screw connect calculation

[Spoonful]

Hi all,

it might seem like a simple question, but it is the first time I come across it,?hope someone can help me on this.


here I have got a simple screw connection, say for example a rod one end with a female M10 socket , and another rod with male M10 at on end, then these male rod are screwed into the female rod, and there is a force F pulling the male rod out.

The known are the force F, rods to be machined from material with known material strength. I need to design the size of the thread, and length of engagement.

Any hints on this? Or any reference code or literature?

Thanks in advance.

Regards

Spoonful

 

[israelkk]

College mechanical design book such as from Shigley, Norton or Machinery's handbook

 

[leisure17]

base it on a standard nut & bolt

 

[Spoonful]

Any more specific comments?

 

[desertfox]

Try this site:-

http://www.roymech.co.uk/Useful_Tables/Screws/Thread_Calcs.html

 

[Tmoose]

If I was worried about the thread strength, then the transition in the male rod from thread outward would be of great concern too, for anything but strictly static loads. Unless a sculptured integral shoulder is scientifically tightened against the female socket the some portion of the threads are not protected by preload against dynamic loads.

 

[SnTMan]

Machinery's Handbook

 

[Cockroach]

You need to pull a more adequate reference than just the Machinist Handbook on this problem. How many ways can the thread fail? Answer that question and then do the computation for each case, pretty much this is the industry standard.

Failure by thread shear is a remote and impractical mode of failure given the shear area in the geometry. None-the-less, use the ASTM Specification for equations governing the phenonema. I would be more inclined to review normal and shear loads at the thread relief, notably the Pin, this is much more a real life possiblity for failure.

Alternately, you could pull the entire threading from the core of the material by shear. This is done at maximum torque specification of the thread, which is necessarily part of the calculation. Too often we as designers fail to specify the target torque for thread make-up, buddy grabs a snipe and wails on her until she breaks.

Hope this helps.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[Spoonful]

Thanks all for the reply, I did some research on this, I found normally, screw connection should fail at min. rod diameter, instead of thread stripping, by having a min. engagement length.

I remember someone used to tell me, if a screw connection would strip, the nut would strip before the screw. Is that about right?

 

[Cockroach]

No, the Pin (screw) would strip before the Box (nut). The thread shear area for the Pin is LESS than that of the Box, so for a given force, stress is greater on the Pin.

And this is always, regardless of Acme, Stub Acme, UN or otherwise straight thread configuration.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada