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Shot tower (wikipedia.org)
269 points by ari_smith on Sept 12, 2013 | hide | past | favorite | 79 comments

In 1782, William Watts disrupted the shot ball industry by creating an unconvential simple solution that produced a cheaper, better output at a faster rate than the established method.

...How could any of you not understand how this applies to Hacker News? This is hacking at its finest!!!

I thought it was interesting that the modern "Bliemeister" manufacture method still consists of dropping molten lead drops. The difference apparently being the use of heated liquids and inclined surfaces for greater control. https://en.wikipedia.org/wiki/Bliemeister_method#Manufacture

In contrast metal bearing balls are manufactured using cold metal working techniques. Sheering, pressing, grinding and polishing some wire. https://en.wikipedia.org/wiki/Ball_%28bearing%29#Metal

It seems as if lead should be easier to press into shape than steel so I wonder why the difference in techniques.

Melting point of lead 327.46 °C, melting point of Iron 1538 °C. Additionally, I would assume that you have a lot less tolerances for bearing balls than for shot. So I assume that the much better process control for cold metal techniques is necessary for bearing balls.

> It seems as if lead should be easier to press into shape than steel so I wonder why the difference in techniques.

I only worked briefly in a cold-forging factory, but I remember there being issues with wire stiffness and difficulties with getting economical yield when making very small things. We were working with steel, brass and copper, so lead may be different.

Natural Bridge in Virginia¹ was used as a shot tower during the American Revolutionary War. They simply dropped molten lead off the bridge into the water below. Someone would then collect them from the stream bed after they cooled.

¹ http://en.wikipedia.org/wiki/Natural_Bridge_(Virginia)

Interesting ... when I visited I was struck by the fact that the salt-peter mine was used at that location (why not somewhere else rather than in proximity to the arch?), but didn't realize they also made shot there.

You can try something similar to this (although more related to the older barrel technique) at home with a soldering iron . Melt some tin at the tip while holding the iron at a sufficiently large enough height over a glass of water. It takes some practice to make nice round balls, but it works!

Loosely related anecdote: in a technical electronics high school my teacher showed us, as a cool trick to impress us, how to actually solder this way - you make a nice little ball from tin with the soldering iron, put it over the first pin of a multi-pin chip and let the ball freely fall through the other pins. It takes a lot of practice, but bits of tin stick to pins forming proper soldering joints and the (somewhat smaller) ball continues to fall. If you are good at it it's really faster then soldering each pin separately.

I'm very sceptical that such procedure would produce proper solder joints. Proper joint requires that both the lead/pin and the pad are heated. Some metallurgy guru could chime in and explain why that is.

When the metal is hot, solder remains melted, flows onto the metal and bonds to it. In fact, when soldering you should heat only the metal parts first and not the solder directly, and then apply the solder to the metal parts where the soldering iron touches them. You never heat solder directly with the soldering iron and expect it to stick to cold metal.

When the metal is cold, the molten solder freezes up as it touches it, making electrical contact but not really sticking. So sometime later, as a result of thermal expansion or mechanical flexing, the solder joint becomes unstuck. This is called a "cold joint".

It's also essential to use flux when soldering. Most solders used in electronic hand-soldering have a rosin flux core in the middle. The rosin melts first onto the metal you're heating, preventing the heat from forming an oxide layer so the solder can bond to the metal. (I think the flux also helps break down any existing oxide layer, not too sure on that part.)

This teacher's technique would result in unreliable cold joints all up and down the pins.

Search for "cold solder joint" for more information and photos of cold joints.

It sounded like a bad description of drag soldering which involves dragging a ball of solder over the pins with the iron and relying on the solder mask and surface tension to make a good connection on each pin.

Yes, judging from YT videos of drag soldering, this was what he did, except unlike people in those videos, he did it holding the circuit board vertically and hence it was one very quick move. Bear with me: this was almost ten years ago, I had nothing to do with electronics since, and I am not a native speaker of English!

