I'm thinking about trying my hand at making a Roger-Caffin-style tunnel tent to replace my Double Rainbow that comes on the majority of my companion backpacking trips - the idea being to get something a little bit lighter, but more importantly, more weather-proof and with better interior space.

I've already done a fair bit of design work in SketchUp and have what I think is my final design. My immediate concern right now is the pole system. I'm planning on using carbon fiber tubes for the poles, but these will require elbow bends at each join because of the tight radius of each hoop. Looking around online, I can only find 45 degree elbow bends - does anyone here have any suggestions on how I can get connectors for my poles at different angles (15 and 35 degrees, if I remember my dimensions correctly)? Thanks.

The Quest ones are 145 degrees, or 35 degrees from straight, which is what I think you mean.
If you are willing and able to install the elbows on the tent, rather than on the poles, Ti tent pegs can be carefully bent with a large radius to wider angles. The 3/16" Ti peg material will hold the bend, the smaller diameter ones - not so much. You can even use good quality ALU pegs, if they don't have to be bombproof. However, this approach does not allow all the sections to be shock cord connected, even if the elbows are left on section ends of the poles. But there is some advantage in not cording ALL the sections - less cumbersome.

For cording ALL the sections, you need the hollow, tubular elbows you are probably looking for. Montbell and some other tentmakers have them, because they are on their tents. I have made them out of Adventure 16 tent pole tubes by using a tube, not a rod, bender and heating with a burner.
When they cooled off, they still had enough temper to hold. That older tubing was probably the less tempered grade.

If the Quest (Easton) elbows are heated, they lose their temper and will no longer hold the angle under stress.

You could try a cold bend with a bender on other ALU tube that is not as tempered as the Easton.

You could email roger@backpackinglight.com and he might have some suggestions.
He has been very helpful to me on a number of occasions.

If I think of or spot a lower angle bent tube elbow, will post it here.

Edited by scfhome on 01/18/2012 18:53:22 MST.

Another possibility would be to not use elbows, but instead use a more flexible composite tubing for appoximately the middle third of each hoop pole.

Here is an example of what you get with A16 ALU alloy poles for roughly the outer thirds of the hoop pole, and more flexible Early Winters Omnipotent fiberglass poles (1/4 oz/running foot - same weight range as carbon) for the middle third:



As I recall there were two alloy pole sections at the end of each pole, and three slightly shorter FG sections in the middle. The EW sections are 1/4" thick and fit perfectly into the ferrules of the A16s. The resulting hoop is a little wider at shoulder height than a the usual parabolas, so quite roomy.

You could do the same thing with lighter and stiffer carbon instead of ALU for the outer thirds (roughly). The EW poles were very strong, and a lot more flexible than alloy or carbon, maybe too flexible for the entire hoops of the Omnipotent tent.

Now the engineers among us might say that the transition point from the stiffer carbon to the more flexible FG will be ripe for breakage. But for a hoop tent, you will probably want side guys for high winds, and if you put the guy points at those transition points, butressing the hoops at those points in high winds, that might go a long way toward addressing that concern. That pic was taken well above tree line on Mount Madison in the NH Whites - pretty windy, and no side guys on the poles. How could we legally pitch there? - we did, but that's another story.

You can probably find good quality FG tube at kiting and fishing supply sites; but if not, you can PM me about purchasing a few of the EW poles. I promise not to soak you. (Unlike modern day manufacturers, EW sold the poles separately, as much as you wanted - so I ordered a bunch and still have a few left.)

Coupling the larger O.D. carbon poles to the smaller O.D. FG ones is an issue that also must be addressed. Some hunting, luck and serendipity will usually suffice. More on that by PM if you like.

Dare I say, to me the hybrid pole shape looks nicer than elbows. Easier to thread into the sleeves, also. Hope Roger doesn't see this, though.

