Truvativ crankset. Made of cheese?

[Yellow Saddle]

In my experience of working on cars and bikes in general, 2 or 3 times I have stripped threads due to the bolt or female thread having a manufacturing defect. Ie the material can be too soft or the thread spiral can be angled differently on the nut than it is on the bolt. Whilst I agree truvative is a reasonable brand, it is probably not cost effective for them to undertake quality control checks on 100% of the components they import that make the final product.

Cranks are forged from vats of molten aluminium. What do you think the chances are that one crank's worth of different aluminium is slipped into the production line?

Cranks are threaded by a machine that does thousands of threads a day, using a single tool fitted into a single lathe. What do you think the changes are that during lunchtime, someone slips a different tool onto the machine that has a slightly different thread than the standard?

I think the chances of user/installer error are larger.

 

[Yellow Saddle]

WARNING - Just don't do the above in public, you might get arrested, or at least some very strange looks.

When I was a little kid in primary school, we had, once a week, a lesson in using the library. Whenever the teacher used the word "title" and write it on the board, a few boys (not me of course) would giggle and snigger. The trigger was the first part of title that spells...tit. Mrs Momberg one day stripped her thread, turned red and asked us, I mean, them, what was so funny. She knew, the boys knew, but no-one would say.

Ever since them I tried not to read double entendres into everything except when I'm drunk, which of course never happens.

But I do have my fun with it nevertheless. Whenever I used to teach engineering students the concept of mechanical precession, I would use the gesture suggested above and encourage them all to do the same. All with a straight face. I am 100% sure than wherever they find themselves today facing a precession puzzle, out comes the finger and O and voila, problem is solved.

The trick in class is to never pump, just turn. I hope this last tip helps.

 

[sleuthey]

Cranks are forged from vats of molten aluminium. What do you think the chances are that one crank's worth of different aluminium is slipped into the production line?

Incredible. More likely to be impurities. The OP was correct to ask others in case there had been a faulty batch.

Cranks are threaded by a machine that does thousands of threads a day, using a single tool fitted into a single lathe. What do you think the changes are that during lunchtime, someone slips a different tool onto the machine that has a slightly different thread than the standard?

Incredible. More likely to be a jig alignment issue or an apprentice operating the lathe on a Friday afternoon.

I think the chances of user/installer error are larger.

I completely agree. This had been mentioned already so I would have got board repeating it when there are other possibilities.

 

[Yellow Saddle]

Incredible. More likely to be impurities. The OP was correct to ask others in case there had been a faulty batch.


Incredible. More likely to be a jig alignment issue or an apprentice operating the lathe on a Friday afternoon.


I completely agree. This had been mentioned already so I would have got board repeating it when there are other possibilities.

Getting board is incredible.

 

[Gravity Aided]

Unless you are a carpenter.

 

[raleighnut]

Cranks are forged from vats of molten aluminium. What do you think the chances are that one crank's worth of different aluminium is slipped into the production line?

Cranks are threaded by a machine that does thousands of threads a day, using a single tool fitted into a single lathe. What do you think the changes are that during lunchtime, someone slips a different tool onto the machine that has a slightly different thread than the standard?

I think the chances of user/installer error are larger.

Hate to pick you upon something but you can't 'Forge' molten metal, you can cast it though.
Forging is when you take a solid piece of metal, heat it til it's malleable then stamp it to shape in a die.
Casting can either be in a sand 'mould' or a metal 'Die' mould hence the terms 'Diecast' and 'Sandcast'

 

[winjim]

In case anyone's interested, here's what happened.

Here's the pedal as it pulled out.

Close up showing the threads.

View of the inside of the crankarm. Nice clean intact threads here.

View of the crank once I'd got it home and removed the pedal. Only half the threads have stripped.

So it does seem that for whatever reason the pedal wasn't fully tightened, then as I've gone over the speed bump the increased load has pulled it out.

Like I say, it was fixed straight away so this is all academic really.

 

[Yellow Saddle]

Cranks are forged from vats of molten aluminium. What do you think the chances are that one crank's worth of different aluminium is slipped into the production line?

Cranks are threaded by a machine that does thousands of threads a day, using a single tool fitted into a single lathe. What do you think the changes are that during lunchtime, someone slips a different tool onto the machine that has a slightly different thread than the standard?

I think the chances of user/installer error are larger.

Hate to pick you upon something but you can't 'Forge' molten metal, you can cast it though.
Forging is when you take a solid piece of metal, heat it til it's malleable then stamp it to shape in a die.
Casting can either be in a sand 'mould' or a metal 'Die' mould hence the terms 'Diecast' and 'Sandcast'

Of course, but I wuz taking shortcuts. There is a nice Utoob of how cranks are forged. Molten alu is cast into an oversize die and that casting is then forged. Even after the forging there are bits which have to be machined off, just like on a casting. This admission of course exposes me to another possible stage where someone could slip a fake forged crank with incredible imperfections into the production line.

User error is seldom admitted, blame is always upstream with the disciplined production process.

 

[Drago]

Holy Mary Mother of Boris! I reckon that's been badly fitted rather than a fault with the crank arms themselves.

 

[raleighnut]

Of course, but I wuz taking shortcuts. There is a nice Utoob of how cranks are forged. Molten alu is cast into an oversize die and that casting is then forged. Even after the forging there are bits which have to be machined off, just like on a casting. This admission of course exposes me to another possible stage where someone could slip a fake forged crank with incredible imperfections into the production line.

User error is seldom admitted, blame is always upstream with the disciplined production process.

Ah the 'forging' would change the molecular structure of the Aluminium, a bit like 'cold drawing' a tube it reduces the 'grain' size within the metal.