Elbows for carbon tent poles

[R]

Hey all,

I am interested in making a tent using carbon arrow shafts for poles, and need a solution for the elbows.

I’m looking at the Vforce line of arrows from Victory, per Caffin’s recommendation (scroll to bottom for size chart).  For the elbows, I’m thinking of using Easton 7075-T9 aluminum tent poles as an outer sleeve.

A couple questions:

1. Can that alloy be safely bent for this purpose? (Will I need to fill it w/ sand to prevent crimping?)
2. Would this be a reasonable bending tool?
3. What ID/OD clearance should I aim for to get a good fit?
4. Any suggestions for stoppers to prevent the poles from jamming inside the elbows at the bend?  Something to withstand the compressive loading?

 

 

[Roger Caffin]

Hi Rene

I recommend the VForce 400 size. OD of ~7.4 mm, and a very useful ID of ~6.2 mm. This lets me use 1/4″ ERW SS tubing for an internal elbow. I suspect the VForce 400 uses a ground-down 1/4″ mandrel for forming, but I might be wrong.

You will want the Easton 2117 (I think) arrow shaft to fit snugly over the CF tubing.

No, that 7075 T9 alloy can NOT be bent the way you want. It is too hard. All that bender will do is crack and destroy the tubing.

Clearances? ‘A snug fit’ is good, typically <0.1 mm, preferably <0.05 mm. You are into the lathe and micrometer territory.

Yes, you WILL need to prevent the ferrules going inside the CF tubing from jamming. I use heavy heatshrink as a buffer:

Email me direct for further info if you wish.

Cheers

[Les Waddel]

So… I’m making a dyneema tent and this is my solution for the short end of the tent.  That is 1/4″ woven CF tubing.  Wrap shrink-tite around the vertical ‘arrow’, insert high density foam (blue) shaped to fit into both arrows to give desired bend, slip woven CF over both, wet out with epoxy, slip heat shrink tubing over, heat it to compress… a few hours later (or put in a hotbox for an hour).  Top tube is 10″ both vertical/side poles are 22″ total weight is 1 oz.

[Sam Farrington]

Rene,
The 400 on the Victories is a measure of the stiffness. To make them stiffer, they must use a thicker walled tube, which is therefore quite stronger, based on my break testing.  Unless Victory has changed its marking system, the stiffer poles have a lower number (350 & 300), signifying less deflection over a given span.  So the 300s tested much stronger in break tests, and are only a grain or two heavier per inch.

There can be confusion about the Victory models and their names – Look for a reference to  V Force V6 in the name.

All the above mentioned Victory shafts, including the 300, will fit snugly into the Easton .344″ OD Nanolite alloy tent tube, which can be cut and polished into external ferrules. The tube is available from Quest Outfitters  (There are also other options for internal ferrules.)  The snug fit is important, because if the poles are allowed to go into an only slightly oval shape when stressed, they break with less pressure.

Quest only has elbows for the .340″ OD poles. They say that they fill fit the .344″, but unless you want wobbly elbows, that is not so. The elbows are also quite heavy, because the ferrules run right through the elbow and protrude from each end. They also do not seem to be suited for boring.  They do not fit the Victory poles.

There are elbows sold by Fibraplex, but they can be bent by hand, and do not hold an angle well.

Also, your tent design may require a differently angled elbow than those which Quest offers.
The .344″OD tube can be bent with heat; however, the heat will destroy the high temper of the resulting elbow, and it will not hold the angle. Done that.

So you can see one reason why Roger uses the stainless steel bent exactly to the angle he wants. One other option is to bond plastic end tips into on the V300s, then extremely carefully bend a section of Ti tent peg to your desired angle, and bore the end tips to accept the Ti elbow. This actually worked well for a prototype, and is shown and discussed at:

https://backpackinglight.com/forums/topic/45631/

Another option is to find a less tempered but thicker walled alloy tube from online metals or wherever that fits over the Victories, and bend it with the tube bender shown in your link.  Have bent some older A-16 pole tube with heat and they have held their angles, so know it can be done.  Don’t know if the bender shown in your link will cold bend less tempered alloy, and how much angle you are looking for.  If it is a slight angle, and the alloy is less tempered (6061-T6 can be found on line), you should be able to avoid crimping with your bender using fine sand from big box stores packed tightly in the tube and capped.  From my experience, a more expensive bender for 3/8″ OD from Ridgid will hold up better than the one shown in your link.

