Carbon fibre centre pole query

[Edward John M]

Every pyramid tent I have used [ and I have only used the Chouinard/BD Megamid] has failed because the centre pole snapped or bent.

I don’t use walking poles and my ski poles are needed for skiing.

I need advice on laying up a superior strength DIY centre pole if I decide to buy another ‘Mid.

I am happy to trade packed bulk and weight for strength in this instance.

I am also quite happy to go with longer section length to 650mm/ 700mm and I have the bottom adjustable section of several Megamid poles to use for height adjustment.

Suggestions for layering and diametre please Present thinking is for 25mm minimum and three layers, first and outer layer using diagonal sleeve with an inner of longitudinal lay sleeving

[JCH]

Several BPLers have posted on CF MYOG trekking poles and tent poles…you can search for more of these posts.  If it is any help here is my post on the subject wherein I made poles for my Duplex…these were inspired by Bob Moulder’s work.  The eBay CF tubing supplier mentioned in my post has proven reliable, cost effective and is selling a quality product.

I suspect the OD required will be smaller than 25mm, perhaps 18-20mm.  Even at 1mm wall thickness the large diameter tubes are extremely stiff.

Edit: Ruta Locura produces many poles and are, to my knowledge, well thought of.

[Edward John M]

Thanx for that link, the sellers prices are reasonable and you may be right in that 25mm may be strong enough when compared to 25 / 32mm Aluminium

[Bob Moulder]

It wasn’t easy to find the diameter of BD’s stock 75″ CF pole, but according to this review it is 18mm.

Personally I would go a bit larger in diameter than 18mm for a pole of that length, although 25mm seems perhaps a bit of overkill.

But maybe overkill is what you’re after.

How did the previous poles fail? 3K woven CF tubes are extremely strong in compression, and they can sustain a fair amount of side load flex without breaking.

[Clifford Deakyne]

One way to address this is to compare the moment of inertia of the various diameters assuming a constant 1 mm wall thickness out of the same material.  If the pole is set on the ground and the pole tip is in the tent then the likely failure from loading would be buckling allowing a simple comparison.

So relative to the 18mm OD,

20 mm would be 12% heavier with 40% higher buckling limit (“strength”)

22 mm would be 24% heavier with 88% higher buckling limit

25 mm would be 41% heavier with 180% higher buckling limit.

So you can decide how much extra weight your willing to take for the extra strength.

[Edward John M]

It seems as if CF poles are constant diametre, wouldn’t it make more sense to have the larger section in the middle of the pole where buckling resistance is needed most? That is how I made my last alloy pole I put 19mm section in the middle with 16mm sections at top and bottom and that seemed to do the trick.

I’ll happily trade weight for strength as 25mm CF is no heavier than the alloy poles that came with the megamid originally

The original megamid poles all snapped at the junctions between top pole and the next one down, when I strengthened the top section by using a thicker tube the next failure was at the junction of the second and third section and this storm was the one that killed the tent as the broken pole went through the fabric in a catastrophic rip top to bottom

[Bob Moulder]

Using different diameters complicates construction somewhat, but certainly it could be done.

Instead of ferrules to join the poles one could glue some stopper rings on the outside of the smaller pole.

However, comes a point (see Cliff D’s analysis!) that it becomes so strong that for practical purposes it doesn’t matter.

 

[JCH]

…It seems as if CF poles are constant diametre, wouldn’t it make more sense to have the larger section in the middle of the pole where buckling resistance is needed most?

Using different diameters complicates construction somewhat…However, comes a point (see Cliff D’s analysis!) that it becomes so strong that for practical purposes it doesn’t matter.

This is, after all, the $10,000 question…choosing the weight/strength/complexity of construction sweet spot :)  And is why building your own pole(s) is such an attractive proposition.

Please keep us informed on how you choose to solve the problem.

[Edward John M]

The link given for the Chinese made CF sections and the low cost compared to DIY really makes DIY a non-starter if the quality of the pre-made is up there. All that then remains is to make the choice about how strong the pole really needs to be at 4-5 * 500mm sections so 22mm seems to be a reasonable compromise at a 1mm wall thickness.

Next question is the the joining method, which internal tube is best in that application? that is how much clearance does the CF tubing need ?

[JCH]

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[Bob Moulder]

You could make joint ferrules from 20mm OD (18mm ID) stock. If I were making that pole for myself, I would make the joiners 6″ long, so that 3″ of the joiner would be glued into one section, with 3″ sliding into the section it mates with.

For a 75″ pole it seems 5 x 15″ sections would be the way to go. For maximum strength in a pole of that length, you really want the sections to fit together as snugly as possible, so do as little sanding as you can on the ferrules.