Friendly reminder to exercise common sense when you do this. Wear eye protection, long sleeves, possibly gloves. And ffs DON'T FLING THE IRON. Your aim is not as good as you think it is. :-)

Also, lead. Don't use a drinking glass.

>Also, lead. Don't use a drinking glass.

I can't check it for myself now but I assume this would also work with lead-free solder. Not that you should put any kind of solder in your drinking glass.

I did this, but using lead. Yes, I was young and stupid. It did work nicely though.

Also, at school, our chemistry teacher heated a rod of glass and asked a boy (who was grabbing an end of the rod in pliers) to run across the room, creating a thin thread of glass.

I don't think they'd do that in schools today, but maybe I'm wrong.

In what way is practice useful here? Determining the correct height to get good spheres, having a steady hand when dropping it?

It's been some time since I did this, but yes, it's mostly the correct height + keeping the hand steady when the drop falls. I think getting the height right is more critical. You need enough time to have the drop cool down. On the other hand, higher means also larger impact which can splat the drop more easily.

I would imagine that could be solved by keeping the water at or near a boiling point; breaking the surface tension of the water while still being cool enough to let the tin completely solidify.

Try it.

Ok, I get it, not HN material. But, write a blog post about creativity and simple solutions in startups, using shot towers as an illustration, and boom goes the dynamite. This post requires us to use our imagination and extrapolate to get the point, I guess.

This is what I took from it as well: simple solutions can work really well. We shouldn't always try to tack on the fashionable and new pieces of tech to make something work when we could keep it simple.

On top of that, I learned how to make metal spheres with physics,some history and saw a bunch of pretty pictures of old towers. All in all time well spent.

Interesting. So in essence, the 19th century used zero gravity fabrication. Who knew?

And for a more continuous process -- did you ever wonder how long straight glass tubes were made?


I used to live near this.

I've lived in Dubuque, IA (there's a picture of our shot tower in the article) my entire life, and assumed that everyone knew what these were. It's a iconic symbol in our city's history. I guess I took them for granted.

I currently live in the Dubuque IA area, and felt the same way (I moved here in 2002 from Wisconsin)

Me too, I lived in Bristol (also in the article, and where the original inventor lived). Sadly the shot tower has since shut down and been converted to a penthouse (I think - the article says offices, but I'm 99% sure the tower itself became an apartment).

Same. I stopped by the one in Wisconsin (on canoe trips) frequently as a kid. I thought they were common.

Is the factory at all noisy? I'd imagine dropping massive lead spheres could cause a ruckus.

I think any metal working shop will be noisy. From watching documentaries metal heating furnaces are really loud.

The Dubuque shot tower does not operate anymore.

I couldn't find any videos of shot towers in action, but I did find a video of a man demonstrating a handmade modern shot manufacturing machine: http://www.youtube.com/watch?v=TwVvdIFyQ0Q

Wow that's a pretty amazing machine, thanks for sharing that video. There are very few things in terms of web engineering that I think I wouldn't be able to figure out, but when I look at stuff like that, that one guy just built, I am so impressed.

Interestingly, we in Latvia still have a shot factory which produces shots this way: http://www.dsr.lv/?lang=en

This is also how you create urea in prill form, which you'll find in a bag of fertilizer.


I saw the picture of the Clifton Hill shot tower at the top there and thought—“hey, that looks like—”. I’ve wondered precisely what it was meant to be every time I’ve passed it (not very frequently), but never enough to find out.

Cool stuff, even if I don’t quite see how it's relevant here. :P

How many feet taller does a tower in northern Alaska need to be compared to one in south Florida? (at 0 feet above average sea level)

Someone please calculate this.

Thank you.

I'd imagine it would actually be shorter because the ambient temperature in Northern Alaska will be much cooler than that in South Florida, so the shot will cool faster.

It also depends on the diameter of the shot you wish to produce.

