Breaking point

[Shoogle]

Today I noticed my saddle was a bit squint so I undid the clamp bolt, straightened up the saddle and, when re-tightening the bolt, it snapped. I know I should use a torque wrench but it's a tool I don't have yet. I've done it with a hex key skewer as well. What could have happened if I'd tightened the bolt or the skewer to just a fraction under breaking point? Would it still be at risk of breaking?

[NATURAL ANKLING]

Hi,
Plenty posts here on single bolt designs, the trick is either a two bolt design or change the bolt often, cant find other post at the moment, someone else will chirp in.

P.S. the drill hole in the centre of the bolt is suspicious........................?

[Brucey]

it might help if you show what the rest of the assy looks like.

There is no way to be sure what happened exactly but it might be a good idea if you got a torque wrench.

cheers

[NATURAL ANKLING]

Hi,
It is steel is it?
Not sure about the colour.

[Shoogle]

It’s the ‘Hope' clamp with the teardrop nut. The main reason I don't have a torque wrench is that I've managed 36 years of cycling without one but it'll be my next purchase.

[NATURAL ANKLING]

Hi,
Ok I thought is was the actual saddle - pillar rail clamp, as you were talking tilt drop etc in opening post IIRC.

Anyway the hole up the centre to lighten (that hole is not required for manufacture at all!) is a dangerous silly habit of fashion over safety.

What is the material?
Steel
Titanium
Aluminium

[Valbrona]

Your title 'Breaking point' doesn't say much about what this thread is about.

[Vorpal]

It's here

[Brucey]

It’s the ‘Hope' clamp with the teardrop nut. The main reason I don't have a torque wrench is that I've managed 36 years of cycling without one but it'll be my next purchase.

Failing memory here but does that mean the bolt is aluminium? IIRC it is something like M7 thread (that easy-to-find size... ).

IMHO aluminium bolts are a daft idea (they lack many of the useful properties of steel ones) and almost without exception seat binders which have a rotating bolt are basically a dumb idea; it is far better to have a rotating nut (or sleeve) instead. The threaded part sees a bending load in any event and with the latter arrangement allows the male threaded part to bend once and once only instead of fatiguing every time the clamp is moved.

Even the classic campag seat binder bolt is designed exactly wrongly... if the pip were on the other half of the bolt it would work perfectly, as it is they (and their many clones) break with monotonous regularity.

Possibly you don't need a torque wrench after all, just a better design of seat binder...

cheers

[NATURAL ANKLING]

Hi,
My mate went for Hope Wheels, probably 11.5 grams lighter than the competition............

[Vorpal]

It looks like steel to me. Furthermore, it's looks like it cracked slightly and rusted before the recent failure, or perhaps it had a defect.

It's also possible that the rust increased the torque required enough to cause the failure. Or that the defect combined with the increased torque to create the failure.

In any case, given the little bit of rust where it shouldn't be, I think it would have failed before long, even if you had torqued it correctly.

[Brucey]

IIRC that bolt is usually aluminium in the hope clamp



the 'rust' could be some of the grot that is evident elsewhere in the thread valleys...?

cheers

[Shoogle]

The original point of the thread was about tightening the bolt, skewer etc, to just below breaking point. Is it safe?

[Brucey]

not if

a) the part has little or no ductility (most parts deform before they break)
or
b) there are other service loads that are superimposed on the preload.

In the latter case you can have high preload or high service stresses, but not both.

There are some parts that are sensitive to environment too; for example if you spray highly stressed parts with road salt, they can suffer stress corrosion cracking (SCC).

cheers