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General Climbing Discussion

Topic Date User

easy method to groove stainless rings / Ubolts 18-Sep-2008 At 3:11:32 PM atreyudelacy

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I think if anybody is to use this method of cutting their own thread/notches, then very close attention should be paid to the depth of the notching. I prefer hotgemini's idea of using a rig that will result in a more standardised process, ideally this should also include some sort of depth indicator. The shear and tensile capacity of the bolt is determined by the grade of the material and the cross-sectional area of the bolt. Obviously any reduction in the bolt diameter will result in an exponentially reduced cross-section. Also, as mike has pointed out, the notches should not be too close to the surface of the rock, this is important in both tensile and shear loading scenario's. If you take the more common shear loading for example, and look at the failure mechanism as noted by Steve Hawkshaw in his thesis, you will see that the as the surface of the rock undergoes local crushing, a bending moment occurs in the bolt. Where the tensile and shear capacity is governed by area (r ^ 2), the bending capacity is governed by what's called the 'moment of inertia' (r ^ 4, i.e A 10mm bolt with 1.25mm deep thread - i've taken this to mean that the min diameter will equal 7.5mm - will only have 32% of the bending capacity that a plain 10mm bolt would), this leads back to the significance of reducing the diameter of the bolt. Given that the R8 (316 SS) anchor in steve's tests did not even meet the min requirements, i would suggest that it would be very dangerous to have a minimum diameter (taken at the thread, not at the shank) less than 8mm, ideally not less than 10mm.