How does this happen?

8 years ago
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musorianin
musorianin
QLD
597 posts
QLD, 597 posts
8 Apr 2018 10:33am

I've broken a few booms over the years but not here on the tail piece like this. Only a couple of seasons old and no major impacts I can remember. Just metal fatigue? But is that section under much load?
decrepit
decrepit
WA
12884 posts
WA, 12884 posts
8 Apr 2018 12:49pm
I've never seen that before, but just thinking about it, that crack will close as you close the arms and open up as you open them. So the arms are forced more open as the boom flex's with riders weight and when it's at minimum extension. So just a guess here, but looks like you've put load on it at close to minimum extension.
Does that make sense?
Mark _australia
Mark _australia
WA
23682 posts
WA, 23682 posts
8 Apr 2018 12:59pm
I'm calling maybe metal fault from the start - mandrel bending stretches the tube a helluva lot so any fault in metal would be a weakness, later tempering could have been a bit off, who knows.
A clever metallurgist type would pick that easy from the grain structure
Imax1
Imax1
QLD
4950 posts
QLD, 4950 posts
8 Apr 2018 4:27pm
Id say its where the tube is seam welded. Probably the worst place to be on a mandrel bent curve. It would try to sheer between the stretched outside and compressed inside curve. Possibly already unseen cracked before use. Culprit ,cheap tube.
Tardy
Tardy
5354 posts
5354 posts
8 Apr 2018 4:31pm
i think its a good time to get a carbon boom .

done a few alloys ,it usually breaks at the adjuster ?? weird one ...had a carbon boom for 9 years now .great investment .
Mark _australia
Mark _australia
WA
23682 posts
WA, 23682 posts
8 Apr 2018 7:03pm
Imax1 said..
Id say its where the tube is seam welded. Probably the worst place to be on a mandrel bent curve. It would try to sheer between the stretched outside and compressed inside curve. Possibly already unseen cracked before use. Culprit ,cheap tube.


Good point, they don't use SHT for booms huh
Max Phunn
Max Phunn
19 posts
19 posts
8 Apr 2018 8:07pm
Any chance water was left in there and it froze at some time?
NotWal
NotWal
QLD
7436 posts
QLD, 7436 posts
9 Apr 2018 8:45am
It's green. That's what happens when you make your booms out of garden cuttings. You need proper teak.
musorianin
musorianin
QLD
597 posts
QLD, 597 posts
9 Apr 2018 11:21pm
So maybe a fault, or s***y tube. Thanks for the thoughts. Like to go carbon but...$$$ ... maybe tho
At least I found a decent tail piece in my boom graveyard to replace it. I'm also wondering how long I've been chugging around with that crack, or how much longer it would have held on...
Mark _australia
Mark _australia
WA
23682 posts
WA, 23682 posts
10 Apr 2018 2:46am
Max Phunn said..
Any chance water was left in there and it froze at some time?


Not so much in Queensland
Tardy
Tardy
5354 posts
Max Phunn
Max Phunn
19 posts
19 posts
10 Apr 2018 5:03am
Mark _australia said..

Max Phunn said..
Any chance water was left in there and it froze at some time?



Not so much in Queensland


Sorry, I am from Canada eh.
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