Thread torque
Thread torque
(OP)
Hi,
I need to calculate torque needed to tighten the bolt.
Problem is that the bolt and the hole are not of the same material, and the thread engagement length is fixed - usually smaller than recommended.
I just want to know is this right way to do it, or at least on the right track.
L - thread engagement length
P - thread pitch
D - outer diameter of the bolt
d2 - pitch diameter
u - thread coefficient of friction
us - bolt head-surface coefficient of friction
rs - effective radius of bolt head-surface connection
T - shear strength of the weaker material - ~0.6 of tensile strength
As = 0.5*pi*L*d2 - shear area
fi = atan(u/cos(30°))
ro = atan(P/d2*pi)
F = T_hole*As - shear force
T = F*(d2/2 * tan (fi+ro)+us*rs)
Thanks
I need to calculate torque needed to tighten the bolt.
Problem is that the bolt and the hole are not of the same material, and the thread engagement length is fixed - usually smaller than recommended.
I just want to know is this right way to do it, or at least on the right track.
L - thread engagement length
P - thread pitch
D - outer diameter of the bolt
d2 - pitch diameter
u - thread coefficient of friction
us - bolt head-surface coefficient of friction
rs - effective radius of bolt head-surface connection
T - shear strength of the weaker material - ~0.6 of tensile strength
As = 0.5*pi*L*d2 - shear area
fi = atan(u/cos(30°))
ro = atan(P/d2*pi)
F = T_hole*As - shear force
T = F*(d2/2 * tan (fi+ro)+us*rs)
Thanks





RE: Thread torque
This site might help
http://www.roymech.co.uk/Useful_Tables/Screws/Prel...
“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein
RE: Thread torque
If failure was by breaking the bolt you will be at about 75% of yield using this method. It will also give you some realistic margin of safety compared to your weakest component.