional knowledge around is insane, and I fear that the quality drop in things in recent years is just not due to cheap imports, but also that employee employer loyalty is punished by the employers nowadays and they are losing experienced engineers. Like the "I'll be designing cupboard hatches here till I retire"-generation is retiring and the new engineers are job-hoping?


>>> (and makes one wonder how many other little details like this there are in daily life products that we'll never even know about).

That's what I find most interesting about things like that. They are everywhere and its a joy to find them.


In a similar vein, I found this explanation [0] of how and why a soda can's tab functions the way it does to be fascinating. Very clever and elegant solution to the problem of opening a can under pressure.

0: https://www.youtube.com/watch?v=hUhisi2FBuw


Engineerguy's youtube channel is a real gem, and I wish he made more videos. Every topic he's picked has made the subject matter interesting, even about the really mundane things like baby diaper design. My substitute channels in the meantime have been Practical Engineering and Applied Science, but those two don't really have the level of depth or polish (respectively) as Engineerguy.


Practical engineering is up there. I will check out Applied Science.

In a similar vein I recommend Not Just Bikes and City Beautiful for city planning details you haven’t thought of. It’s less expert advice and more observations, at least for NJB, but it’s eye opening!

And of course, Technology Connections.


Applied Science is just a really smart guy who works (worked?) at Valve who reads cutting edge research papers and tries to recreate it in his home machine shop / garage.

I just discovered Not Just Bikes a few weeks ago, and I'm really digging his content. He complains and rants too much for me to really binge his channel, but I still go back to it for small doses. I'll work my way through his catalogue eventually!

I do like Technology Connections, but I'm a mechanical engineer by training so a lot of his videos don't really cover new stuff for me, or it's a 22 minute video for 8 minutes of real content. He tends to go over each concept repeatedly from sliiightly different perspectives each time. Which is cool, but I end up skipping around in the video until he gets to the point.


Darn, wish I could have given you something new to watch, always love recommendations!

If you're into game design, check out Game Makers Toolkit; and New Frame Plus for animation.


No Clip also has good documentaries on how various games were made.


Half the time when I try to open the twist tie on a loaf of bread, it tightens. I called Arnold Bread to find out why the ties didn't consistently loosen counterclockwise. The explanation wasn't entirely satisfying, but the breads come off the production line and go to different twist-tie-applying machines which twist in different directions.


  > Non-pressurized packages (like bottled water) normally contain
  > smooth, non-vented threads since there is no internal
  > pressure to be relieved from the inside of the package.
Actually, some bottled water bottles do have the vents. Maybe to reduce the quantity of plastic in the bottle by another 1% without sacrificing rigidity in more critical areas? In some industries a 1% optimization of part of a process could be non-trivial, especially in a bottleneck component or material.


The greater saving is probably in using the same bottles / caps for still and sparkling water.


I noticed those gaps in the thread of a thermos (vacuum flask) last week. Presumably it’s to vent inward airflow when cooled liquid creates a vacuum.


Also, many thermos flasks have a feature whereby you can pour out the contents without unscrewing the lid all the way, so there will be a large channel interrupting the threads to allow liquid out, and one or more opposing interruptions to let air in.


Back in 199x plastic bottles with soda would sometimes explode inside the bag when we'd be walking on a hot day - it were earlier years of making soda in large plastic bottles in Russia and it was all "bottom line optimized" like visibly cheap low quality plastic, etc. And about 20 years ago a woman in Russia got her eye injured by the metal cap that flew off a soda bottle she tried to open. She sued the manufacturer ("Bravo" - once opened their metal cap had the lower band still attached and broken with couple sharp edges sticking out) - don't know the full results, yet the manufacturer started since then to use plastic caps instead of metal.


Back in the 1990s the UK TV programme "Watchdog" ran a report about projected bottle caps injuring people during opening. It was named "missiling". Since then I've always ensured that the cap is facing away from anyone when opening a pressurised bottle.

Funny how one short report can cause a lifelong change in behaviour.


Without the thread gaps, could the cap potentially be pushed off near the end with a lot of force?


Look at my other comment, but basically it's a surprising amount of pressure/force. If you're expecting it it shouldn't be a problem, but if not it can catch you unaware. It's a neat little design addition.



Based on the anecdote from peterburkimsher below, and not seeing any other reason to vent the pressure, I would guess so.


Yes the patent linked below includes this humorous introduction:

"In order to prevent "missiling" of the cap of a bottle or other screw-top container intended to contain a carbonaceous beverage, the screw-thread ridge 11 on the neck 13 of ..."


I think they mean gaps which run vertically. The thread is ‘interrupted’ and isn’t continuous. Thread spacing is normal, I don’t think they refer to this.


Definitely, this is what I envisioned they were describing (right side threads): https://www.capmakingmachine.com/Content/upload/2019330588/2...


I didn't know I wanted to know about this until I saw the link. Well done! :D


So what happens if there are no gaps, does the lid go flying off?


If I look at my bottle caps here in Germany, my 0.7l "soda" water bottles, don't have gaps. The Coca Cola glass 0.5l bottles don't have gaps either. Club Mate 0.5l doesn't have gaps. Only the Sprite bottle 1l has gaps. Handlingwise I don't notice any difference. Maybe because it's a learned technique thing, you twist it, let gas evaporate then open it. I don't even think about it.


I think this only works with PET bottles (the thin, elastic ones) as they work a bit like a balloon and can store more pressure energy.


Yes! It takes some practice but as a kid i managed to launch the lids off water and soda bottles that had previously been opened (more gas volume) and carried in a bag.

You need to edge the cap close to the point before the gas can escape, then give it a flick so it can twist open the last bit by inertia. Apply some pressure to the plastic bottle while doing so.

When it works the cap would fly off with a loud bang and the rapid change in pressure causes condensation inside the bottle, allowing you to push out clouds of vapor.

I think they changed the design of the bottle at some point and this would no longer work.


As kids, we would twist the thin plastic water bottles to compress the air inside, then launch the lids at each other as you described.


Apparently yes, read peter's comment:

https://news.ycombinator.com/item?id=28914869


Try putting some carbonated drink into a thermo flask with a sealed lid and open it after it's been in your bag.. the seal holds right to the end and the POP.

I have a hole in my kitchen ceiling from accidentally storing dry ice overnight in one too.


Now I wonder why they chose to use cuts rather than a slightly different thread form with a larger leak path.


This sounds like a 1990s Microsoftean interview question. Next up, manhole covers...


Hats off to Tony Smith, a stand-up fellow.




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