Concrete screws weren't really popular at the time so we never had that discussion, but from my point of view I can't stand them (concrete screws, not necessarily the French!). I find them to be time-consuming to install & remove, way too awkward to use for serious climbs, don't sit in a hanger whilst racked on your harness, holes often need boring out in hard rock, and it's quite easy to damage the flutes which means they're not necessarily that reusable. For the UK I can certainly see their place but I don't get how deep Alpine projects like them as speed is of the essence.
I was with a team that started using concrete screws in Huautla in 2018, re-rigging the early pitches of Agua de Carrizo which, back in the day, ie in 1978, was rigged the old-fashioned American way, that is, by tying a length of Bluewater or PMI to a natural belay, then abseiling down. After a couple of trips we started to notice that several screws on the first two pitches - 35 and 110 metres, with multiple rebelays - were just pulling out. The rock, it seemed, was too soft, or in some places, too brittle. Bloody terrifying. We binned the lot.
I used the same 8mm Hilti bit for over a year and drilled many, many holes - I lost count, but probably a couple of hundred, and I only retired it as I thought I probably should - I had several new ones! I think it was about double the cost of a normal bit, but probably about ten times the lifespan
Apart from one throughbolt that I didn't install. And now it's there for ever - in the wrong place!
Quote from: pwhole on November 19, 2020, 10:46:42 amApart from one throughbolt that I didn't install. And now it's there for ever - in the wrong place! pwhole's remark above interested me - and prompted me to ask a question which may be viewed as a slight digression (for which I apologise in advance).I have a need to remove a particular Throughbolt, so I've been wondering on how this might be done. I know that overtightening the nut causes the a Throughhbolt to start creeping out of the hole but removal in this way is not possible because the thread is not continuous to the bottom of the bolt. I'm wondering about using a few larger nuts to act as spacers so that the unwanted Throughbolt can be extracted fully using its own thread. Do folks reckon this will work? Also, would this compromise the safe re-use of the same hole with a future replacement Throughbolt (if it results in wear to the sides of the hole during extraction)?(The consensus might also help pwhole solve the problem he mentioned above.)
...With a decent sized spanner or breaker bar and socket (more doable in 13mm) it will either come out or snap. If it snaps, hammer it back in until it is flush. Maybe leave it alone after that either way unless you are desperate, otherwise maybe drill it out to the next size up?
pwhole's remark above interested me - and prompted me to ask a question which may be viewed as a slight digression (for which I apologise in advance).I have a need to remove a particular Throughbolt, so I've been wondering on how this might be done. I know that overtightening the nut causes the a Throughhbolt to start creeping out of the hole but removal in this way is not possible because the thread is not continuous to the bottom of the bolt. I'm wondering about using a few larger nuts to act as spacers so that the unwanted Throughbolt can be extracted fully using its own thread. Do folks reckon this will work? Also, would this compromise the safe re-use of the same hole with a future replacement Throughbolt (if it results in wear to the sides of the hole during extraction)?(The consensus might also help pwhole solve the problem he mentioned above.)
I think Simon Wilson tried the above technique with little success. I think that if you want an anchor to be removable, don't place a through-bolt.
Quote from: MarkS on November 23, 2020, 10:03:31 pmI think Simon Wilson tried the above technique with little success. I think that if you want an anchor to be removable, don't place a through-bolt.I agree, but Pitlamp was asking for a technique for one particular placement, already installed. No evidence of Simon having removed one of those type of sleeved through bolts on his page. Lots of very similar videos online from the states using the same technique, generally looks pretty straight forward and successful. I think the key is probably the hydraulic puller they are using and also using something that you can 'pull' up on, whilst spinning the bolt. i.e. just a socket spinning the bolt isn't going to allow you to pull up on the bolt which is what causes the requisite groove to be cut in the cone.
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