Questions tagged [mechanical-engineering]

Questions within the problem domain of mechanical engineering. Mechanical Engineering can be a broad field; consider choosing more specific tags if they apply.

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7
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2answers
987 views

What is the difference between using separate lathe and mill or a combination machine?

I'm interested in metalworking as a hobby, to make small parts for my numerous other hobbies. I'm looking at those cheap, typically Chinese import mini-lathes and mini-mills. I've read about their ...
7
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2answers
212 views

Cutting mechanism for a robot in confined spaces

I'd like to build an exploratory robot that can fit within confined spaces1. As the robot moves along the inside of a 4" pipe, it's likely to encounter some obstacles that need to be removed. ...
7
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2answers
773 views

How efficient are jet engine thrust reversers?

Most reasonably sized commercial aircraft rely on jet engines for propulsion. Upon landing these aircraft use a number of means to come to a stop with the two most important being (I believe) ...
7
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3answers
12k views

Force required to empty a syringe

How would you go about solving the following problem. I believe Bernoulli's equation needs to be employed, but I'm not sure how. Find the magnitude of the force that needs to be applied to a piston ...
7
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4answers
6k views

Switching batteries from series to parallel - technical solution

I'm thinking of developing a pocket 'power bank' that could provide both 6V and 12V - a charger to charge either a phone (with 6V) or a notebook computer (with 12V). The electrical diagram is simple ...
7
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1answer
859 views

What are the benefits of a diaphragm pump vs a simplex pump?

What are the benefits of a diaphragm pump over a simplex pump? Is there any specific design criteria that should be used/stated in an engineering specification for a diaphragm pump?
7
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1answer
249 views

Is it possible to replicate a Tesla valve in large scale?

Supposedly a Tesla valve will impede fluid or air flow in one direction whilst allowing flow to move freely through the valve entering from the opposite direction, without using any moving parts. Also ...
7
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1answer
2k views

Force in a crank system

Statement In a crank system, as described in the picture, we know the values of: the width of the connecting rod ($m$), the width of the crank ($b$), the torque in the crank ($M$) and the angular ...
7
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1answer
671 views

Are smaller heat-pumps more efficient?

I was a doing a placement at a company, and they were designing a new heat pump. I was told the more compact you can make a heat-pump, the better it is for efficiency, and they mentioned something ...
7
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1answer
605 views

One large fireplace flue versus two smaller ones

I am a mason contractor whom specializes in Rumford Fireplaces. I am helping design a fireplace that had a problem fitting in a single 18" x 18" flue pipe. So I installed two 13" x 13" pipes adjacent ...
7
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1answer
2k views

Is there a relation between porosity and PPI density in porous media?

I've seen two methods to describe porosity of porous media (specifically metal foams): Porosity $\epsilon$ which is a ratio between volume of voids and total volume of the medium. PPI (Pores Per Inch)...
7
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1answer
801 views

Calculating the ultimate achievable vacuum pressure of a diaphragm pump

I am looking to design a diaphragm pump for a device. I know that I would need to achieve a (negative) vacuum pressure of ~ 350-400 mmHg. I know from standard rotary pump design the pump rate should ...
7
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1answer
1k views

What is the name of this mechanism for raising and lowering the impression cylinder of a printing press?

It is like a cam that has an off-center hole, and it rotates in its fixture with a knob to lock it in place. The purpose is that you can loosen the knob and rotate the piece to slightly raise and ...
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2answers
1k views

How can I model or simulate motion caused by an internal vibrating motor?

I have a vibration motor contained in an object. The motor looks similar to this: When the motor is running, I want to simulate the movement of the container object that results from the vibration of ...
7
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1answer
5k views

Why ductile materials fail in shear when subjected to torsion?