The final option for me was to order some polypropylene US Plastics equal angle Wyes that project from a small disc, and cut off one Y, leaving a 120 degree elbow that fits over a Gold Tip carbon shaft that is a little stronger but only slightly more flexible than the V300 shaft. The slight flexibility of the polypro elbow should absorb severe wind gusts and return to form in lieu of breaking the carbon. Only problem is must design around the 120 degree angle, which happens to be OK because that was the angle used for the Ti elbows. So moved on to other design issues and explored elbow sourcing no more.

Another option for you might be to use the Easton carbon poles from Quest that fit the alloy elbows for the .340″OD tube. This is a slightly heavier carbon tube than the arrow shafts, but still lighter than the Easton .344′ OD Nanolite tube, which is their lightest alloy tube suitable for tents. And you would probably have a stronger carbon tent pole (with alloy elbows) resulting. But again, the angles are limited, to 125, 145 and 90 degrees.

If you want to bend your own elbows, hope Roger can fill you in on the stainless bending. If you find or develop other options, please post them. Thanks.

P.S.  Just read Les W’s post.  Awesome!

Please note that some corrections were made to the above, and were not posted until after several hours after the initial post.

[Roger Caffin]

Yeah, that’s why I went to SS tubing: I could machine it to fit and bend it to suit. But I had to make a special tubing bender with a calibrated bend-angle protractor to do this without collapsing the SS tubing.

Now, woven CF tubing … WOW. The possibilities!
SOURCE??? Please.
What we now need is a soft rod which can be bent to the required angle to act as a former – something which can be dissolved out (or similar) afterwards would be nice. I WANT!

Cheers

[Samantha R]

Roger,

Soller Composites ( https://www.sollercomposites.com/index.html ) carries braided CF tubular sleeving in a wide range of sizes… also unidirectional CF sleeving and braided sleeving of other materials.

 

— Sam

[Roger Caffin]

Soller: useful.
I note that the tubular material has a wall thickness of only 13 thou (0.013″). I think this means you would need several layers of it to get a strength similar to the Cf tubing. That seems reasonable to me.

Busy today, but working on this idea to see if it could be made ‘home MYOG compatible’. Should be.

Cheers

[Edward John M]

I have never made UL tent poles but I can say that there is a lot of wriggle room when using the Soller sleeve. The way it is woven allows you to compress or stretch the sleeve by up to 50% in either direction but it does unravel very easily as you can see from the photo in Les Waddels post, other than that it is easy to work with. Use painters masking tape over the sleeve when cutting it

 

[Les Waddel]

Sollar is good, I believe that is where I got my roll of CF webbing sleeve.  On the pole in the pic I applied two layers.  I regularly use high density foam (XPS) for my forms.  It can be dissolved by dripping a bit of acetone in the tubing when cured.  So if you want a curved pole just cut the foam with a mat knife, shape it with sandpaper slide the CF sleeve on, wet it out, let it cure.  Compressing it and heat curing works GREAT.  If it is a straight piece, use heat shrink, if it’s curved…wrap it with electrical tape with the shiny side in/sticky side out.  It leaves little ridges on the finished piece but that is easily cleaned up.

Here is another site:  http://www.cstsales.com/a-carbon-fiber-material.html

[R]

Sam,

Thanks for the details.  I’ve been clicking through the same sites.  I found a .305 ID 6061-T6.  I could go w/ the Vforce 300 (.304 OD), but that’s 18% heavier than the 400, which should be strong/stiff enough.  I may try to shim the .295 ends of the 400 with foil/epoxy to fit the .305 ID.

Les,

Very interesting!  Did you do any explicit strength testing, or just arrive at a good-enough state?  With your small hoop, I imagine you’re not too worried about the strength.

This is for my lateral tunnel tent concept.  The poles will be ~12′ long, with three elbows ~140d.  With such a big hoop, I’m keeping a close eye on material strength.  If I go this route, I might try two different size braids – the larger one will lay the fibers closer to parallel length-wise, while the smaller will be closer to parallel around the circumference.  I think the arrow shafts alternate 3 layers in a similar pattern, axial-wrap-axial.

Some 3D print filaments can be dissolved in common solvents.  If some one wanted to get a lot more precise about things, this could be a good way to go.  For sharper angles, you could put a web across the elbow for a big boost in strength.  Print a re-usable, external form to compress it.

[Les Waddel]

Rene – No testing, I figured the poles where going to be under tension from the Dyneema and with double layer CF should hold up to pretty rugged weather that I would probably never be out in.

The front poles for the tent are my hiking poles (CF golf clubs 5 oz. each) and the middle support (support is .8 oz.)

[Author]

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