Axle snapped off - Trike

the axle is 12 mm which is what is recommended from all trike literature I have read. Trouble is that where it broke is where thread is cut in and diameter goes down to 11 mm - at the highest stress point.

 

you see on Buddy's image that the Greenspeed axle has a larger diameter boss or collar at the highest stress point.
This concept is what I envisaged to improve mine , but also as suggested by AD to have a larger diameter axle next to that as well.
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I went to the Fastener shop this morning to see what they had, bad luck for me that yesterday was Public Holiday so they are having a long weekend - went to 2 others in the area as well and none were open.
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Im getting so desperate that I may have to break out the DF for a ride [ I can feel the pain just thinking about it ] as I have put on 2 Kg [ 4 1/2 LBS ] after missing just 2 days riding and that seemed to go straight on my Belly
My metabolism seems tuned to daily " marathons " .

 

yes , exactly, that is how all automotive stub axles do it. So you end up with more material at the place you need it most.
will do a search to see what bearings are available

 

I'm a Happy Chappy again.
The only delay in getting my Trike back on three wheels was the long weekend - just bad timing.
I bought the bolt this morning , 3 hrs later - all done.
So ....
Just decided to keep it simple and STRONG.!
Bought a bolt [ well was given a bolt ] a Grade 8 1/2 inch 5 inch long with the correct thread as per standard.
- Filed out the nut as spacer
- Made a spacer between bearings


here's the pieces.

 

Because I did not want weak spot where it was before , the Plain shank now goes inside the steering support - thus had to drill out threads for some of the way through the hole

 

The lovely Gold spacer made of Wonderful quality bicycle tubing came from the Raleigh of course [ thank you Raleigh for your donation ]


Fine old tubing that .
suppose the slight taper is not optimum but all the other tubes where too big.

 

This is how it bolts together - A little long thread inside but I can always cut it

 

and wheel on - because I used exactly same epacing as previously - the disk brake lines up perfectly

And tomorrow I ride into the Sunset ...... well on the way home any way.

 

Oh did I mention that ordinary bolts may have Rating of 70 000 lbs/in sqaured whereas this Grade 8 is 150 000 lbs/in squared.
So very High tensile.

 

Not that it matters all that much with respect to such large numbers, but I wonder if that axle may have failed due to shear, not tension. A common rule of thumb used to estimate shear strength is 60% of tensile strength.

 

I've seen similar recommendations, but interestingly on the Atomic Zombie bike builders forum, which I belong to, he says he has snapped 1/2" trike bolts hitting bumps and curbs, and therefore recommends 14mm at a minimum, and often 20mm for heavier riders. I always kind of figured he was just overbuilding, but maybe he wasn't, based on your picture.

 

Grade 8 or grade 5 bolts

One fabricator used grade 5 on one of my in truck bed hitches. He said
grade 8 was too brittle. Others say that is not True. Here is a simple test.

http://www.youtube.com/watch?v=FVndKEtazNg

 

Buddy and Larry , I agree there is some risk with going too brittle.
I would not be happy with a standard bolt as I would be concerned with it getting bent slightly if I hit a nastly pavement joint. With disk brakes this would be a Journey stopper.
The break does look like a shear break but the fact that it had a small portion still holding that last 3 miles [ at least that I know of ] makes me think it could not be sheared.
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Thanks A.D. I could have done an even better job if I had been at work.
I had to use an electric drill and hand hand file to flatten the spacer end off true. Would have used Lathe at work. Also would have used ordinary tubing instead of tapered tubing for the spacer.