Samuel,

Thanks for the suggestions. I'm not sure I would be able to find tent pegs that are big enough to serve as connectors for the carbon poles I have. I'll look into the composite pole idea, though that might require a redesign of the tent panels.

Your thoughts did give me another idea - aluminum tubes can't be cold worked without a loss of strength, but the same wouldn't be true for titanium, if I remember correctly. I might look at bending titanium tubing to the necessary angles.

Hi Aaron

Email me, roger@backpackinglight.com
Check out http://www.bushwalking.org.au/FAQ/DIY_RNCTents.htm as well.

Cheers

Fibraplex also has 145 degree elbows. You might call them and see what else they have. They must have replicated the pole sets for most tents by now.

here

Hi Sam

> Hope Roger doesn't see this, though
:-)

> Easier to thread into the sleeves, also.
I have both straight and with-elbow poles. Can't say I have noticed any real difference in threading, even in bad weather.

In response to others: It IS possible to use aluminium tubing as an external sleeve over the CF tubing, and it has been done. Pictures in the FAQ. Easier to bend maybe.

Cheers

Fibraplex uses aluminum elbows that fit over hollow carbon fiber ferrules that fit inside the carbon fiber poles.

I had one Fibraplex pole break and it broke at the ferrule. Break was due to overflexing of the hooped pole set. Fibraplex fixed it for free and changed the bend of the aluminum elbows to reduce stress where the ferrule broke.

Edited by lyrad1 on 01/22/2012 15:59:27 MST.

Daryl,
If Fibraplex could change the angle on your alloy elbows for carbon poles, they could probably provide Aaron with whatever angle he wants. He might have to buy some poles from them, though. Hope the rumor about them increasing the strength of their poles is correct.
Now I will go to Roger's site and see if there is any new info about making elbows. When I made some 3/16" ones from Titanium tent pegs last year, it was painstaking. Don't try it in a cold room or with a short radius rod bender - snap!

Aaron - Just a quick session with a protractor and some graph paper suggests to me that a 145 degree angle would be AOK for building a tent with Roger's design. Just sketching the three angled pole out on graph paper makes it look like there will be too much spread of the poles toward the tent bottom; but that is OK, because you are going to bring the bottoms tips of the pole together, flexing and arching the whole assembly. That creates tension to keep the floor spread taut, and just right for enough angle to both the upper and lower walls to shed rain and snow, with lots of shoulder space. Am wondering if you are reading 145 degrees to be 45 degrees, or perhaps are not considering that the pole assembly will be flexed.

[Edited to remove application of Quest .340" O.D. elbows that will not work].
There is an application for the Quest .340" O.D. elbows that might work well for you; in that the ferrules on these elbows fit well into the Easton Carbon FX pole sections that one poster PM'd me are now available from poleforyou in smaller than wholesale quantities. The FX weigh a little under 12 grains per running inch, compared to the 8-9 grains of the arrow shaft sized carbon poles. But the FX are quite a bit stronger, and will make your tent sturdier. The only downside would be the long length of the Quest elbows, since they include ferrules at both ends, so would be a little more unwieldy to disassemble and fold up than poles with shorter elbows. The Easton elbows from Quest are really well tempered also, and will hold the angle upon which the tent structure depends.

The Fibraplex elbows are sized for carbon tubes, but if they fit over the tube as stated above, would be too small to fit some larger shafts, Victory 300 for example.
So, for them you would probably have to use the Fibraplex shafts, for which the elbows are made. It would be worth it if you could find some slightly thicker walled shafts the same diameter as the Fibraplex, because additional layers of the wrapped carbon will improve the strength of the poles.

The great thing about tubular elbows, as opposed to solid rod ones, is that you can shock cord the whole pole together, which would be much easier to contend with in Roger's design. The pole set does not fold completely flat, as it would without elbows, but folks have been putting up with that for a long time with elbowed poles on tents. The design I was working with using solid rod Ti elbows was much different - just one elbow connection at each of two tent apexes, and nothing like what you are considering, so maybe my comments about making solid elbows were not apropos.