I was reading the book Mechanics of Materials by Beer and Johnston.The author points out in torsion chapter that ductile materials generally fail in shear.And brittle materials materials are weaker in ...
7
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1answer
3k views

Principle of Virtual Work vs Castigliano's (Second) Theorem

I had a look online and into some literature however I did not seem to find a good comparison for the two different methods. They are both used for determining displacements and slopes (rotation by ...
7
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2answers
1k views

Writing a filtered derivative term of the PID controller into the C++ code

Everywhere I look, be it a PID, lead, lag control or anything else, there are Simulink schematics with transfer functions. This is all nice for system response simulation, however currently I have to ...
7
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1answer
385 views

Energy of a 3D Timoshenko beam

I am interested in the kinetic energy T and the potential energy U of a three dimensional Timoshenko beam. For a 2D Timoshenko beam the energies read: $$ T = \dfrac{1}{2} \int\limits_o^l \left( \rho ...
7
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2answers
992 views

How does a compressor know to lower condensing pressure in chiller?

I am working on an indirect ammonia chiller that is used to cool the ice in an arena. The system consists of 3 reciprocating compressors, an evaporative condenser with a vfd on the fan, a float ...
6
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3answers
6k views

Why are nuts 6-sided?

Why are nuts 6-sided? Why not 4 or 8?
6
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3answers
2k views

This device is used in washing machines to dispense water and cleaning solution in the right amounts. What is the working principal of it?

The following device is generally used in washing machines to dispense water and cleaning solution in the right amounts whenever needed. How does this device work?
6
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4answers
3k views

What is the maximum angle of a shelf angled brace?

So suppose I want to make a single shelf protruding from a wall and to place a heavy object on it (Figure 1). A shelf like this would fail (assuming no internal mounting that penetrates into the wall)....
6
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5answers
23k views

What is Starting Torque?

I'm having a hard time finding an answer from the internet. What does starting torque mean?
6
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4answers
4k views

Is a circle the strongest 2D shape for containing internal pressure?

I understand how a circle (or sphere if you want 3D) is the best shape for holding a vacuum inside a container, but what if you wanted to have a large positive pressure inside of the container instead ...
6
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4answers
3k views

What is the use of gears in a device with a fixed gear ratio?

From my understanding, there are two uses of a gearing system: to change the speed of output rotation (trading it with torque), and to change the axis of rotation. Now, in a car, for example, it is ...
6
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2answers
16k views

Why use a 'dogbone' shape for tensile testing specimens?

Why is that the shape of the tension test specimen a dogbone-like shape? I know that it is so that the deformation is confined to the narrow center region and to reduce the likelihood of fracture to ...
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6answers
3k views

Why are turbo compound engines not more widely used?

Turbo compound engines extract some exhaust energy by using it to power a turbine connected to the driveshaft. Why are these engines not more widely used?
6
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2answers
219 views

Is it safe to drop a bomb?

I realise that "bomb" can refer to all sorts explosives, but I am mainly interested in air-dropped bombs. Ever since reading about the USS Forrestal fire, I wondered about the safety of bombs when ...
6
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2answers
5k views

Does having 2 engines together increase anything?

If I have a vehicle (V1) with one 100 kW engine and an identical vehicle (V2) with 2 of these 100 kW engines, will this mean that V2 will have double the torque of V1 and double the top speed of V1? ...
6
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2answers
165 views

Shape of chain saw teeth

Looking at the teeth of a chain saw, I believe the chain moves from right to left while cutting. It has two wedges A and B. I've never owned a chain saw, so I've been trying to visualize how these ...
6
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3answers
1k views

Mounting and Coupling an Encoder

I was wondering how to mount a small rotary encoder to a platform in order to measure how far a small treaded robot has traveled. We're using this tread/wheel set: We've tried epoxying the encoder ...
6
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1answer
414 views

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

I kind of have an intuition or at least imagination about how fillet|chamfer of inner edges|vertexes reduce stress (concentration). But does that apply to outer edges|vertexes aswell? Maybe to a ...
6
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3answers
570 views

How do you make a 3D print with an accurately aligned bore hole?

I am printing a wheel with a 2.5mm hole in the middle to accept a shaft of a motor with a set screw. The problem I am having is that the wheel is always wobbly when spinning (sometimes more, sometimes ...
6
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3answers
2k views

How do I calculate the max flow rate for a pump with no power restrictions?

