Thread forming screw head
Thread forming screw head
(OP)
I have a #4 thread forming screw with T8 drive head and another with T7 head drive. If I'm applying the same torque on both screws with all other parameters to be same (the only the difference is T7 and T8), would I get less clamping force on the joint with the screw that has T8 drive?
Thanks
Kinsrow
Thanks
Kinsrow





RE: Thread forming screw head
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Thread forming screw head
Please correct me.
Thanks
RE: Thread forming screw head
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Thread forming screw head
CoryPad is right on the money with his answer which could be translated as:
"Torque is torque (as long as you're along the same axis"
APDESIGN
RE: Thread forming screw head
radius. It does not matter whether it is
a slot, phillips, hex, or whatever drive.
The force times the radius is the same.
The stress on the different T drive heads
does increase as the T drive gets smaller.
This would be analogous of useing a 1/4 or
1/2 drive head. You can get the same torque
for either, but you might break the drive
head. The torque is created by the force
on the handle of the driver irregardless
of the sixe of the drive head.
RE: Thread forming screw head
Thanks!
Kinsrow
RE: Thread forming screw head
I feel that an attempt to consolidate drive sizes is going to be the offshoot of this question and I need to tell you that it is not quite as easy as it seems. If you go to the smaller drive you will be applying a greater proportion of it's endurance limit at the seating torque and as a result your tool life may suffer. Putting the larger drive may cause heading problems and head strength issues. Drive size changes need to be looked at carefully; we spent several manyears creating head standards for our last drive system development project.
RE: Thread forming screw head
Kinsrow
RE: Thread forming screw head
RE: Thread forming screw head
RE: Thread forming screw head
Friction under the head is a factor in determining how much of the input torque goes toward achieving preload.
However a larger head may not necessarily lead to higher friction forces, no matter what they taught us in school abou F = mu x N.
Contact stresses, deflection and surface finish also all come into play.
So, as is always the case with threaded fasteners, if you really need to know how much preload you are achieving, you have to test your specific application.
RE: Thread forming screw head
With a thread forming screw the head friction to all of the other things that "absorb" torque without producing useful preload is much smaller than for regular threaded fasteners.
So in the particular case under discussion, the difference in head size is probably trivial, and probably less than the scatter from joint to joint.
RE: Thread forming screw head
I fail to see how we missed a point when:
If the bearing surface is allowed to be different, then all things are not the same. We weren't allowed to consider that option, hence the original answers of "it doesn't matter", with the caveats of no drive system plasticity or crack initiation/propagation.
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.