Concrete screws.

Chocolate fireguard

Active member
(y)
Any idea why the spread of the FBS results (12.9% of the mean) is much greater than that of the MMS ones ( 2.5% and 1.9% of their means)?
It doesn't seem to be due to  1 or 2 outlying results, although I do appreciate that it's possible to read too much into 6 tests on each size.

 

SamT

Moderator
nobrotson said:
Nice one. Do you need to use a washer with them when installing caving hangers? I assume yes...
No I dont think so. Why would you out if interest? Just curious.
 

SamT

Moderator
Types:

Plain washers, which spread a load, and prevent damage to the surface being fixed, or provide some sort of insulation such as electrical

Spring washers, which have axial flexibility and are used to prevent fastening or loosening due to vibrations

Locking washers, which prevent fastening or loosening by preventing unscrewing rotation of the fastening device; locking washers are usually also spring washers

Only one you might consider is a locking washer I guess but Im pretty sure the touque and friction on the bolt is enough to prevent the bolt unscrewing
 

Pete K

Well-known member
We've used nylon washers where the screw anchors are used with stainless plates in damp areas. They will be stripped out eventually and resin anchors placed instead but it's nice to know there won't be any nasty mixed-metal corrosion in the mean time.
 

pwhole

Well-known member
I always use nylon washers with screwbolts and hanger plates now (probably the 'we' Pete's referring to!), as the bolts are always zinced in some way and the plates are always stainless. Most of the long-term maillons we've left in explorations eventually rust at the contact with the stainless. That said, I hung off two hangers on Tuesday that I installed two years ago with no washers, in a wet spot, and there was no evidence of any rust at all at the contact point. I wasn't able to unscrew them to check inside, but others I've left in long-term haven't had any at all.
 

Mattrees

Member
Thanks Simon,

That's really useful.

I'm using the 7.5 X 50 Multi Montis to maximise drill life. If you are doing any further tests would you mind testing a batch of these shorter anchors? I could post you some samples.

I'm expecting they would give similar figures since the file is the anchor strength rather than the rock.
 

Simon Wilson

New member
Mattrees said:
Thanks Simon,

That's really useful.

I'm using the 7.5 X 50 Multi Montis to maximise drill life. If you are doing any further tests would you mind testing a batch of these shorter anchors? I could post you some samples.

I'm expecting they would give similar figures since the file is the anchor strength rather than the rock.

I think you're probably right. Send me some and we can find out.
 

MarkS

Moderator
Super piece of work, and I hope it marks the beginning of the end for the use of throughbolts in caves. A big thanks for doing it and for writing it up.

I used some in anger for the first time this weekend.  (y)
 

SamT

Moderator
I feel a little saddened that its taken this long for them to catch on!!

https://ukcaving.com/board/index.php?topic=6897.msg93205#msg93205
 

Wayland Smith

Active member
When installed correctly these are not torqued very high.

What needs to be done to prevent unfamiliar users of the rigging giving the bolts an extra tweak
"to make sure they are really tight."
Thus over stressing them with the risk of failure.  :-\
 

Simon Wilson

New member
Wayland Smith said:
When installed correctly these are not torqued very high.

What needs to be done to prevent unfamiliar users of the rigging giving the bolts an extra tweak
"to make sure they are really tight."
Thus over stressing them with the risk of failure.  :-\

Overtightening is a thing that a few inexperienced people have always done. I've come across bolts in Spits that have been greatly overtightened. I've even heard of people shearing them off by overtightening.

My advise to anybody wanting to use concrete screws is, if you have any uncertainty about how much to tighten them then do not use them until you have found out. They absolutely do not need to be and should never be "really tight". They should be tightened the same as a bolt in a Spit which is very lightly.
 

Mattrees

Member
droid said:
Is that sump drain bolt tight, ie nip up by hand then a quarter turn?

In my experience they won't cut a thread using just fingers (unless your fingers are much stronger than mine!). You need a spanner to place them, not just to nip them up at the end.
 

SamT

Moderator
On the other side of the coin.. I gave some 8mm ones to a mate to equip a new climbing  route at Kinsley. The idea being to trial placement then replace with resin bolts whrn the route had been worked and the most ideal clipping points fine tuned. 

He came back saying the were shit and that he'd sheared a couple trying to get them to cut a thread.  I suspect the limestone there is bullet hard compared with the peak limestone 'cheese'. 

I've certainly struggled to get them to cut into hard red brick and sheared one.
 

braveduck

Active member
Use them a lot in the garden/house. The secret is drilling the hole the right size ,
running drill in and out several times and making sure the hole is clear of dust.
If it gets tight when going in ,remove and and run the drill in and out a few more times.
I think they are brilliant.
 
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