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54 votes
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Why are railroad tank cars bent in the middle?

As other have pointed out, the main utility is to allow easier cleaning of the tank cars from sediment (solid precipitates). Usually, there is a drain in the lowest point. The reason that it is in ...
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35 votes

Why does this fence have a kink?

They're V-Mesh panels. V-Mesh panel from Irish Wire. The offset of the vee gives rigidity in the horizontal direction. The vertical rigidity is addressed by the fence posts. It's available in 2, 3 or ...
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25 votes
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From an engineering standpoint, what is the purpose of the indent in a coffee lid?

From the "Solo Traveler" patent: A more specific object of the present invention is to provide a lid having an opening formed therethrough to enable drinking, and having a recess formed in the lid ...
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23 votes
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Why are three way bridges rare?

Most bridges (and overpasses) are built to cross over something. With a few notable exceptions, most of these "somethings" are relatively long perpendicular to the desired crossing direction and ...
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20 votes

Why don't motorcycles have as good a turning radius as bicycles?

The simplest answer to the question is "because the motorcycle gets in its own way" Take a look at this picture of a trials motorcycle; it has perhaps the smallest of turning circles ...
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17 votes
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Would a centrifugal flyweight governor system slow down the descent of an object that is free falling down to the Earth's surface? (Revised design)

Once the cylinder is released and starts to accelerate downward, the rotating flyweights should pivot upwards to a certain degree (as shown in the drawing) and should act as a drag on each of the ...
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16 votes

Why don't motorcycles have as good a turning radius as bicycles?

A bicycle usually weights about 18 pounds versus an average of 180 pounds for a motorcycle. In tight turns a bicycle can easily be controlled by the rider shifting their body's center of mass as ...
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14 votes

Is this dropout design as bad as I think?

An ideal dropout design would...... OK, already there you've gone into the weeds. There is no ideal dropout design. Engineering real world things is a balance of tradeoffs. You have to balance the ...
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13 votes
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Involute gear curve when root diameter falls below base diameter

In general, each tooth of an involute gear is made up of two curves: the involute curve and the root fillet. The involute curve is essential for gears to operate properly, and allows power to be ...
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13 votes
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SOLIDWORKS - 3D Sketch of Trombone

See the .gif below! EDIT: You may need to enable visibility of these handles if they're not on by default - it depends on your default profile/settings.
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13 votes

Why are railroad tank cars bent in the middle?

Same reason the Corsair fighter has bent wings. Makes clearances easier. Look at the lumpy, sticky-outy things on a tank car. You have the trucks/bogeys at the end bottom... and the massive fill ...
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12 votes

Why aren't screens round instead of rectangular?

The earliest CRT displays were in fact round. However, that was more due to manufacturing tradeoffs of making large glass envelopes with vacuum inside than a desire for the display area to be round. ...
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12 votes

Do outer fillets|chamfers also reduce stress as inner ones do?

Sorry for not taking your "Thin Hollow Brick-Shaped Object" as an example - I felt a standard notched test specimen would illustrate the principle more clearly: It can be seen that adding external ...
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12 votes
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Is it useful to stuff my glasses with newspaper to protect them?

In itself putting paper inside a glass will make very little difference. Glass is a brittle material and tends to fail by shock and point loading. Its static tensile strength is actually pretty good. ...
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12 votes
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How to work on big CAD project in team?

It's a massively important question. Short response: apply the concept of encapsulation. Divide into subsystems During development, assign design-ownership (distinct from project manager role, ...
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  • 1,367
10 votes

Why are railroad tank cars bent in the middle?

So any sediment will collect there as part of cleaning. Then other designs have a more pronounced bend to allow for the bogies and also keep the height down - some tunnels are lower.
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10 votes

Why does this fence have a kink?

Bending adds rigidity. Take a piece of paper, fold it, the bend gives it a rigid form to hold more weight. V-Mesh fences are also used in equestrianism as horse fencing helps keeps predators out and ...
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9 votes
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Why don't motorcycles have as good a turning radius as bicycles?

I'll approach this from a different perspective to the other answers: Pushbikes have no limits on the steering range because they don't need to add the complexity and weight. They're simple, light, ...
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8 votes
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Sending out a 12d Civil Design Model

Before I start, let me disclose that I don't know a lot about the details of infrastructure projects or your file format, but I think the general considerations are fairly universal. There are a ...
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  • 4,501
8 votes

Why are three way bridges rare?

Multi-way bridges are rare for river crossings for the reasons you describe; however, they are seen as a component of highway interchanges, usually when left entrances/exits are present or access ...
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8 votes

How to prevent algae in water cooled laser tubes?

I use polypropylene glycol in my CO2 laser tube under florescent lights and have not had any problems. It also comes with the added benefits of freeze protection and corrosion protection. If you ...
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  • 7,444
8 votes
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Why are spur gear ratios not always whole numbers in practice?

Gear ratios can be referred to as hunting and non-hunting ratios. In a non-hunting ratio, any one gear tooth will contact its corresponding gears' teeth in the same place every time. In a hunting ...
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  • 106
8 votes

Why do car-seats have an expiration date?

It's a combination of 1, 3, 4, the product development cycle, and the nature of the product. 1 - Damage in materials is a cumulative process, the product of hundreds or thousands of little events (e....
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  • 2,135
8 votes

Is it useful to stuff my glasses with newspaper to protect them?

Filling inside the cup with paper is just to lock in the wrapping of the same paper around the glass. It also offers coverage and protection of the rim of the glass. Because of the integrated, all-...
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7 votes
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Airflow selection mechanism

Are you bound to the shape/configuration of part you constructed in your question? If not, a simple 3-way pneumatic solenoid valve would make this very simple and leak proof(relatively speaking). They ...
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  • 1,578
7 votes

Why do microwaves get louder when the timer goes off?

When the timer reaches zero, the microwave tube is turned off. Depending on your house wiring, this large reduction in load may allow the line voltage to rise a bit. The fan, which continues to run ...
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7 votes
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What drives the honey dipper design?

Honey dippers work by using the viscosity of the liquid to raise a small amount of the liquid from a reservoir. Spoons work by trapping the small amount of liquid in a gravity well. Spoons therefore ...
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  • 11.2k
7 votes

Why raised face for mating parts?

In many cases, it's done for the sake of precision. As an example, an engine block is often sand cast. All mating surfaces in the casting master are made oversize, with the intention being that they ...
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