Making and testing rap rings

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Banquo

climber
Amerricka
Topic Author's Original Post - Feb 22, 2014 - 09:01pm PT
Aluminum raps rings only cost $2-$5 apiece and I really don't use very many but I thought I'd figure out how to make some cheap ones anyway. A waste of time that perhaps only makes sense since I have the tools make them and the means to test the result.

I went on Ebay and found a 24" long piece of aluminum tube. OD is 2.5" and ID is 1.5". It is marked as 6061-T6 a low strength alloy that shouldn't corrode too bad or suffer too much from fatigue or other cracking. With shipping it cost $40.78.

I cut a 3/8" piece and because I have a lathe, I smoothed up the two cut faces and got it to 0.375". Then I rounded over the inside and outside edges with a normal wood router. I loaded it up to see what would happen. It seemed very stiff up to maybe ~3500 lbs (~15.6 kN)so first yield should be something less than that. Aluminum doesn't have a well defined yield point like steel and residual stresses will also influence first yield. It came apart at 5170 lbs (23.0 kN).

I pulled out Roark's "Formulas for Stress and Strain" to figure out how to calculate the stresses and based on a yield of 40,000 psi, first yield should be at about 1760 lbs (7.8 kN) for the 3/8" ring.

I've decided to cut them 1/2" long so the predicted first yield should be about 2400 lb (10.7 kN). I estimate it will break at slightly more than 1-1/3 times the 3/8" one so maybe it will break at about 7200 lbs (32.0 kN).

The first one I cut on the horizontal band saw but I cut the second one on the power miter saw with a carbide blade which was noisy but worked fine. The edges were rounded over with a woodworking carbide router bit which also worked just fine. The worst part is cleaning up the fine aluminum chaff.

Allowing 1/8" for the saw waste and no cost for tools or time, each ring is $1.06. A cheaper source for material might be found.
6061/T6
6061/T6
Credit: Banquo
3/8" thick ring
3/8" thick ring
Credit: Banquo
Loading setup. Big router gouge in one side.
Loading setup. Big router gouge in one side.
Credit: Banquo
5170 lbs
5170 lbs
Credit: Banquo
Roark
Roark
Credit: Banquo
ruppell

climber
Feb 22, 2014 - 09:13pm PT
Sick work. When I first read this I thought of hollow alumi rings. I'd rather rap off a dead tree branch then one of those bad boys. But seeing as how your cutting them out of solid aluminum I'm fairly impressed. I would rap off of one of yours before a dead tree branch for sure. How fast would solid alumi where though would be on of my concerns. I go through a lot of belay biners each year so I know the answer. Have you tried to do the same tests with steel? I'd be curious to see the comparison.
bhilden

Trad climber
Mountain View, CA/Boulder, CO
Feb 22, 2014 - 09:17pm PT
Carry rap rings is just an excuse for failure:-)

Seriously, cool test. It has been my experience in 40 years of climbing that items that aren't locked down seem to disappear over time. So, having a cheap source of reliable rap rings reduces the anguish when you go back to a route where you put two new rings only to find them gone.

What do they weigh?
ruppell

climber
Feb 22, 2014 - 09:20pm PT
Carry rap rings is just an excuse for failure:-)

LMAO. I almost posted a very similar statement. Then I remembered I've rapped off a ten dollar biner or two. But yeah rap rings are pretty last decade. lol
Clint Cummins

Trad climber
SF Bay area, CA
Feb 22, 2014 - 10:06pm PT
From touring the Valley obscurities, I have scored a lot of those SMC hollow aluminum rap rings. One of the nice things about them is they are very light.
They test to a very high load also.

It wouldn't be a good idea to toprope through hollow rings with a dusty rope, though. I saw a ring with a hole worn in at Smith Rock some years back.

I have found a couple of the Omega Pacific solid rings, too. But they are quite a bit heavier than the SMC, and the SMCs are plenty strong, so I'd never carry them.
Banquo

climber
Amerricka
Topic Author's Reply - Feb 22, 2014 - 10:08pm PT
These are beefy monsters, the 1/2" one weighs 64g.

I have a climbing buddy who has become interested in canyoneering and I have been going on some trips with him. Rappelling, rather than climbing, uses significantly more rings. I'd post trip reports but this is a climbing forum not a descending forum.

Also, sometimes after a FA we have to figure out a descent which will require rings. FA's often seem to require leaving rap stations.

Cragnshag and I left some rap stations behind to enable descending out route "Buffoon Dome" on the central west face of Balloon Dome. That one probably deserves a trip report but the story seems to lack the valuable component of humor.
ruppell

climber
Feb 22, 2014 - 10:24pm PT
Clint

I get your point but at that point why not just rap from webbing? No climber in their right mind would ever TR off it. Hence my previous post about the hollow alumi rap rings. LOTS of climbers rap and TR off those relics. I'd rather have them donated to the OP so he can melt them down and make some solids out of them.
Ghost

climber
A long way from where I started
Feb 22, 2014 - 10:26pm PT
I'd post trip reports but this is a climbing forum not a descending forum.

Dude, this forum descended into the primeval mud a long time ago. A trip report about canyoneering would lift it significantly. Post up.
Banquo

climber
Amerricka
Topic Author's Reply - Feb 22, 2014 - 10:56pm PT
An interesting thing to me, or something I learned, is that while elastic, the maximum stress in the ring is at the load points. The load points are where the rope touches the ring. I had assumed that the maximum stress would be at the 90 degree point where the fracture occurred.