There's probably much more water vapour in the air in South Florida, which means there's more thermal mass available - I wonder if it would be enough to have an effect?

I'm thinking that with more thermal mass in the way of the droplet, there's more chance to offload heat, and the difference in ambient temperatures is small compared to the difference to the melting point of lead (>300 deg C)

...to achieve what?

For the balls to form - the Earth isn't a perfect sphere and gravity in alaska is ever-so-slightly greater than further south. (Which means the tower needs to be taller, so the ball is in the air longer)

It sure helps that its colder in Alaska than in Florida. However, I don't know if that compensates the smaller gravity.

That's an interesting interpretation, but I assumed they were referring to the temperature difference.


It's been turned into an enclosed mall in the Melbourne (Australia) CBD. You can see the glass dome covering the whole shot tower building from all over Melbourne.

This is also how cheese balls are made.

Ha! This actually is how "spherified"[1] foods are made.

[1]: http://www.molecularrecipes.com/spherification/basic-spherif...

The article does not list Saint Jacques Tower in Paris. http://en.wikipedia.org/wiki/Saint-Jacques_Tower

Perhaps because it was not built for the purpose of producing shot...

Interesting. And here I thought they were all made by hand. I guess shot producers aren't nearly the highly patient and dextrous craftsmen that I made them out to be.

Even the casting of lead bullets doesn't require all that much dexterity from what I've read. From memory (never had done this myself), you have a mold that hinges in half, you get it hot enough, close it and pour a molten lead based alloy into the sprues (generally 2 bullets to a mold?), let it cool down a bit, open the mold and knock out the two bullets, repeat.

Skill, but not a great deal if it, is definitely involved, and of course patience as you make then two by two.

Shot, on the other hand ... well, my family has been reloading shot shells since the '70s or earlier (my father has casks of Hercules smokeless powder from plus or minus WWII that he's still using), and the regular charge of shot for a 12 gauge shell is 1 oz plus or minus a little. So let's go for the reasonable worst case, dove, which are as about as small a game bird as is practical, and they require a lot more shooting at than the bigger birds because you generally conceal yourself in a location between sources of food and water, so you've leading them in a way which is particularly difficult.

A single 1 oz load would be 337 pellets of #8 shot. It's usual to go through more than one box of 25 per season ... so, oh boy, would that require "highly patient and dextrous craftsmen", and this activity of both sport and procuring tasty animals would be way beyond the reach of the working class.

(Math is fun.)

In my recollection, this is one in Austin, TX:


I may be wrong though. I wasn't able to find any references about it easily.


I can't find a tall tower anywhere near your marker though.

There it is!

There's quite a big and famous one in Baltimore that's right in the middle of town and hard to miss. And it's open for tours.


Is terminal velocity a factor in achieving a spherical shape? Is that part of the reason for the height of the tower, or is it just cooling time?

It sounds like cooling time, from the article: "Shot towers were replaced by the "wind tower" method by the end of the 19th century, which used a blast of cold air to dramatically shorten the drop necessary."


I think a falling ball of lead would have a very high terminal velocity, as it is quite dense and in a rounded shape. I doubt it has much of an effect at the height needed to make these shots.

About 90 m/s, depending on elevation.

Just last week I string to think how I'd make ball bearings and this strategy came to mind. Neat to see that it's actually feasible.

(Although bearings are made cold. See https://news.ycombinator.com/item?id=6374786 )

In Montreal a shot tower was kept when converting an old industrial complex to high-end residential units. Result is pretty good and made me learn about shot towers before reading it here: http://goo.gl/maps/WJZPj

Now this seems like it would have been a legitimate use for patents at the time!

The Dubuque shot tower is in my hometown. It's a really great piece of history but a shame that the site isn't more kept like the rest of the riverfront.

In the most restrained and calm way possible, I'm wondering why this is on Hacker News at the moment...

A Wikipedia article, concerning a technology that is effectively ancient and indisputably outdated, seemingly with no relevance to any recent events in the tech world, or the greater world in 2013 for that matter.

