Bolt engineering question

[Viperwolf1]

What is the difference in the clamping force when a 5/16"-24 fastener is used in place of a 5/16"-18? Should the -24 be torqued a lesser amount to provide the same clamping force?

 

[Broncobowsher]

I have a reference manual (not with me at work today) that lists torque specs for fasteners depending on grade, size, pitch, etc. All you need to do is find the reference and look up matching fasteners with different pitch threads.

Something to confuse the situation a little. the finner thread bolt will have a thicker cross section since the threads are not cut as deep. This makes the bolt stronger and you get more clamping force to get the proper bolt stretch. But I don't know if this is more or less then the gains by shallower pitch threads?

Dang that book is at home right now.

 

[70_Steve]

What is the difference in the clamping force when a 5/16"-24 fastener is used in place of a 5/16"-18? Should the -24 be torqued a lesser amount to provide the same clamping force?

Handy table.
http://www.fandisc.com/tti.htm

 

[Broncobowsher]

The first one I look at is the 3/8" and work my way over to lubed grade 8. They are the same torque spec but the clamp load is over 10% higher.

How come none of these torque tables show a spec for "unknown rusty grade" nuts and bolts?

 

[Viperwolf1]

The first one I look at is the 3/8" and work my way over to lubed grade 8. They are the same torque spec but the clamp load is over 10% higher.

How come none of these torque tables show a spec for "unknown rusty grade" nuts and bolts?

The 10% difference is what I'm wondering about. The problem with charts is that they show max torque and the corresponding clamping force but max torque is differnet for the -18 and -24. That may be where the difference in clamping force comes from.

Rusty nuts and bolts are torque-to-snap.

 

[Larry B]

It seems funney that the grade 8 3/8 - 16 and 3/8 - 24 were the only size that torqued the same. Grade 5 bolts have 3 marks and grade 8 have 6 marks on the head but I am not aware of grade 2 and 7. How many marks do they have.

 

[mitzel]

I suggest the Billa Vista Tech section over on Pirate4x4 for a wealth of
online information on metals, bolts, etc. I'm referring to the tech writeups
rather than posting questions in the forums, this avoids the flames and
flipoffs common in the forums sections.
Tech: http://www.pirate4x4.com/tech/
Tech-Bolts/Fasteners: http://www.pirate4x4.com/tech/billavista/NutsandBolts/index.html
Also Carroll Smith has a book covering fasteners (and a number of other
topics) as part of his race car engineering books:
http://www.amazon.com/Fasteners-Plu...1_fkmr0_1?ie=UTF8&qid=1270505360&sr=1-1-fkmr0

As Broncobowsher mentioned, finer thread fasteners have a larger minor
diameter making them slightly stronger than equivalent sized coarse thread.
Given the higher strength of the fine thread the proper preload/stretch is
achieved at a higher torque and thus develops greater clamping force. I
believe the shallower fine threads do require slightly greater thread
engagement than coarse threads to avoid stripping. An off-the-shelf nut
should already be engineered such that a fully engaged bolt will yield
before the threads strip. Or for a bolt installed in a tapped hole thread
engagement for a depth of ~1.5 times the fastener diameter should
ensure sufficient thread strength.

 

[mitzel]

Larry B
> Grade 5 bolts have 3 marks and grade 8 have 6 marks on the head
> but I am not aware of grade 2 and 7. How many marks do they have.

My local hardware store (OSH) stocks grade 2,5,8 coarse and fine in
1/4"-3/4" sizes, that seems to be a fairly common selection unless you
go to more specialized vendor. Grade 2 don't have any marking.
Grade 7 have 5 lines. There may be some OEM grade 7 bolts in use on
the EB but I've never seen them commonly available at local hardware
store.

