25 votes
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How do vending machines prevent people from stealing goods?

The vending machines have different product delivery box implementations. One of the most common ones -I've encountered- is the following: Basically you have a box which has an opening, as shown in ...
NMech's user avatar
  • 24.3k
20 votes

Aluminum weight saving

I believe it has less to do with strength and more to do with stiffness. A rod of aluminum of the same length and weight as a a steel rod will be just as strong (force required to break) but have ...
DKNguyen's user avatar
  • 5,496
12 votes

How do vending machines prevent people from stealing goods?

I think the locking mechanism is more or less like this: Note, the actual setup could be different but the concept of locking through a barrier that prevents the slide plate been pushed up remains ...
r13's user avatar
  • 8,174
9 votes

Aluminum weight saving

TL;DR: Materials perform differently under different loading conditions. Some applications are more suited for steel others for aluminium I will try to give another more general perspective/approach, ...
NMech's user avatar
  • 24.3k
6 votes
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What is this strange nut and what to do with it

The image shows what is often known as a zerk fitting, aka a grease fitting. The ball seals the passage from the outside to the internals which require grease. A grease gun with a properly sized ...
fred_dot_u's user avatar
  • 7,055
6 votes

What is "reversal" in mechanical engineering drawing?

It approximately means it is allowed or forbidden to have scratches at the place of round. When you are making cylinder surface you can to do it many different ways: milling, welding, soldering. In ...
Andrew Kachalin's user avatar
6 votes

Aluminum weight saving

Sometimes the strength isn't required, so size for size, aluminium is lighter. e.g. bicycles often use aluminium screws to hold the bottle cage to the frame. The size of the screw is set to be ...
Jonathan R Swift's user avatar
6 votes
Accepted

Is it essential for two meshing gears to have even number of teeth?

The recommendation is quite the opposite. The teeth of meshing gears are, where possible, chosen to be odd or, better again, primes so that a bad tooth doesn't keep hitting the same point on the ...
Transistor's user avatar
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5 votes
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What does it mean for a machine design to be "kinematic"?

I think it might be shorthand for a kinematically constrained design. It is the ...
Frodyne's user avatar
  • 166
5 votes

Where water goes in split air conditioner system in "dry" mode?

Split system air conditions (heat pumps) are refrigerator based systems. The two tubes you mention transport refrigerant from the compressor in the outdoor to unit to the indoor unit & return it ...
Fred's user avatar
  • 9,667
5 votes

Why actuators are mounted in inverted position?

The cylinder will be mounted where it is easiest to get the hydraulic lines to it.
Tiger Guy's user avatar
  • 6,793
4 votes
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Shape of the shaft of knurling device

Yes, it would be easier to drill the hole but there are other reasons. It's makes the shaft the same width as the red bearing also clamped by the green sides. The shaft will experience torque when ...
Transistor's user avatar
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4 votes
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Why one big cargo ship is more efficient than 10 or 100 smaller ships?

Regarding the first question: why 1 ship is more efficient that 100 smaller ones. if you did some research I'm sure you'd find that one large ship probably uses about the same steel than a 10 smaller ...
NMech's user avatar
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4 votes

What mechanism is available to rotate a metal piece on another metal piece?

You have the right idea using a shoulder screw. In between the two pieces, use flat washers and a springy Belleville washer. A Belleville washer, also known as a coned-disc spring, conical spring ...
Mike Waters's user avatar
4 votes

What is "reversal" in mechanical engineering drawing?

