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Is the K0FF mast step safe?

K0FF described a handy little clamp on mast step on eHam.


Above are pics of the mast step.

It appears to be fabricated from 1/2″ NB galvanised water pipe with a 50mm x 6.3mm u-bolt.

Experience1 suggests the u-bolt may be undersized. Let us ‘run the numbers’.

The tensile yield strength of mild steel is about 250MPa, and its shear strength will be about 60% of that, or 150MPA. The maximum shear force on the u-bolt with a root diameter of about 5mm is 0.005^2*π/4*150E6=2.94kN. The leverage of the step with concentrated load at one end is 3.5:1, so the maximum downwards force at one end is 2.94/3.5=840N. A device like this should probably be designed with a Safety Factor of 5 (considering the chance of it slipping, or loads dropped onto it), so the Working Load Limit would be 840/5=168N or 17kg weight force.

Sure, you can probably stand on it without breaking, but such a load is at the failure limit of the u-bolt, and has no allowance for the additional forces of tools and hauling materials, dynamic loads, tolerance in bolt performance etc.

This device looks like it is an accident waiting to happen. If I saw this on a work site and did not raise it as a safety issue, I would risk prosecution under out OHS laws.

Footnotes:

1. Owen Duffy holds an Australian Licence to Perform High Risk work which includes endorsement of Advanced Rigger.


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