How Do You Calculate the Required Torque for a Square Threaded Screw?

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In summary: So Q is 47.25*0.94 = 41.875 ft lbs.You could calculate this by taking the bolt diameter and multiplying by .9 and then dividing by 12. So, if the bolt is 3 in. in diameter, Q would be 312.5 ft lbs.
  • #1
stinlin
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Square threaded screws...

Homework Statement


http://img180.imageshack.us/img180/6789/statics2kq3.gif

Picture ^^

High-strength bolts are used in the construction of many steel structures. For a 1-in.-nominal-diameter bolt the required minimum bolt tension is 47.25 kips. Assuming the coefficient of friction to be 0.35, determine the required couple that should be applied to the bolt and nut. The mean diameter of the thread is 0.94 in., and the lead is 0.125 in. Neglect friction between the nut and washer, and assume the bolt to be square-threaded.


Homework Equations



tan(theta) = L/2*pi*r
Q = M/r


The Attempt at a Solution



All I was able to figure out is that...well, I wasn't. I tried drawing some pictures, but my big source of confusion is that I don't know how to draw a diagram for the thread and where the numbers all go. :( Please give me an umph in the right direction!
 
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  • #2
The threads on most bolts and nuts are triangular in cross-section. Is your instructor trying to simplify thing for you a bit by assuming that the cross-section of the threads are rectangular and not triangular? If so, can this help you?
 
  • #3
This is an introductory statics class, so we do square-threaded screws for now. The problem that I'm having is that I don't know how to address the bolt tension and what that does and how it affects this couple I need to find. The answer is given to be 737 lb*ft.
 
  • #4
Is this a legit diagram, with T being the bolt tension? Then I could solve for Q and get some large number, multiply it by the diameter of the bolt and divide by 12 to get into feet, right?

If so, why do I use the bolt diameter and not the 1 in. diameter?
 

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  • #5
turbo-1 said:
The threads on most bolts and nuts are triangular in cross-section. Is your instructor trying to simplify thing for you a bit by assuming that the cross-section of the threads are rectangular and not triangular? If so, can this help you?

Check out Acme threads. They are almost square in section.
 
  • #6
Your diagram is the right idea. Imagine you have a piece of paper wrapped round the bolt and draw the thread on it. Then unwrap the paper and you will get something like your diagram, where the thread is an inclined plane.

The numbers you were given mean the diameter of the unthreaded part is 1 in. That's the part where the tension has to be 47.25. The mean diameter of the thread (half way between the outside and the base of the thread) is 0.94. That's the radius where the force from the nut is applied and converted into a torque.
 

1. What is a square threaded screw and how does it differ from other types of screws?

A square threaded screw is a type of fastener that has a square-shaped thread instead of the traditional V-shaped thread found on most screws. This type of screw is designed to provide increased strength and resistance to stripping compared to other screw designs.

2. What are the advantages of using square threaded screws?

Square threaded screws have a higher load capacity, meaning they can withstand heavier loads and torque without breaking or stripping. They are also less likely to loosen over time, making them ideal for applications where vibration or movement is a concern.

3. Where are square threaded screws commonly used?

Square threaded screws are often used in heavy-duty applications where high strength and resistance to stripping are required, such as in machinery, construction, and automotive industries. They can also be found in furniture assembly and other household items.

4. How do you install a square threaded screw?

The installation process for a square threaded screw is similar to that of a traditional screw. You will need a screwdriver or power drill with a square drive bit to turn the screw into the material. It is important to make sure the screw is aligned properly and not cross-threaded to avoid damaging the threads.

5. Can square threaded screws be used with other types of screws?

While square threaded screws are designed to be used with corresponding nuts or threaded holes, they can also be used in combination with other types of screws. However, this may affect the overall strength and performance of the fastening system, so it is important to consult with a professional before doing so.

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