Need guidance in thread design

In summary, the conversation discusses designing a thread/screw to induce a specific stress on an object and the application is similar to that of a threaded car jack. The person needs assistance with the thread design and asks for help from others who are familiar with it. Different resources and links are shared, and it is suggested to treat the thread as an inclined plane to calculate the stress and strain. It is also advised to use a thick piece of metal with a shallow pitch for better control and accuracy. Finally, the person expresses gratitude for the help received.
  • #1
bonzai
4
0
Hi all,
I would like to know how to design a thread/screw to induce a specific stress on an object. What I have in numerical data is the stress itself that is required.
The application is very similar to that of a threaded car jack. By turning the thread, it will lift up the load that was placed on the jack. In my case, what I have is a cylindrical structure with 4 threads (which I need to design) placed parallel and symmetrically around the cylinder. These threads will be strapped onto the cylinder so that by turning a nut on each of the threads, it will put the cylinder into tension and eventually stretch it apart.
I would like to know if anyone here is familiar with such thread design to get me started on this project.
I apologize for the poor explanation as it is quite difficult without a visual diagram.

Thank you!
 
Engineering news on Phys.org
  • #3
Thank you for the welcome,
I have actually browsed through the link you provided and it is still not clear to me as all I see are formulas.
To those familiar, correct me if I'm wrong but as I see from a machine design textbook, it seems to me I must use the equation stress = force / tensile stress area of the threaded rod. This is where I am a bit thrown off, so if I have the stress already and I want to find the tensile stress area in order to find the diameters of thread that I want, do I need to randomly select a value of force and keep iterating until I come to a certain thread diameter suitable for my application?
 
  • #4
I see what you mean now. I'm afraid that I know nothing about the subject. The best that I can think of is that you just treat the thread as an inclined plane and use whatever calculations are appropriate to that.
Your mention of having the thread "strapped on" to the cylinder really puzzles me.
Anyhow, I've about outlived my usefulness. I hope that someone else can be of more help. Meanwhile, perhaps the following can be of assistance in modeling your device:
http://www.thingiverse.com/thing:8793
 
  • #5
Thanks for the reply and model Danger.
Anyone else know how to design threads?
 
  • #6
What you are looking to design is basically what Instron (and similar companies) have designed. Stress and Strain go pretty well hand in hand, and what you are going to be doing is imparting a stress on the cylinder by way of strain. Really, all you need for this is the pitch of the thread so that you can determine how much rise you get per turn. if you get 2 mm per turn, you can determine how much strain you've imparted on the object and from that calculate the stress (more like estimate closely, since you'll need the modulus of elasticity).

Pick your thread diameter for well above the maximum stress the thing is expected to experience. You'll want to balance the size of the rod with the thread pitch angle. You want a nice thick piece of metal so it doesn't snap (and also because you don't want your stretching device to stretch itself! That would throw off everything) but you also want a shallow pitch so that you can control the accuracy of the strain being applied.

Edit:
These may help:
http://staff.fit.ac.cy/eng.la/AMEM316/MDESIGN%20Power%20Screw.pdf [Broken]
Link 2
 
Last edited by a moderator:
  • #7
That was of great help, thank you Travis King and Danger !
 

1. What are the key factors to consider when designing a thread?

When designing a thread, there are several key factors to consider. These include the material of the thread, the intended use of the thread, the desired strength and durability, and the thread's compatibility with other components it will be used with.

2. How do I determine the appropriate thread size and pitch for my project?

The appropriate thread size and pitch for your project will depend on several factors, including the type of material being used, the load and stress the thread will need to withstand, and any industry or international standards that may apply. It is best to consult a thread size and pitch chart or seek guidance from a professional to ensure the correct size and pitch are chosen.

3. What are the different types of thread profiles and when are they used?

There are several types of thread profiles, including V-thread, Acme thread, and square thread. V-thread is commonly used for fastening and sealing, Acme thread is used for heavy-duty applications, and square thread is often used in high-torque situations.

4. How can I ensure proper thread engagement and avoid stripping?

To ensure proper thread engagement and avoid stripping, it is important to use the correct size and pitch for your project, as well as high-quality materials. It is also important to properly lubricate the threads and avoid over-torquing the fastener. In addition, regularly inspecting the threads for wear or damage can help prevent stripping.

5. Are there any common mistakes to avoid when designing a thread?

One common mistake to avoid when designing a thread is not considering the load and stress the thread will need to withstand. It is also important to avoid using low-quality materials or incorrect thread sizes and pitches. Additionally, not properly lubricating the threads or over-torquing the fastener can lead to failure or stripping. Regularly inspecting and maintaining the threads is also crucial for preventing issues.

Similar threads

  • Sci-Fi Writing and World Building
2
Replies
52
Views
4K
  • Mechanical Engineering
Replies
5
Views
1K
  • Mechanical Engineering
Replies
4
Views
3K
Replies
2
Views
7K
  • General Engineering
Replies
1
Views
12K
  • Mechanical Engineering
Replies
10
Views
5K
  • STEM Academic Advising
Replies
2
Views
995
  • Mechanical Engineering
Replies
12
Views
9K
  • Mechanical Engineering
Replies
4
Views
1K
  • General Engineering
Replies
4
Views
17K
Back
Top