 

[Viperwolf1]

Ok. After a bunch of searching and reading I've convinced myself that the clamping force is equal per given amount of torque regardless of thread pitch. It seems that the torque applied is transferred almost directly into bolt stretch and clamping force with only minor losses for friction (which are not very different for different pitches). It just takes more arc of the torque wrench to get there with fine threads which was making me think it provided some mechanical advantage in clamping.

 

[broncnaz]

What you clamping together? Does it require the same clamping force? You only talking about a couple of Ft lbs differance in torques vs a couple hundered psi on clamping force. I cant see it being all that critical with the smaller sized bolts but then again we dont know what your clamping together. In most cases I wouldnt worry much about it.

 

[Viperwolf1]

What you clamping together? Does it require the same clamping force? You only talking about a couple of Ft lbs differance in torques vs a couple hundered psi on clamping force. I cant see it being all that critical with the smaller sized bolts but then again we dont know what your clamping together. In most cases I wouldnt worry much about it.

Intake manifold. I'm using studs instead of bolts and didn't want to over-tighten it.

 

[Dude seriously]

Fine threads are shallower, leaving more material in the middle of the bolt which results in a higher tensile strength (as mentioned by other member(s).

Coarse threads have greater sheer strength across the threads due to the change in pitch diameter.

Heat treated hardware will have a greater tensile strength.

Class 3 threads will offer greater shear strength than class 2 (commercial).

J form threads (modified root radius) offers better fatigue strength.

Everything is a compromise, picking the best combination and playing to its strength(s) is the key.

Edit - I just re-read above. Almost any good stud/nut combination is overkill for an intake manifold unless you have some super top secret rocket engine thing going on. Don’t forget anti-seize compound on any steel hardware bolting to or passing though aluminum parts.

 

[Viperwolf1]

Almost any good stud/nut combination is overkill for an intake manifold unless you have some super top secret rocket engine thing going on.

I could tell you about it, but then...well you know the rest.

 

[Pedestrian]

Curious, are studs really that much stronger? If so, why?

 

[broncnaz]

Baiscally a stud sees less torsional twisting it streches when the nut is tightened. Where a bolt twists all the way down to the threads. So the strech of a stud actually has better clamping force than a bolt. As far as how much stronger I'm not sure.

 

[broncnaz]

Originally Posted by Dude, seriously
Almost any good stud/nut combination is overkill for an intake manifold unless you have some super top secret rocket engine thing going on.

Lets see I'm pretty sure the stock 302 intake was held on with at least 4 studs from the factory and the rest were bolts I'm not real sure if the studs were fine or course threaded though. We all know the bronco didnt have no super secret rocket engine stuff going on.

Intake manifold. I'm using studs instead of bolts and didn't want to over-tighten it.

Given the torques for the fine threaded studs I dont think it will really be a issue at most I'd go with the lower spec they give for the intake torque ie 15 ft lbs if its 15-18 ftlbs. If super concerned just torque down in steps maybe 10 ft lbs the first go around then to final spec.

 

[ken75ranger]

Given the torques for the fine threaded studs I dont think it will really be a issue at most I'd go with the lower spec they give for the intake torque ie 15 ft lbs if its 15-18 ftlbs. If super concerned just torque down in steps maybe 10 ft lbs the first go around then to final spec.

That is the best way to do it. Then re-torque it once the motor is warmed up.

 

[mitzel]

broncnaz
> Baiscally a stud sees less torsional twisting it streches when the nut is
> tightened. Where a bolt twists all the way down to the threads. So the
> strech of a stud actually has better clamping force than a bolt. As far as
> how much stronger I'm not sure.

I picked up an ARP catalog at a car show last summer, besides the
part# listing it's also a great tech source. They (ARP) basically highlight
the same differences in forces as broncnaz. But I'm not sure they make
any claims regarding differences in strength or clamping force, I believe
a properly torqued bolt or stud are basically the same in those respects.
My take away was just that "studs provide more accurate and consistent
torque loading" because they eliminate/reduce the measurement
inaccuracies introduced by the twisting force/resistance interacting with
bolt torqueing.