Are higher grade bolts more brittle?

I've cut, drilled & tapped grade 8s plenty of times, honestly I haven't really noticed a differerence from anything else.

H.

It's a requirement that you can hammer the bolt's head onto a surface tilted

15 (IIRC) degrees (bolt sticking in a hole) without fracture. They really aren't brittle. Just more brittle than the soft iron grades with 6 or even worse 4.

Nick

I haven't heard of that requirement, but it sounds sensible. Nevertheless, I've seen wedge-shaped washers (5 degrees I think) which are placed under bolts passing through the flanges of universal beams in structural steelwork. Presumably to make a neater job of the work, and perhaps because the bolts are too big to hammer.

Best wishes,

Chris

I drilled some and also did not see much difference. I would suppose that using bolt cutters would be more difficult.

i

Yes + LOL!

Nick

A good article that EXPLAINS things well.

On Tue, 15 Jan 2008 07:48:04 -0800, with neither quill nor qualm, Gunner quickly quoth:

Fuzzy, round not-dice? Got it.

--- Chaos, panic, and disorder--my work here is done.

No markings on the head are typically grade 2, crapy bolts, not good for much!

As long as the bolts are properly torqued and everything fits snuggly it will be no problem as they will be almost totally in tension. If loose or ill-fitting parts, the bolt can be in shear, and they are more likely to fail than a grade 5 or 8.8

Most trailer hitch attachment bolts are grade 5 (and a lot are either grade 2 or ungraded

"Ignoramus25819" wrote:..

Thanks, Iggy, I'll keep that in mind the next time I put in an order.

Jon

They are about 20 miles away from me and I always get their stuff the next day. I am usually pleasantly surprised by their stuff

i

You guys may find this interesting.

A number of years ago a friend of mine was the Service Manager for a large Caterpillar dealer. They began having fracture problems with grade 8 bolts (or maybe grade 8 studs) on the diesel engine oil pans. They replaced numerous oil pan bolts and they still kept breaking.

Ken (my buddy) while not being trained as an engineer was a pretty sharp guy. He noted that the shop had begun to use automotive silicon in place of the composite oil pan gasket. He thought that the silicon was allowing the oil pan to "float" slightly causing a high frequency vibration that was inducing stress fractures in the grade 8 bolts. He ordered the shop to resume using the original gaskets and the problem never recurred!

His theory made sense to me. What do you think?

Lucky you! For me, they're well worth the expense, but shipping tends to cost as much as the product -- or more...

On Wed, 16 Jan 2008 04:36:18 GMT, with neither quill nor qualm, "toolman946 via CraftKB.com" quickly quoth:

I think his other instruction (to torque the bolts instead of just using the 1/2" impact driver until stalled) was the key. But that's just me.

--- Chaos, panic, and disorder--my work here is done.

Indeed, the shear force is intended to be carried by friction, not the bolt itself. But I'm not sure that high tensile bolts would be more likely to fail in shear. Perhaps someone else knows for sure?

Best wishes,

Chris

It seems possible that the bolts were cracking as a result of fatigue cracks growing slowly due to the vibration. But I suspect this could only happen with a very rubbery gasket material.

Best wishes,

Chris

That's possible, if he actually said that!

Chris

No, they aren't more likely to fail. If the softer one is bent, he already failed.

Nick

Here we go again; Bolt vs Screw I interpert as follows: Bolt requires a nut Screw goes into a threaded hole on something

Unless youre talking to a woodworker. :-) ...lew...