Imagine you were driving a car along the path shown in a cross section view of the radius - you need to make a 90 degree bend, and you need to stay inside the cones that denote the tolerance band. In ...
Jonathan R Swift's user avatar
4 votes

Aluminum weight saving

When Zeppelins were designed, only non-sparking materials were allowed for them so the hydrogen gas that invariably seeps from the gas bags would not find an ignition source. Steel did not qualify. ...
Peter Kämpf's user avatar
4 votes

Can stainless steel be used in continuous high temperature environment (500°C to 850°C)

Most grades of stainless steel can handle 850 degrees without problem. Even the cheap ones such as 304. Although at that temperature it will be glowing bright red. It will discolor and some ...
August Rabe's user avatar
4 votes
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Unable to understand minimum length of engagement for bolts

The minimum length of engagement ist the length of engagement that (computationally) will ensure that overtightening the screw will snap the screw, and not strip the threads. The external and internal ...
bukwyrm's user avatar
  • 186
3 votes
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Adding the effects of two rods to move a single rod

If I hadn't messed up understanding your idea then you can connect all rods to achieve the desired result. I've considered two bars connecting to maintain all rods paralel to each other. The starting ...
Leafk's user avatar
  • 345
3 votes

Bending moment when there are no constraints

The impulse causes lateral acceleration of the rod and rotation of the rod. $$ P=m\frac{dv}{dt} \quad \text{for lateral acceleration}$$ $$ P=I\frac{d\omega}{dt} \quad \text{for rotational acceleration}...
kamran's user avatar
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3 votes
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visualization of intersection of two objects

I don't want to spoil the fun of solving this for yourself so I offer the following suggestions: Redraw the assembly with all edges, including the hidden edges, shown as dotted lines. Draw solid ...
Transistor's user avatar
  • 10.6k
3 votes

Mechanical Engineering: How To Amplify Kinetic Energy In Axial Rotational Gear Machinery?

A simple machine is what you're referring to. A simple machine turns motion into mechanical advantage. Examples include: lever inclined plane pulleys wheel & axle gears inclined plane/wedge/...
Tiger Guy's user avatar
  • 6,793
3 votes

Aluminum weight saving

And, in addition for sheet metal application like aircraft skin the aluminum could be 0.040 " ( 1 mm) thick ; the equal steel would be 0.013" thick . The steel would be so thin it would ...
blacksmith37's user avatar
  • 6,134
3 votes

Aluminum weight saving

Some engineering aspects, related to designing end products (my experience is in prototypes and small-volume production): Machining costs (accounting for time and tool wear when milling/turning) are ...
Chris H's user avatar
  • 396
3 votes
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What technology is behind a deep freezer door

On a different scale and with different and more severe temperature variations, consider the following: Place a few ounces/tens of milliliters of water in a plastic bottle. Heat it to boiling in a ...
fred_dot_u's user avatar
  • 7,055
3 votes
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Cam-operated clamps: When are logarithmic cams preferred and when are involute cams preferred?

if an involute of a circle is turned uniformly around its center, then the tangents to the involute move in a uniform translation motion. the mechanical advantage is greater when the gap is just below ...
Tony Stewart EE75's user avatar
3 votes
Accepted

What is the advantage of "carriage"-style bearings for telescope domes, lighthouse lenses etc.?

The big advantage is that there is very little load on the axles (other than the carrier ring) and therefore there is almost no wheel-axle friction. Why not fix the wheels to the object that is being ...
Transistor's user avatar
  • 10.6k
3 votes
Accepted

Infinite life of a material, Fatigue Strength

Studies on fatigue life estimations was first done on steel axis in trains and continued on for other steel constructions. The majority of the fatigue publications have been based on fatigue ...
loStraniero's user avatar
3 votes
Accepted

How do mechanical engineers, in practice, account for drag/air resistance when designing machines?

In many cases, probably a majority, they ignore air drag, and simply design the torque capability of the engine as enough to deliver the required output, plus some sizable margin to overcome sources ...
RC_23's user avatar
  • 831
3 votes

I am looking to make thread changes to a handpiece for laser hair removal equipment

Looking at a the bottle cap of a 1/2 gallon plastic (blow molded) milk jug, for inspiration. Is skinny, and happens to have a triple-start thread like yours. So maybe the triple-start thread is a good ...
Pete W's user avatar
  • 1,526

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