I'm sure Roger and his site will provide you with lots of help if you are going to make a tent with his design. That improves your chances of success way more than striking off on your own. I have a basement full of failed creations that support that observation.

Edited by scfhome on 01/22/2012 23:31:02 MST.

Roger: thanks for your reply. I'll send you an email when I have some more time to sit down in front of my design. I have spent a number of evenings reading through the wealth of information you have on your site. Excellent stuff.

Daryl: I'll see if I can get in touch with Fibraplex. My only concern is the poles they spec on their website are pretty narrow, so I don't know if they will have anything that is compatible with the larger diameter poles I already have.

As an aside, I don't know why more companies haven't switched to larger diameter, stiff poles in conjunction with bent elbows on tents. With carbon fiber and even aluminum poles, creating a larger diameter, thinner walled tube gives you a much stronger structure for the same weight. The carbon tubes I'm planning on using are noticeably stronger than the DAC or Easton aluminum poles, and are (if I remember correctly) about 1/4 of the weight.

Samuel: When I did my initial design in SketchUp I assumed I would be able to get elbows in whatever angle I wanted and thus designed my pole hoops (and thus the angles between the tubes) to what I though would be an optimal configuration. I might have to reassess that approach. The elbows that Quest has look promising - I'll have to email them to get the full specs to make sure they will fit my poles, which are 0.385 OD/0.346 ID. I'll play around with my design a bit tonight and see what I can come up with.

The lower diameter Easton elbows that Quest sells are made of the .340 O.D. tubing - tempered. The ferrule, or "insert tube" that comes out of each end of the elbow has an outer diameter of .287". Naturally, it fits into pole sections of the Easton .340 tubing; but also, sections of the Easton carbon FX tubing, as mentioned earlier.

Unfortunately, the inserts are bonded into the elbows either by spot welding or some other virtually indestructible process. You can't use heat to remove them, because it will destroy the temper of the elbow, rendering it useless. At an earlier time, Quest's elbows may have used heat release glue - at least that's what the Quest folks thought, but no more. The inside diameter of the ferrule, or insert, snugly takes a 0.21" diameter carbon rod.

The inside diameter of the .340 elbow outer tube is .290". So I suppose that if you have carbon tubing that is below .290", you can cut off the part of the insert that protrudes, and bore it out, being careful not to heat up or damage the .340 elbow tube and thus destroy its temper. Was thinking of boring the insert material out to about .242", so a .240" O.D. pultruded carbon tube or rod could be used to connect a Victory 300 arrow shaft to the elbow. Since only one elbow connection is needed for my purposes, I would probably use a piece of solid carbon rod for the extra strength. It is a tricky business, though, because any point where the elasticity of the joint changes greatly - that is where there will be a break.

Don't know what you have in carbon that is 1/4 the weight of alloy poles like DACS, yet stronger. Forgive me for being skeptical. The Easton carbon FX is over half the weight of DAC-FLs, and is a lot stronger than nearly all lighter arrow shafts. When Easton brought it out, they said it was similar in strength and flexibililty to its .340" alloy tubing.

Quest also sells larger Easton elbows that are .433" O.D. with an inner diameter of .373". The insert for those is .370" O.D. Don't see a match for your carbon tubes, but maybe you can figure out something. Easton's .344 O.D. tubing is not as sturdy as the .340", but if they have elbows made of it, it would fit inside your carbon. A couple years ago, a customer service person for Easton at 801-526-6243 was kind enough to send me some samples of some connectors.
Good luck.

Edited by scfhome on 01/25/2012 00:13:36 MST.

Hi Sam

> Don't know what you have in carbon that is 1/4 the weight of alloy poles like DACS, yet stronger.

The CF arrow shafts I use are similar in strength to the Easton alloy poles, but only half the weight. Not sure about getting as far as one quarter. That would have to be a larger diameter tube with a very thin wall, and there are real problems there.