Occasionally it seems as if one could do "Random" Wikipedia click [0], find something marginally interesting, and post it here. It's strange that this would be the case, but I suppose the points voted on suggest that the community is interested in the subject. Don't get me wrong, I read the article and found it interesting, just to learn a little something new about history, but I then wondered how it could possibly relate to HN, and I went back to re-read before commenting as I was certain I must've been missing something regarding how this article relates to some current event / technology.

Edit 10:42EST, to restate the purpose as it seems people neglect to realize I too found it interesting and are saying "but it's interesting, I personally enjoyed it", please see the below sentence (Copied from above paragraph for clarity). This comment wasn't about personal interest, it's a question of relevance.


Don't get me wrong, I read the article and found it interesting, just to learn a little something new about history, but I then wondered how it could possibly relate to HN, and I went back to re-read before commenting as I was certain I must've been missing something regarding how this article relates to some current event / technology.


Ninja Edit: Note! The following will direct you to a random wikipedia page, may be NSFW. Follow at your own risk.

[0] http://en.wikipedia.org/wiki/Special:Random

In a most restrained and calm way I must also point out that the Guidelines have this to say about What to Submit:

  On-Topic: Anything that good hackers would find interesting.

  anything that gratifies one's intellectual curiosity.
and they also say this about complaining about submissions in comments:

  Please don't submit comments complaining that a submission
  is inappropriate for the site. 
They are silent about pointing out the guidelines in comments on comments that complain about submissions.


I'll take it over another self important blogger's take on the NSA. I found the article to be interesting and enjoyed it.

This kind of stuff is actually why I come to HN. I'm not really interesting in reading Blogger-25981875's take on <insert scandal>, and definitely not "I became an entrepreneur and if you do exactly what I did you can be successful too".

While it may not be news, and it may not be immediately useful or directly applicable, I found this a fascinating process, and a good illustration how something very simple can be a very effective solution.

Side (but on-topic) note: I don't necessarily agree that building a 49 m tower to make tiny shot balls is "a very effective solution".

It is if you're making huge amounts of them and you're in the 19th century.

See here https://news.ycombinator.com/item?id=6374682 where I calculate a "single 1 oz load [for dove] would be 337 pellets of #8 shot"

Now, way back when they were probably more using larger sized shot for larger birds (dove are about as small as is practical, and probably more useful for learning real wing shooting), but that gives you an idea of the scale. If you go up to #6 for pheasant and grouse sized birds, 1 oz is 219 pellets.

And, yeah, this is a very cool hack for cheaply making this stuff, which we do indeed use in mass quantities.

It's conceptually simple and produced great results. I agree that it might not be the most effective solution there is, but it seems like it was the most effective at the time (which is why they were used).

Perhaps you mean efficient rather than effective? It does seem to be quite effective, despite the superficially amusing fact that a very tall tower is being used to form a very small product.

Though whether it's inefficient in any other sense is, I think, open to question: The up front expense and difficulty of the tower is a one-time cost, and I'd think maintenance on it would be fairly minimal. I'd think other methods discussed in these comments would almost certainly incur significantly more overhead, particularly over the life of the facility.

> Perhaps you mean efficient rather than effective?

Parent said "very effective", I am not sure what it means if not "efficient".

> Though whether it's inefficient in any other sense is, I think, open to question

Indeed, that's exactly what I meant.

Just out of interest:

1) Why, exactly, should this not be on HN?

2) What makes a submission suitable to be on HN?

You've said that you found it interesting. You maybe learned something? Your curiosity isn't piqued - do we still use this process, does anyone anywhere in the world use this process, could it be used for anything, what happens if you use other materials or if the air is hotter or colder, or if we try it on the moon or on Mars or etc etc etc?

Why not Hn. It is an elegant solution to a manufacturing problem, im sure many of you ask how it can be done more effectively requiring less space and material.

It's on Hacker News because 170+ people decided it should be.

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