UKH

Be gentle. I'm new here

I just wondered if anyone had any thoughts or force comparisons of pressure applied to bolts placed on the TOP of a rock (i.e. rock surface is horizontal with Petzel Coeur bolts drilled and fixed DOWNWARDS) for an anchor set-up with cordelette/slings going over the edge (with protection) and then down vertically. I don't have a picture but hopefully that is pretty clear.

Does this set-up put undue pressure on the bolts and does the downward force act in a pull-out or downwards direction on such anchors? I can't get my head around it. Should have listened at school LOL!

The horizontal force from the sling is going to be in an equivalent direction to a downward pull on a conventionally positioned bolt, so it would be fine as long as the bolt is well placed in the first place. Not entirely uncommon to see bolts in horizontal rock e.g. at the top of Southern Sandstone.

It will be subject to lower force than about placed over the lip as the friction from the sling at the edge, and the edge it self will take some of the load.

Where are you planning to place these bolts?

Quite a few placed like that at various crags where theres no natural protection options. Also lots of bolts placed like that at the top of cave / pot hole entrances before a rebelay a bit further down inside. 

Different but you can also place I've screws like that i.e. in a crevasse rescue 

Having said that, direction's almost irrelevant anyway as a well placed bolt is plenty strong to an outward pull as well.

Just don't put them where children playing by the edge might trip over them

That's what I thought but just wanted some reassurance from wiser (if not older LOL!) heads. Thank you all. Looking forward to a browse around the forum posts here

Thanks for the reply. I imagined the edge acting almost like a shelf taking some of the pressure/weight.

A lot of the removable anchors are intended to be placed this way (as well as in vertical settings), I've placed them like this in concrete. As others say... if the load completely horizontal on a vertically placed bolt, it's equivalent to a straight down pull placed in vertical rock.

If you are looking at using Petzl Coeur Pulse, more important considerations are the holes. These have to be really very round  (that means using a "cross head" 4 cutting tip drill not a standard 2 cutting bit drill bit) and get the exact diameter so don't think a 1/2 inch drill and a 12mm drill are close enough + make sure you brush the holes clean. This is really *important* with the Petzl ones the holes have to be just right!

If you haven't already bought them yet, you might also consider concrete screws, those can be pretty strong too (and a lot cheaper), but you do need a spanner/wrench to place and remove then

For your viewing pleasure...

youtube.com/watch?v=eZ3QVTX75rg&

p.s. holes are permanent damage. Only drill when necessary. Not trying to open that can of worms, just saying...

When they are tested for certification it's entirely up to the testing facility how the do it, normally it's horizontally because that's how the machines are set up but pulling upwards is fairly common, my test rig does it that way. It's called radial testing by the way.

I'm probably missing something, but I've never understood this: it seems to me that any shape which rotates will produce a round hole .... no?

As others have said the orientation horizontal or vertical doesn’t make a whole lot of difference. That said, edge distance could be an issue if you go too close. In perfect rock 150mm edge distance would be an absolute minimum that I’d not be super comfortable going down to. Without seeing the site it’s hard to say what edge distance is reasonable for the rock in question but I have thought you’d want to be around 500mm back from the edge which would allow 120cm slings to drape over the edge nicely.

It would be kind if you could reassure the thread you aren’t bolting in an inappropriate place i.e. on top of an established trad route and an established trad crag or some suchlike…

I think what CCT is saying is more about the diameter and shape of the hole.

Also sds bits drill by hammer action rather than rotation. A chisel bit could cut an oval hole if the rotation speed synchronised to the hammer action, a cross bit more likely to cut circular.

No, there is a thing called a Reuleaux polygon which can be a triangular hole produced by a two-fluted drill most commonly used in engineering to drill square holes using a special drill chuck (called an Oldham chuck). A hand-held drill will normally produce a triangular hole and that's what happens in rock, the actual drill bits are oversize ( a 12mm bit is around 12.7mm across the cutters but you won't get a 12mm rod into the hole). The four-cutter bits give rounder holes but drill slower.

Thanks for mentioning Jim. I was tempted to go there as my inner nerd finds the various shapes fascinating and how it precesses making a spiral into the hole. But I thought that was way to nerdy to mention, so glad someone else did 😄

Thank you, you've explained this much better than I would have. I've drilled many triangular holes in blockwork walls using cheap drill bits. Nylon plugs don't mind but they're not so good for sleeve anchors.

Better than I could explain it either! I would have just thrown the link https://en.m.wikipedia.org/wiki/Reuleaux_polygon and run away.

If people look at the Reuleaux Triangle, the key/surprising thing to note is that the shape has constant width, which is exactly how a flat blade (2 cutting tips) can make this rounded triangle. You'll also spot a cross shaped (4 cutting tip) won't cut a perfect circle either but more like a 50p shape, but that's a lot closer to a circle than the triangle. 

I was once told that when you look at (blasting) shot holes in rock in historic  mines and quarries, you can tell the difference between hand drilled ones with a jwmper (jumper) because hand drilled holes are triangular but machine drilled ones are perfectly circular. I don't think they looked closely enough because the machine drilled ones are a bit triangular too, just less severely Reuleaux Triangles. Sorry everyone, I feel part responsible for a bit of a digression here.

Let's just accept that a 4 cutting tip drill bit is mandatory for the petzl removable anchors!

If you watch the video linked in this thread, you will see that placing fixed gear on horizontal surfaces is a bad idea (watch to the end).

https://www.ukhillwalking.com/forums/rock_talk/has_uxbridge_road_ever_had_a_se...

Thanks for the replies. I'm now wondering whether a crosshead bit is also a better choice for holes for normal expansion bolts, or whether a chisel bit is good enough: the holes I've drilled (in limestone) using the latter certainly look circular enough.

IMHO, if they look circular and you are using wedge/expansion bolt or glue in, that's good enough. It's really the Petzl Coeur ones (and some other removable ones) that are really fussy here because their wedge mechanism has a very limited expansion range.

Normal (2 cutting tip) drill bits are cheaper and easier to source than cross head (4 cutting tip) and drill more quickly/less battery in harder rock because the energy of the hammer isn't "diluted" across 4 tips.

However I defer to any advice jimtitt may give as he's the forum's resident bolt expert