I do know that my poles are significantly lighter than the Carbon FX.

Cheers

Roger, are the details (source, specs) for the carbon tubing that you use on your website (I haven't had a chance yet to look)? Is this the 5-layer lay-up tubing that you have referred to in the past? I take your expertise seriously and I would be interested in knowing if I can obtain these tubes somewhere for my own tent project.

Roger,
Agree.
Hope you don't mind if I share with Colin my attempts to find your pole material, and eventual choice, with your assistance, of Victory arrow shafts. I believe we concluded that the Victory 400s were closest to what you were using. I am using the 300s, slightly heavier and slightly stiffer, because they break-tested for me with some additional strength, and fit perfectly into Easton .344" tent tubing that is readily available at Quest to use to make external ferrules. They make a nice hoop, about 40" high and about 87" wide at the base, but I would not try to stress them with any radius tighter than that. Victory has several lines of shafts - am talking about the V-Force V6, not the much lighter High Velocity, and not the X-Killer. Don't think there is any reason to spend more money for higher tolerances when it is just for tent poles. I am told they are available on eBay.

Hi Colin

Happy to assist.
I can't give exact specs for the arrow shafts I use because the importer won't cough up any details. But I can sure speculate with some confidence.

To the best of my knowledge, there is ONE machine in China for making this 2D wrap stuff. You can see the machine at http://www.pulwellpultrusions.com/applications.htm Again, as far as I know, all 2D wrap arrows come from this machine.

As far as I can judge, the Victory arrows are essentially the same as the SkyShark and GoldTip arrows, not withstanding their expected protestations. All these tubes have an ID of 0.245", with small variations in OD, thus (using the Vistory web site data purely as an illustration):
VForce 300 - .304"
VForce 350 - .298"
VForce 400 - .295"
VForce 500 - .290"
VForce 600 - .285"
Why 0.245"? My guess is that is 1/4" (0.250") rod precision ground down.

There is a wide range of Easton tubing in very fine steps of ID and OD, so you pick the combo you want. I find an OD of about 0.295" works fine for me. Sam went for something a shade stronger.

I do bend the poles in my tents, but I limit the design radius to 1.8 m. That leaves some leeway for extra bending in a storm.

So, can you buy this stuff? Dead easy, from any of the usual channels. Archery shops, ebay, Amazon, etc.

Elbows: that's harder. I make mine from 1/4" SS tubing, turned down to about 0.240" in a lathe. You do need some clearance! Then having machined the two ends of an elbow, I bend it in a custom bending jig to within about 1 degree. My typical angle would be a 31 degree bend. But you use any bender able to handle 1/4" tubing if you get a bit of practice at reaching the correct angle. Finally, because the shoulder at the end of the machined section is NOT large enough to block the tube from sliding up over the bend and jamming (and breaking), I cover the middle of the bend with heavy heatshrink tubing with an adhesive core. I use too much heatshrink and cut it back to the right position while it is cooling. The result can be seen in the FAQ at
http://www.bushwalking.org.au/FAQ/DIY_RNCTents.htm#Poles

However, while I favour my internal SS elbows, others have used a softer aluminium tube to make an external elbow - for this see
http://www.bushwalking.org.au/FAQ/DIY_RNCSummer.htm#Sven

Two details I will emphasise:
You MUST have strong bungee cord through the pole or the parts WILL fall apart while you are handling them! Especially when threaded into the sleeve.
Pole feet should NOT have knobs on the end, even though many vendors have them. Get mud and grit around that knob and you will have a LOT of trouble extracting the pole foot from the grommet! And the knob is NOT needed to keep the pole foot in the grommet.

