Determining Thread Length Engagement for Optimal Boss Length

In summary, determining the appropriate thread length engagement is crucial for achieving optimal boss length in mechanical fasteners. This requires considering various factors such as material properties, thread type, and application requirements. A balance must be struck between ensuring a strong and secure connection while avoiding excessive stress and potential failure. Accurate calculations and proper testing are essential for determining the ideal thread length engagement for a specific situation.
  • #1

Please help me in finding thread length engagement.

Please find attaché image

I have a product comprising of 2 parts fastened together.
Hydraulic fluid is passing thru it.

My inputs- load, size of the fastener used (ex: M8 X 1.5).
My constraints are-the boss length should be kept to the minimum (because of assembly constraints.

I need to find the minimum thread length engagement of the threads i.e. whether it can sustain the load when only 5 full threads are engaged or more threads need to be engaged.
By finding the engagement length I can decide the length of the boss.

In the process visited the site

In the formula the load parameter is not considered.

Please mail me a solution.


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  • #2
Oy. This has me worried.

First off, the calculations you see do not require a load because they are based on years of tests and empirical evidence. They are assuming failure in either shear, tensile or combined loading. Also, the class of tolerances on the threads will have an effect on the final number as well. One big thing to consider is the difference in materials between the external thread member and the internal thread member.

I would highly recommend getting a copy of FED-STD-H28 to get a background before attempting to do these calculations. An even better item for you to get your hands on would be SAE paper 770420, Analysis and Design of Threaded Assemblies.

What kind of pressures are you dealing with? Hydraulic fluid implies that it will be high pressure, but it could be on the return side which is usually pretty low pressure. I also didn't see any face seals between the passages. Is this a complete drawing or is this just to illustrate what you are doing with the fasteners?
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  • #3
I'm not really sure why you're adding the tabs for screwing the two parts together. I doubt this is for heat exchanger design, but typically, reservoirs, heat exchangers, etc are all BRAZED together. I would recommend you investigate this as an option - it can usually handle fairly high burst and proof pressures.
  • #4
Thank you

Related to Determining Thread Length Engagement for Optimal Boss Length

What is thread length engagement?

Thread length engagement is the amount of thread that is in contact between two mating parts in a threaded assembly. It is important for ensuring the strength and stability of the connection.

Why is thread length engagement important?

Thread length engagement is important for several reasons. It helps to distribute the load evenly between the two parts, prevents loosening or stripping of the threads, and provides a secure and stable connection.

How is thread length engagement measured?

Thread length engagement is typically measured in terms of the number of threads that are in contact between the two parts. This can be measured using thread gauges or by counting the number of threads that are visible on the assembled parts.

What is the recommended thread length engagement for different types of connections?

The recommended thread length engagement can vary depending on the type of connection and the materials being used. Generally, a minimum of 1-2 full threads should be engaged for a secure connection. For softer materials, a longer engagement may be necessary.

What are the consequences of insufficient thread length engagement?

Insufficient thread length engagement can result in a weak connection that is prone to loosening or failure. It can also lead to stripped or damaged threads, which may require replacement of the parts. In critical applications, it is important to ensure that the thread length engagement meets recommended guidelines for safety and reliability.

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