torque vs thread engagement

[muzaffaralkaff]

Hi all, Im new engineer working in a automotive industry. I would like to ask something about torque vs thread engagement. Here I enclosed a picture for you to more understanding about the problem. Torque allowed for this this nut to tighten is 2.5kgf ~ 3.5kgf (24.5Nm ~ 29.5Nm). What is possible thing to be if the torque applied over than this spec? And how to control the clearance between the bush and the shaft so when the torque apply and the part moving, the bush not easy to wear? TQ.

[JAlberts]

As to your first question, generally the thread engagement length and component materials are designed such as to result in a tensile stress failure at the root diameter of the inner thread in the event of torque overloading.

As to your second question, I am unclear as to which component in the drawing is the "shaft". Is it the brown colored tubular component?

[Kelly_Bramble]

Look at the following thread engagement calculators:

http://www.engineersedge.com/calcula...shear-area.htm

http://www.engineersedge.com/calcula...engagement.htm

http://www.engineersedge.com/calcula...engagement.htm

http://www.engineersedge.com/thread_stress_area_b.htm

http://www.engineersedge.com/thread_stress_area_a.htm

[muzaffaralkaff]

yes ,the shaft is the brown colour tubular component.

[JAlberts]

In that case, if you intend to have free rotation between the shaft and bushings then your dimensioning tolerances of the the shaft OD and bushings' ID appear to be the reverse of what it should be. With the current tolerancing the max OD of the bushings is 17+.3 = 17.3 and the minimum ID of the shaft bore is 17-.3 = 16.7 which will result in an .6 interference between the shaft ID and bushings OD.

Also in this case you need to carefully analyze the worst case stack up dimensions and tolerances of the bushings' flange thickness plus the material thickness of the two housing walls plus the the bolt head to shoulder length to insure that there will be end clearance between the bushing flanges and the shaft ends at the shafts maximum allowable length.