Hex head flange screws…
Discussion
I hope the title has piqued your interest.
Do you know the shear force/breaking point of 6mm hex head screws.
For context they will be securing a roof anchor with a 120kg man attached to it. They to withstand him/me falling from height.
The roof anchor is 4 mm steel,the 7 fixing holes 6.5mm.
The screws 6mm x 50mm screwed into timber.
Steel or stainless?
Do you know the shear force/breaking point of 6mm hex head screws.
For context they will be securing a roof anchor with a 120kg man attached to it. They to withstand him/me falling from height.
The roof anchor is 4 mm steel,the 7 fixing holes 6.5mm.
The screws 6mm x 50mm screwed into timber.
Steel or stainless?
Way to many variables here -
- which brand and length of screw
- what you are fastening into
- what is the anchor
- how far are you falling - a slip and load is fraction of a 3m free fall
- what ropes and harness, and are they impact absorbing
(etc)
As a climber, I have in the past used big slings around chimney pots and once a rope led into a roof window with belayer...plus great care.
- which brand and length of screw
- what you are fastening into
- what is the anchor
- how far are you falling - a slip and load is fraction of a 3m free fall
- what ropes and harness, and are they impact absorbing
(etc)
As a climber, I have in the past used big slings around chimney pots and once a rope led into a roof window with belayer...plus great care.
The shear force of the screws depends on what they’re made from. Just as important is what they are screwed into.
Personally, I wouldn't be trusting my life to any number of 6mm screws into wood, especially if they are only going 50mm into the wood.
Have a look at the anchor bolts that window cleaners / maintenance engineers use when they’re on the outside of a building. Quite similar to car harness eye bolts.
In fact - look at the size of a seatbelt bolt - that should give you an idea of the strength you need.
Personally, I wouldn't be trusting my life to any number of 6mm screws into wood, especially if they are only going 50mm into the wood.
Have a look at the anchor bolts that window cleaners / maintenance engineers use when they’re on the outside of a building. Quite similar to car harness eye bolts.
In fact - look at the size of a seatbelt bolt - that should give you an idea of the strength you need.
Edited by Nigel_O on Friday 28th February 12:13
smifffymoto said:
I’m using fall restraint not fall arrest.
The arrest bit is if it goes to s
t,which it shouldn’t..
This is a last resort ,my prefered method is a webbing sling around the roof timbers or wire rope around a chimney.
I'm sure having half a chimney for company will be a great comfort on the way down.The arrest bit is if it goes to s
t,which it shouldn’t..This is a last resort ,my prefered method is a webbing sling around the roof timbers or wire rope around a chimney.
smifffymoto said:
I’m using fall restraint not fall arrest.
The arrest bit is if it goes to st,which it shouldn’t..
This is a last resort ,my prefered method is a webbing sling around the roof timbers or wire rope around a chimney.
That would be my preferred also, depending on what and how the timbers are fixed. When we have fall restraint systems installed, if in timber they’ll either have a saddle,plate to spread the load, or strapped over at least 2 joists.The arrest bit is if it goes to s
t,which it shouldn’t..This is a last resort ,my prefered method is a webbing sling around the roof timbers or wire rope around a chimney.
If the is was for myself, for DIY, I’d be hanging off four 8mm or 3 10mm and an absolute minimum, and checking out the substrate carefully. Not a chance I’d be hanging off 6mm’s. I’m all cases I’d prefer protruding studs and a double nut and shake proof washer set up.
Installing for someone else, I’d only do it to a detail from a Prosfessional with PI insurance or following manufacturers recommendations to the letter, exceeding them even.
Installing for someone else, I’d only do it to a detail from a Prosfessional with PI insurance or following manufacturers recommendations to the letter, exceeding them even.
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