Join it all together with some 2mm shock cord. Anchor the shock cord with some balsa wood plugs saturated with cyanoacrylate (Krazy) glue, being extremely careful not to let excess glue run down inside the tube. (There’s a story behind that….) Installing shock cord can be a bit tricky but you’ll figure out a way to use a clamp or a clove hitch around a bamboo chop stick to give yourself some working slack.

What you do with the tips is another chapter.   :^)

[Edward John M]

Hey Bob.

I always thought that the longer the section the better and I have no trouble at all with 500mm modules even with the ferrules adding extra. Using them as factory cut length just seemed the best idea

All of my packs are tall enough for the pole bag to slip in vertically internally or safe on the outside

22mm seems the best compromise and as a bonus the adjustment section is 25*1mm so a 22mm fits that easily.

May only get used with the tarps in the short term,

[Bob Moulder]

OK, keeping in mind that with the 3″ addition for ferrules the 15″ sections would fold down to 18″ (457mm)

This assumes you want a 75″ assembled pole. Of course, “rolling your own” you can make it whatever length or number of sections you like.

[Nick Gatel]

Edward,

I have owned a Chouinard since the 80’s and still use it occasionally. The pole is still good and it has survived some serious desert wind storms (I have an extra pole set I bought years ago and have never needed it). Just curious what the conditions were that cause the breakage… don’t take this as criticism.

I don’t use trekking poles and use mids for almost all my trips; currently a Deschutes CF and a Trailstar. I use .600″ diameter carbon fiber poles I bought from Ruta Locura (not cheap) and they have held up well with almost no deflection. I have used thinner carbon fiber poles with other mid shelters in the past and although none broke (.292″ and .450″) there was too much deflection and I lacked confidence in them. The .450″ pole worked well with my Hexamid, but I didn’t like it in the Trailstar.

[Edward John M]

One of those sudden Alpine gusts of wind you get above 1550m in Victorias Bogong High Plains area that hit after a reasonable snow fall.

I admit to partial operator error as I’d not yet woken up enough to get out of the pit and clear off the snow, actually felt like it may have been a microburst .

The other was when we had two Megamids door to door and a big diamond tarp stretched between them, my ‘mid was on the windward side and again one of those massive gusts of wind, that tho was probably excessive strain due to our usage but we do use that configuration a lot

This was my third Megamid, UV kills them in about 10 years.

My original Chouinard is in the Patagonia store museum in Torquay now along with some other old climbing gear/tents/clothing

[Nick Gatel]

Yeah, with any mid it is important to keep equal tension on the pole from all guylines, which is sometimes difficult in snow + wind.

The PU coating on my Chouinard is starting to degrade. I have a plan to bring it back to life, but it involves using my wife’s washing machine so I have to wait until she is gone for a few days and I am left at home unsupervised. I only put up a shelter in poor weather and it never sits out is the sun during the day, so my shelters don’t suffer much from UV exposure. The one exception is my first tent that I bought in the 60’s. I should get rid of it since I don’t use it any more. But I’m a pack rat.

One thing I see a lot here on BPL is people looking for shelters with a minimal amount of stakeout points, flimsy Ti stakes, and itty bitty guylines. I went that route for a short period of time, but am back to long sturdy stakes, heavier guys, and as many stakeout points as possible.

 

[Edward John M]

Southern hemisphere UV is much higher than Northern

[Andrea C]

If I was to use a single pole, would use a 12×9 (1.5mm thickness) or better a 15×13 (1mm thickness), the 100-120cm length required is enough the create too much flex.

I can confirm the quality of the carbon tubes supplies by the shop mentioned above, I’ve made an A-Frame for my Trekkertent, and quite happy with.
As it’s a triangular shape, is not subject to compression as a single pole. I’ve used 12x11mm tubing and 11x9mm short pieces for the joining inserts. The tubing is so well made that fits snug, no play, in fact it is airtight!
The top “V” piece is made with alluminium tubing, I’ve beefed up this part as it takes most of the strain: can’t get it to flex by hand.

[Edward John M]

Nice. What section length? 500mm?

[Andrea C]

Each side is 122cm long and is formed of 3 sections 40cm long, two of those sections have 4cm of joint sticking out, so the total length when packed is 44cm and about 5-6cm diameter of the bunch. It can be easily strapped under the top-tube of the bikes.

Once unpacked and joined, each 122cm side is added to a  tip which is about 5-6cm, and the two sides join in the top “V” which adds another 8-10cm.
In total is about 138cm per side, which makes the A-frame 120cm tall and 120cm wide. This gives great freedom and use of the tent.

[Edward John M]

Reminds me of my old boy Scout monkey coffin but taller in front.

This project may have to wait a while due to lack of discretionary funds in the short term

[Author]

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