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Most probably, because manhole covers were/are made using cast iron, which were sand casted. Mold for sand casting is easily done in lathe (turning a wood on l
by achow 5y ago
Most probably, because manhole covers were/are made using cast iron, which were sand casted.
Mold for sand casting is easily done in lathe (turning a wood on lathe for precise shape is faster and more accurate than sawing).
So as one of the parent comment mentions - it is round because of production reasons.
- PinballWizard 5y agoMy take is because the manhole is round.
- achow 5y agoThe mouth of the 'hole' could be easily square, actually making a square shape is perhaps easier - since laying concrete is easier in straight lines. So, most probably the shape of the cast iron cover (circular), drove the shape of mouth of the hole.
- eecc 5y agoMy guess is it’s also a matter of practical usage: they’re made of heavy iron and a round one will fall in place whatever orientation it’s thrown over the cover, while a different shape needs to be carefully oriented. I suspect this also means less broken fingers.
- achow 5y agoBut round one is easier to steal.. just roll them off. Whereas a square or any such shape, would be very inconvenient to move. [Edit in response to a question] Some people have attempted to steal manhole covers in order to sell them for scrap metal. China Daily notes that there has also been a problem with taxi drivers removing manhole covers to "steal water and clean their vehicles". https://www.bbc.com/news/blogs-news-from-elsewhere-52400235 https://www.bbc.com/news/blogs-news-from-elsewhere-52400235
- adrianN 5y agoWhy would someone steal a manhole cover?
- xapata 5y agoTo sell them at the scrap yard. Gotta be careful driving in some countries; drive over an open manhole and you might crack an axle.
- takeda 5y agoIf Google is asking about them on an interview they must be important.
- rplnt 5y agoIt's a very common thing to steal. Lots of iron. That's why they use concrete-filled ones. That's why they are stamped so a scrapyard can be checked (or alert authorities).
- xapata 5y agoIf you're going around stealing covers, you're probably driving a truck and carrying them in the truck bed.
- bluedino 5y agoWho steals iron to turn in for scrap? It's only worth about 10 cents a lb. And then you have to haul it to the scrap yard. It's heavy! On the other hand, copper is $3/lb, brass $2/lb, aluminum is $0.50/lb
- pards 5y agoRead "Playing the Moldovans at Tennis". According to that book, most of the manhole covers had been stolen for scrap.
- varjag 5y agoIsn't as easy to shatter in handling too, lacking stress concentrators.
- discordance 5y ago... fell for it like a dude trying to get his try at opening a stuck jar lid.