Steering elbow

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Nov 8, 2020
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Hello all,

This is my first build but not my first rodeo. I have been concerned with the strength of my steering wheel attachments, I have opted for 20 mm downhill hubs and axels. See my pictures please. Should I be concerned with folding up the steering tubes?

Any other thoughts?

Cheers,

Leigh
 
Joined
Oct 19, 2012
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Wakefield, UK
I cant quite make out from the pictures. Are you using a hollow tube as the axle? What is the means of securing the wheel to the axle?
 
Joined
Nov 8, 2020
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5
I cant quite make out from the pictures. Are you using a hollow tube as the axle? What is the means of securing the wheel to the axle?

Yes, the black tube which is a downhill mountain bike axel is the axel. I was also concerned about its hollowness and was going to sleeve it with aluminum or steel. The quick release will go through the whole assembly and in to a threaded insert in the elbow.
 
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As a general rule a thick walled tube will perform as well as a solid in such a scenario. What's the wall thickness of the axle and is it steel or ally?
 
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When I did mine I used 2mm walled 20mm precision tube which was exceptionally strong.
I then captured the wheel hubs onto those axles with M16 12.9 hardness bolts and washers. Overkill? Certainly!
But, as I had suffered a broken shoulder from a failure in the past, I didn't want to repeat the "fun". ;)
 
Joined
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As a general rule a thick walled tube will perform as well as a solid in such a scenario. What's the wall thickness of the axle and is it steel or ally?
Thickness measures at 2.15mm at the ends and has an internal shoulder where it thickens to 3.3mm it is aluminum and no doubt a high load piece as it is designed to take big air impacts from downhill mountain biking.

My trike has a wide wheel base and is going to incorporate a small sail so the loads will be larger than average.

Leigh
 
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I doubt an aluminium tube will do. On a regular bike the axle is held at both ends. This will only be held at one. You could use an M20 bolt but it'll weigh a lot or maybe brace the existing tube with a steel insert if you can find one the right diameter and then epoxy it in.

I can't wait to see a sail on this. Looking forward to it very much. Getting it up on two wheels like a land yacht may require that M20 bolt though.
 
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I doubt an aluminium tube will do. On a regular bike the axle is held at both ends. This will only be held at one. You could use an M20 bolt but it'll weigh a lot or maybe brace the existing tube with a steel insert if you can find one the right diameter and then epoxy it in.

I can't wait to see a sail on this. Looking forward to it very much. Getting it up on two wheels like a land yacht may require that M20 bolt though.
Yes. The sheer strength in this tube is no doubt up to the task but the bending load might overwhelm it. Sleeving with steel might work but I think the plastic deformation load will be different between materials and so one might be bending while the other is breaking...I need an engineer!

I have a lathe and a little mill so making bits is not the problem.

Leigh
 
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If you make a complete new spindle a 2mm wall x 20mm mild steel tube will have the same or better bending resistance of a 17mm mild steel bolt. An M12 is generally considered the bare minimum for the job. Most bolts though are hardened well above mild steel. Given you are likely to be stressing it a lot a 3mm wall tube would be a safer bet.

You could also look to motorcycle spindles as a starting point and mill one or two of those. The problem there though is cost. Even secondhand spindles will cost. Another alternative is to get M20 bolts and drill through them with the lathe to lighten them. Not an attractive job for any tooling life I'd imagine.

I used M20 stainless bolts in one of mine and just accepted the weight. Given I was using fat tyres an extra bit of lard didn't really matter too much.
 
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Joined
Sep 16, 2018
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Netherlands
A hollow axle can work, but aluminium a c z wall thickness of 2mm isn't that much.
I used M16 and a 20mm pipe with a wall thickness of 2mm over it.
Crashed with my bike several times and m16 did not bend ad all.

I am going to switch to m12 and to be surten I got a few spare ones, but after testing them, they seems to be very strong.
 
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