Let's assume we have a pump and it can draw as much power as it needs. As the pump speeds up, it creates vacuum in the intake. At some point it draws the gas/liquid so fast, the intake pressure is so ...
6
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4answers
1k views

Is it possible to fire a ball of water that holds its shape?

Background I participate every year in a huge water balloon battle. The clash happens between two universities so you can imagine that the commitment, at least for some people, is quite high. To give ...
6
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2answers
170 views

Force Balance Question

Hello, I've been asked to show that: $$d\Gamma=\tau 2\pi r^2 dr$$ Where $\Gamma$ is the torque applied to the shaft and $\tau$ is the shear stress of the sample fluid at radius $dr$. So, I know that $...
6
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3answers
1k views

What do you call a mechanism where rotation is transfered in one direction only?

I have the following to wheels that rotate on the same axis: Assuming that they are stuck together, if I rotate the green one the red one rotates at the same speed and when I stop the green one the ...
6
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5answers
985 views

Ways to brake an axle

I am currently studying Mechanical Engineering and am doing an assignment where I have to design a wire rope tensioner where a wire rope is unspooled from a drum, but the wire has to be at a specific ...
6
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3answers
1k views

How Much Efficiency is Lost in a Gear Train

I want to get a rough estimate for the transmission efficiency of two different gear trains. One is a one-stage gear train with 11.67:1 ratio (140/12 teeth) and the other is a compound two-stage gear ...
6
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4answers
30k views

How to define Knurl on drawing?

I made this kind of knurl on shaft : but I am not sure how to be define on the drawing. I found some examples but not sure if they are correct. On the examples there type (GV) and depth of knurl and ...
6
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3answers
159 views

Is this Square Track Cam valid?

I want to convert rotary motion (the orange propeller) onto a square path (the dark gray path). Is this a valid way to go about it? Would it be possible to use a square peg instead of a round one (the ...
6
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1answer
412 views

Convergent-Divergent Nozzle Design from Exhaust Velocity

I'm working on designing a Cold Spray system that uses a convergent-divergent nozzle to achieve a 800 m/s exhaust velocity. I'm assuming 400 psi nitrogen at room temperature is provided at the inlet ...
6
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2answers
4k views

Snap-fit design

I'm designing 2 objects that should be attached to each other and removed when it's necessary. So I though about snap-fit as a solution. There is a lot of types of snap-fit but I'm planing to use a ...
6
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2answers
1k views

Are jeweled bearings commonly used for applications other than mechanical timepieces?

Jeweled bearings use a metal spindle with a jewel lined pivot hole (pictured below). They have been important in the manufacture of mechanical timepieces since the early 1700's. Their importance ...
6
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3answers
2k views

What is the difference between fault tolerance and robustness of a system?

I am trying to understand the difference in the definition of "fault tolerance" and "robustness" when it comes to system design. For instance, what would be the main design ...
6
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2answers
1k views

Why does AN-94 have higher burst fire than its cyclic rate?

AN-94 is an assault rifle of Russian design chambered in 5.45 caliber. It is claimed to be state-of-art in Russian small arms development. The most important design differences (relative to common ...
6
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3answers
1k views

How to manufacture cutting dies for metal foil?

I am making a die for cutting arbitrary shapes from thin (0.1–0.5 mm) copper foil/sheet using a manual arbour press. The product will be an oak leaf shape, approximately life-size, for use as part of ...
6
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2answers
1k views

How to drill larger bore in pipe?

I am trying to bore out a red brass pipe from 3/8" to 10mm using my drill press and a standard twist HSS bit. Running the drill at 600rpm I can't get more than half an inch in before the drill starts ...
6
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2answers
766 views

How can I finish a round hole so it has 90 degree corners (flat bottom)?

I have a 10 mm depth x 5 cm length 99% Tungsten rod. How can I machine the described hole so that instead of having a bevel from the tip of the main drill-hole bit, it has a perfect 90 degree corner ...
6
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2answers
499 views

What is the Boussinesq approach?

I want to simulate a turbine in Fluent. For this reason, I studied some papers. In these papers, Turbulence is modeled using the realizable k–e model and Non-equilibrium wall functions are used in the ...

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