Thread: Crappy bolts...Part II (With Photos!)

you can see the thread imprint on the
"recovery point" bolt hole

bolts too short,,
and recovery point metal too soft.

I think theres a lesson in here for all of us,,,

Originally Posted by Disco_owner

sam

another words , what you are trying to tell us is that you didnot have a recovery point , and I don't man attaching the snatch strap to the Aluminium pipes or where they bolted onto the chasis , and if the Driver Trainer went over your car which they must do i they are certified , he didnot pick up on the fact that you didnot have a proper recovery point and should not have let you continue with the driver training in the 1st place as he has jeopardised your safety and the safety of other in this exercise.

There was a recovery point (as mentioned before he was at least the third person to check it out and give it a clean bill). The recovery point was bolted to the chassis. The bar was in turn attached to the recovery point. It is the piece of metal between the tubing and the thin black piece of metal

If the bar had got ripped off because the strap had been attached directly to the bar then that would have been stupid and the end result expected.

But, the type of bar is not at fault, nor, as I see it, is the recovery point. It was the crucial connection to the chassis (ie the bolts) that failed. Once they failed the recovery point continued onwards with the bar firmly attached until the stress put on to the other end caused it to shear off.

I went on a trip with Sam a few weeks ago and the first thing i checked when i met up with him was that recovery point. I can say that the recovery point looked substantial enough to me, quite comparable to my 4x4 intelligence points. What i did not look at was the bolts, i assumed wrongly that the bolts where high tensile. So i don't think their was anything obviously wrong with the recovery point, i was happy for Sam to join me.
If i had not felt it could take the punishment of a snatch we wouldn't have gone to abercrombie nat park.

Aaron

ditto what Pedro said.
A bolt in shear is only as strong as it's minor diameter, in this case the root of the thread, which is a much smaller diameter than the shank and therefore much weaker.
With any bolt in shear, the bolt should have been chosen for the correct grip length (unthreaded shank) to pass through both plates and the excess thread then trimmed.

AN series airframe bolts come in 1/16" length increment grip lengths for this reason.

BTW, any chance of a photo of the bolt head stamp ?

Originally Posted by rick130

ditto what Pedro said.
A bolt in shear is only as strong as it's minor diameter, in this case the root of the thread, which is a much smaller diameter than the shank and therefore much weaker.
With any bolt in shear, the bolt should have been chosen for the correct grip length (unthreaded shank) to pass through both plates and the excess thread then trimmed.

AN series airframe bolts come in 1/16" length increment grip lengths for this reason.

BTW, any chance of a photo of the bolt head stamp ?

If I can find the bolts (they were just chucked in the back of my car with the bar after the incident) I'll take some pics. I'll also take some more pics to show the setup and connection of the recover point and bar a bit clearer to reduce the confusion it is causing. Pics won;t be here until Friday at the earliest though cos I am in Melb all this week and my car is in Sydney.

Originally Posted by rick130

ditto what Pedro said.
A bolt in shear is only as strong as it's minor diameter, in this case the root of the thread, which is a much smaller diameter than the shank and therefore much weaker.
With any bolt in shear, the bolt should have been chosen for the correct grip length (unthreaded shank) to pass through both plates and the excess thread then trimmed.

AN series airframe bolts come in 1/16" length increment grip lengths for this reason.

BTW, any chance of a photo of the bolt head stamp ?

A bolt in tensile strain is only as strong as the minor diameter - a bolted joint correctly designed in double shear, should be as strong as the major diameter, as the shear forces should be acting on the shank and not the thread (i agree - not always possible with standard sizes).

Personally I don't consider that as a proper recovery point - it is just an L cut from flat bar - there is no hole to secure the shackle - and stop it sliding away from the bolts - putting more leverage on the joint. However - I am pretty sure the failure occurred because the bolts were not appropriate. I would also be interested in the bolt head pics if you can manage them.

Originally Posted by isuzurover

there is no hole to secure the shackle - and stop it sliding away from the bolts - putting more leverage on the joint.

I'm not quite sure what you mean. I assume the shackle pin goes through a hole (not visible, hidden by tubing) lower down in the plate.

In the pic above, what is the thinner bracket at the rear that appears to have been welded to something alont the top edge? Perhaps it's just the edge having been cleaned that makes it look like a broken weld.

Ron

Originally Posted by isuzurover

A bolt in tensile strain is only as strong as the minor diameter - a bolted joint correctly designed in double shear, should be as strong as the major diameter, as the shear forces should be acting on the shank and not the thread (i agree - not always possible with standard sizes).

Twice as strong (assuming threads are excluded from the shear plane).
Double shear connections are generally too difficult/costly to achieve in vehicle construction. Any plate bolted to a chassis rail is a single shear connection. The only way to achieve double shear would be to have 2 plates from the bar, one on either side of the chassis rail, with a bolt through the lot.