However, after the ring elongates, the maximum stress is more nearly tension than bending at the 90 degree point and that is where it breaks.

When elastic, the critical section is at the top and bottom. When plastic, the critical sections are at the left and right.
ruppell

climber
Feb 22, 2014 - 11:12pm PT
Banquo

What? You lost me there. Pics would help I'm sure. Are you saying that the break point was on either side of load? If so that is what you would expect isn't it?
speelyei

Trad climber
Mohave County Arizona
Feb 22, 2014 - 11:30pm PT
More canyoneering, less socio-political diatribe. Post!

Cool rap rings you've made. I just cut links off of chain with an angle grinder...
pyro

Big Wall climber
Calabasas
Feb 22, 2014 - 11:43pm PT
Touches? Awesome craftsman with tools that make him who banqo is. Thanks for the share. Top rope solution is not solved but man what a show!
T H

Boulder climber
extraordinaire
Feb 23, 2014 - 12:21am PT
The cuts/ burns on the work table speaks volumes.
JimT

climber
Munich
Feb 23, 2014 - 03:47am PT
Have you tried to do the same tests with steel? I'd be curious to see the comparison.

Making stainless rap rings that way would be a financial disaster. Hollow stainless bar is very expensive so the material cost for a 1/2" ring would probably be $20 before you started machining it though here are companies who make rings for sealing flanges by forging sections of it (at a price!).

Once you start machining then it would actually be cheaper to make aluminium rings from flat bar if material costs are the only consideration but rolling and welding will probably always be the cheapest if labour is priced in. A 2.5" ring in 1/2" stock costs about $0.60c for material alone and somewhere around 20 per hour is easily achievable.

Strengthwise alloy rings are plenty strong enough as rap rings though much weaker than a stainless ring, a 10mm welded ring gets about 82kN and a 12mm one over 120kN (the limit for our tester).
Weight wise you might as well replace a 1/2" solid alloy ring with an 8mm stainless one, its twice as strong, better corrosion resistance and lasts longer which is probably why in Europe the whole idea of alloy rap rings is virtually unknown, Ive never seen one in over 40 years climbing!
tradmanclimbs

Ice climber
Pomfert VT
Feb 23, 2014 - 09:36am PT
Why not simply use a cheap screw/quick link?
Spider Savage

Mountain climber
The shaggy fringe of Los Angeles
Feb 23, 2014 - 11:12am PT
^^^^ Duh!

I have several store-bought aluminum rap rings that I've been carrying around since the 1970's. For some reason I've never used one. Now they are antiques and too dear to abandon.

I have used the quick-links from the hardware store. They are abundant, cheap and satisfactory. Will last longer than the webing or perlon left to the anchor.
Banquo

climber
Amerricka
Topic Author's Reply - Feb 23, 2014 - 11:20am PT
Are you saying that the break point was on either side of load? If so that is what you would expect isn't it?

Yes. If you look at the last picture (diagram from Roark), Point A is where the highest stresses are when the load is less than the elastic limit. When the load is less than the elastic limit, A is in pure bending while B is in combined bending and tension. It breaks at point B after it has elongated into an oval.
RyanD

climber
Squamish
Feb 23, 2014 - 11:24am PT
This is cool stuff banquo!

Nice work!


A canyoneering TR would be awesome too, don't be shy. This isn't really a climbing site I've heard before many times on stupid non climbing threads. It's a site for climbers apparently so let er rip!
Banquo

climber
Amerricka
Topic Author's Reply - Feb 23, 2014 - 11:56am PT
Have you tried to do the same tests with steel? I'd be curious to see the comparison.

Making steel rings is much harder to do. I would have to cut it in the horizontal band saw which is slow and I would have to radius the edges in the lathe which is hard to do a nice job of. I can make an aluminum one in a couple minutes but a steel one would take several times as long. Steel pipe does come in something called Double-Extra Strong (AKA XXS) and schedule 160. These are usually low grade mild steel and yield strength is probably less than the 6061/T6 but ultimate would be higher.

1-1/2" XXS pipe has an OD of 1.90" and a wall thickness of 0.40". ID is 1.10". If the yield strength is 30 ksi (A106 grade A) and the cut length is 3/8", the first yield would be 850 lbs. Failure would be pretty high because mild steel is ductile and may strain harden. If I did the calculation right, it would weigh 0.225 lb or 100 grams. Heavier, smaller and not as strong but much more wear resistant than mine.

2" XXS pipe (OD 2.375, ID 1.503) cut in 1/2" length in a higher grade steel might be adequate for toprope rings but I have no interest in making any.

For steel, I use chain links. Carbon steel chain is cheap and readily available. I picked up two 6 foot pieces of 3/8" stainless steel chain on Ebay for $50 with shipping and cut them up. The seller had mis-priced them as they are now going for $80 each. I use them for belay anchors not rap rings or toprope rings.
Steve Grossman

Trad climber
Seattle, WA
Feb 23, 2014 - 12:52pm PT
Aw, just use five wraps of tie wire and a little cloth tape like Layton Kor used to do to save a little scratch. I wonder what one of those would test out at? LOL
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