axial force generated by 3/8-16 bolt with a given torque
axial force generated by 3/8-16 bolt with a given torque
(OP)
I have seen the simplified formulas of bolt clamping which is similar to what I am trying to figure, but wanted to know if this is correct. If want to find out how much force is generated on the end of the .375-16 bolt being screwed into a tapped hole when metal hits metal (the end of the .375 screw, not the head), or if I can compress a spring etc... I understand that friction may be a large variable. Either the steel bolt bottoming out on a sleet flat, or if compressing a spring... if I am applying a known torque of 120in-lb.
Do I not need to find the mechanical advantage first of the thread first? (thd dia*pi/pitch) .375*pi/.062= 19 MA
Then divide 120in-lb by thread radius.. 120in-lb/.1875in=640lb then multiply by the mech advantage 640lb*19=12,160lb ? this sounds high. Is this wrong? I understand that friction has not yet been accounted for. Before friction and assuming the head of bolt of screw does not bottom out is what I am curious of. Or, how far off is the above calculation. Please explain if I have missed the boat. If I am close, please comment on how the friction coefficient would then be applied. I have done this before years ago and had our ME check and I believe I was correct. I have forgot much since then. thanks
Dia=.375"
Torque=120 in-lbs
pitch=.062"
Do I not need to find the mechanical advantage first of the thread first? (thd dia*pi/pitch) .375*pi/.062= 19 MA
Then divide 120in-lb by thread radius.. 120in-lb/.1875in=640lb then multiply by the mech advantage 640lb*19=12,160lb ? this sounds high. Is this wrong? I understand that friction has not yet been accounted for. Before friction and assuming the head of bolt of screw does not bottom out is what I am curious of. Or, how far off is the above calculation. Please explain if I have missed the boat. If I am close, please comment on how the friction coefficient would then be applied. I have done this before years ago and had our ME check and I believe I was correct. I have forgot much since then. thanks
Dia=.375"
Torque=120 in-lbs
pitch=.062"





RE: axial force generated by 3/8-16 bolt with a given torque
I am a little confused about what your question is but I think what you are asking is :- if you tighten a bolt or screw until the shank hits metal but the head is in fresh air what will the force be exerted on the bottom of the bolt shank as it is torqued to 120 lb -in.
That being the case to me you would exert a force approximately given by the formula F= T/(0.2*d)
So F = 120/(.2*0.375) = 1600lbf
RE: axial force generated by 3/8-16 bolt with a given torque
Or is your 1600 lbf valid as a force (coming from the total of the threads being tightened to failure around the helix of the whole 3/8 dia bolt, but that 1600 lbf being distributed only across the area touching at the bottom of the drilled hole?
(A drilled and tapped hole being assumed to tapped all the way down, and the drilled hole being the usual 118 degree conic end? )
RE: axial force generated by 3/8-16 bolt with a given torque
RE: axial force generated by 3/8-16 bolt with a given torque
http://www.spaenaur.com/pdf/sectionD/D48.pdf
https://www.kimballmidwest.com/catalog/MarketingTe...
page 32 here -
http://www.holo-krome.com/pdf/Consolidated_Tech_Ma...
RE: axial force generated by 3/8-16 bolt with a given torque
RE: axial force generated by 3/8-16 bolt with a given torque
If the threads are being used to raise and lower a load then the equations on this site might be useful.
http://www.roymechx.co.uk/Useful_Tables/Cams_Sprin...
RE: axial force generated by 3/8-16 bolt with a given torque
at first i thought the question "nuts" but then i thought "aren't you "just" stretching the bolt against the bottom of the hole?"
next thought was "how do you torque engine block studs?" i can't imagine that these bolts are bottomed out; is there just so much friction in the block threads?
Quando Omni Flunkus Moritati
RE: axial force generated by 3/8-16 bolt with a given torque
Except his coefficient value of 0.2 might be as low as 0.1 or as high as 0.4 depending on material, lubrication, plating, surface finish etc.
"How do you torque engine block studs?" You don't you torque a nut on the end of the stud.
RE: axial force generated by 3/8-16 bolt with a given torque
Quando Omni Flunkus Moritati
RE: axial force generated by 3/8-16 bolt with a given torque
That is assuming a lot about things like plating, hardness, surface finish etc.
The simple way is to just rig up a little test fixture with a transducer mounted at the end of the tapped hole and run a few tests.
RE: axial force generated by 3/8-16 bolt with a given torque
the tapped hole is essentially the nut of a conventional fastener. preload is developed between the head of the bolt and the tapped hole because the end of the bolt isn't restrained and the bolt can stretch.
if you torque a bottomed out screw, very quickly you'll strip the thread.
no?
Quando Omni Flunkus Moritati
RE: axial force generated by 3/8-16 bolt with a given torque
RE: axial force generated by 3/8-16 bolt with a given torque
preload is the force created as the bolt stretches.
in your case, i think you're "just" compressing a spring, F = kx.
Quando Omni Flunkus Moritati
RE: axial force generated by 3/8-16 bolt with a given torque
Johnny Pellin
RE: axial force generated by 3/8-16 bolt with a given torque
Solve the equation for Q with your givens.
Ted
RE: axial force generated by 3/8-16 bolt with a given torque
RE: axial force generated by 3/8-16 bolt with a given torque
Ted
RE: axial force generated by 3/8-16 bolt with a given torque
If you need the exact force you will need to test and measure. All the other methods listed will just give you a theoretical value.
I used the same torque and screw diameter as first described and after 10 tests the average was a resultant force of 1375 lbs not the 1600lbs. Actual values ranged from 1335 to 1398lbs.
RE: axial force generated by 3/8-16 bolt with a given torque
RE: axial force generated by 3/8-16 bolt with a given torque
As for the resulting max net axial force at the bolt tip that would be produced by torquing the 3/8-16 bolt to 120 in-lbs, you would need to reduce the mechanical advantage of the threads by the friction losses in the thread contacts and the tip contact. At higher torques applied to the bolt head, you would also need to allow for some torsional deflection in the bolt body. And lastly, there is usually a large difference between static (breakaway) and sliding friction coefficients. This difference can be up to 100%. Personally, I would also use a bare-metal-on-bare-metal friction coefficient of 0.30.
RE: axial force generated by 3/8-16 bolt with a given torque
Superbolt