bolt grading question

[jb1390]

Well, yes, but/and the finer pitch has a more gradual advance hence more mechanical advantage. The same torque will give a slightly higher clamp force. So the fine pitch increases the clamp directly. And then by the fact of larger root diameter it can take even more torque.
larry

The mechanical advantage hardly comes into play at all when comparing fine and coarse pitch bolts. The vast majority of the torque applied to a fastener is to overcome friction, mostly under the head of the bolt, and also along the threads. Only 10-15% of the torque of a bolt actually goes to applying preload. The change in preload between coarse and fine pitch assuming a constant torque value is negligible.

 

[jeff9366]

first I've heard of a grade 8 washer. I buy bags of bolts at menards

I use Zinc Chromate Grade 8 split/lock washers under all nuts in regular applications. I think the lower grades are worthless as lock washers.

For critical uses I use Nord Lock washers from Sweden. One Nord Lock under the bolt head, a second Nord Lock beneath the nut.

I buy Nord Lock washers via eBay.

 

[LD1]

Well, yes, but/and the finer pitch has a more gradual advance hence more mechanical advantage. The same torque will give a slightly higher clamp force. So the fine pitch increases the clamp directly. And then by the fact of larger root diameter it can take even more torque.
larry

:thumbsup:

 

[SPYDERLK]

Well, yes, but/and the finer pitch has a more gradual advance hence more mechanical advantage. The same torque will give a slightly higher clamp force. So the fine pitch increases the clamp directly. And then by the fact of larger root diameter it can take even more torque.
larry

The mechanical advantage hardly comes into play at all when comparing fine and coarse pitch bolts. The vast majority of the torque applied to a fastener is to overcome friction, mostly under the head of the bolt, and also along the threads. Only 10-15% of the torque of a bolt actually goes to applying preload. The change in preload between coarse and fine pitch assuming a constant torque value is negligible.

I have hi lited the pertinent word as far as degree of clamp force increased directly. ... Perhaps you missed it.

 

[SPYDERLK]

I use Zinc Chromate Grade 8 split/lock washers under all nuts in regular applications. I think the lower grades are worthless as lock washers.

For critical uses I use Nord Lock washers from Sweden. One Nord Lock under the bolt head, a second Nord Lock beneath the nut.

I buy Nord Lock washers via eBay.

The problem with lock washers is that they can camouflage a problem. They can prevent a bolt in an inadequately clamped joint from turning and getting obviously loose. The joint moves and wears itself out. A correctly tightened joint will not loosen or wear because it doesnt move.

 

[DarkBlack]

There's a nice chart here on bolt strength capabilities by size and grade-both in tension and shear.

Grade 5 vs Grade 8 Fasteners - TineLok

One aspect to be careful about is when you side load a tightened fastener (think shear), you are also pulling against the friction that the clamping of the bolt provides. A pure friction joint will use enough bolts that the clamping load will be enough to cause none of the bolts to be loaded in shear. For this reason, don't ever tighten your shear bolts!!! Use a lock nut and run them loose.

I don't buy it.
I run mine tight, both because of mechanical theory and real experience. As far as tractor stuff goes, you'll find implement designers who agree with me. In fact I'm looking at a manual of an implement I own, right now, that states to make sure the shear bolt is kept very tight.

 

[DarkBlack]

Well, yes, but/and the finer pitch has a more gradual advance hence more mechanical advantage. The same torque will give a slightly higher clamp force. So the fine pitch increases the clamp directly. And then by the fact of larger root diameter it can take even more torque.
larry

Correct.

 

[LD1]

As far as a shear bolt goes in a rotating hub, you are not tightening it enough to create any friction between the shaft and hub

 

[SPYDERLK]

As far as a shear bolt goes in a rotating hub, you are not tightening it enough to create any friction between the shaft and hub

Yeah. - Flange shear like on a baler is where friction would come in. I tighten~40% of bolt spec to prevent jiggling impact.

 

[newbury]

I use Zinc Chromate Grade 8 split/lock washers under all nuts in regular applications. I think the lower grades are worthless as lock washers.
<snip>

Split lock washers are essentially a flat washer.

The lockwasher serves as a spring while the bolt is being
tightened. However, the washer is normally flat by the time
the bolt is fully torqued. At this time it is equivalent to a solid
flat washer, and its locking ability is nonexistent. In summary,
a lockwasher of this type is useless for locking.

From NASA Reference Publication 1228, Fastener Design Manual. Those are the people who want to make sure things don't loosen up. It's a long way from the moon to Florida to get another nut.

When I assembled my trailer enclosure conversion the first time I researched a bit the best way to ensure I didn't leave my nuts all over the road. About the easiest way was a drop of loctite, some extra thread and retightening. I've got about 160 nuts on my conversion, and I didn't like the expense of 160 locknuts.
So far in about 4,000 miles I've "lost" two regular nuts.


There is always the tradeoff between having a bolt/nut combo that won't come loose under normal operation, is inexpensive, yet easy to loosen when you want to.