/ Grivel 360 screw thread upside down?

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CurlyStevo - on 31 Oct 2012
On ice screws the ridge the thread consists of is not symmetrical, one side of the ridge is sloping and the other side is vertical.

Now to my mind BD have it the right way around. The vertical side is such that if you try and pull the scew out of the ice the vertical side is pushed against the ice. Grivel screws it's the other way around. Anyone know why?

http://www.google.co.uk/imgres?q=grivel+360&um=1&hl=en&sa=X&biw=1486&bih=770&...

http://www.google.co.uk/imgres?q=black+diamond+express&um=1&hl=en&biw=1486&bih=770&a...
Stevo
Marek - on 31 Oct 2012
In reply to CurlyStevo:
Probably makes little difference, but the Grivel-way might have advantages in terms of load spreading on the ice in the hole. It will also tend to compress (strengthen) the ice threads in the hole rather than sheer/rip them. Total guesswork I admit.
matejn - on 31 Oct 2012
CurlyStevo - on 01 Nov 2012
In reply to Marek:
I maybe assumed that having a sloped profile would make it more likely to slip, but I kind of see what you mean.....
In reply to CurlyStevo: other firms have done this down the years as I remember. I suspect it doesn't make a huge difference, but Grivel threads have been that way around for what seems like forever.

I'll go and check my old screws and see which make does which later! :)
edinburgh_man on 01 Nov 2012
In reply to CurlyStevo:

Steve,

Stevo,

I was speaking to the Grivel distributor the other day about exactly this.

Grivel threads are designed this way so that when loaded the force is spread though the ice at a roughly 45 degree angle from the screw.

This design spreads the force over a greater area of ice - and importantly helps to prevent the ice directly around the screw failing.

IMO - a much better design than the BD thread.


Marek: well done - pretty much bang on!
seaofdreams - on 01 Nov 2012
In reply to rosmat:

thats correct, this the same as with a dead man or stake, where the "point" is always forward (towards the pull) thus spreading the load into the snow or turf or mud or heather (or faith).

iksander on 02 Nov 2012
In reply to Marek: I read something recently that backs this up - no appreciable difference in pull strength between "normal" and inverted threads. Haven't been able to find it again though...

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