It is left as an exercise for the reader to work out why I say these things... :-)

Cheers

Hi Roger,
Thanks for posting in detail.
Here's been a problem:
When the poles are attached to the elbows, they can exert quite a bit of leverage on the elbow. If the elbow is highly tempered, or made of very strong material, like 3/16" O.D. titanium (from tent pegs), it will resist the leverage quite well.
If not, it can bend out of shape, especially when high winds on the canopy are trying to distort the poles at the elbows. And repeated bends = failure.

All of that is more critical where my one elbow per pole design depends on maintaining the elbow angle in order to maintain the integrity and function of the structure - it might be less of a concern where there are three elbows on each pole, as on your designs - don't know.

Since you venture into much more blasphemous weather than I do, it would be interesting to know if you have had any issues involving your shop-made elbows' failing to maintain a constant angle.

Thanks.

P.S. I have been experimenting using kite maker's high quality plastic dihedral fittings to connect carbon rods in a pack frame. They are at an angle of about 30 degrees from 180, or 150 degrees, and have a hole in the center for a third rod to pass through at a right angle to the plane of the 150 degree angle. Although the fittings are stopped to prevent the rods from pushing into the center hole, they could easily be drilled out so that shock cord could pass through.
The size rod/tube they accommodate can go up to as high as 9mm. They might have an application here. One site is:

http://www.goodwinds.com/merch/profile.shtml?index=1057765797_2794&cat=connectors.dihedrals&loc=&listpage=1

The hole in the middle is troubling in terms of the strength of the joint, but necessary for the kite makers. But the fittings are designed to hold the angle. With the larger dihedrals, the strength might be acceptable, and carbon tubes might be adapted to fit. Just a thought.

Edited by scfhome on 01/26/2012 19:34:57 MST.

I think I've got a solution worked out to my problem using the 145 degree elbows that Quest sells. They are designed to work with 0.340/0.344 diameter poles meaning the inserts, that are sized for the proper poles would be too small to fit my poles. However, I confirmed from Quest that the total length of the 'elbow' part (not the inserts) is about 4", meaning there is about 2" between the end of the insert and the bend. Since this part of the elbow is made with the 0.340 OD tubing, it should fit perfectly inside my tubing (0.346 ID) to form an elbow join. I can then cut off the inserts, or bond a small length of 0.340 OD tube to the insert to give me a bit longer connection surface. I can probably even do a bit of cold bending of the elbow to get the exact angles I want. Hopefully this all works out.

Hi Sam

> they can exert quite a bit of leverage on the elbow.
The bending forces on the elbows are the same as on the CF tubing. Actually, that force is not that high in calm conditions, so you should not experience any problems at all. Certainly I have never seen any problems undeer calm conditions.

In a storm there are some extra forces but how that plays out depends very much on whether you allow the tent shape to distort. Allowing significant distortion of the original design is inviting disaster, so I don't. If you do allow the tent to distort significantly there will be problems: elbows could bend and poles could break. The reason I don't get a lot of extra bending is that I make very serious use of guy ropes. The myth of 'free-standing' is a total joke in a storm! If you preserve the design shape of the tent then most of the increase in loading manifests itself as compression of the CF tubes, and they can handle that *just fine*.

Key to a good elbow is the very snug fit between the CF tube and the elbow itself. With a sloppy fit the forces are transmitted over very small areas of CF, which is not good. How many elbows you have is immaterial to the physics.

The difference between tent peg wire and tubing is quite high: increased diameter is everything. That is why one can use commercial Al tube over the outside of the CF tubing as an elbow.

I'm interested in that bit abou the kite fittings. Where does one find the angle of the dihedral? I looked, but could not see. I use 31 degrees right now, but the design culd be adjusted to 30 degrees I think.

Cheers

Roger,

What are your normal tolerances between the elbow and tube diameters to ensure a "sung fit" yet still allow the tubes to separate relatively easily?

Aaron

(sorry for the threadjack but I thought other DIYers might be interested...)

A question for Roger:
I've been looking at making a simple straight carbon pole for my trailstar. Do you think that the wrapped tubing (e.g. the skyshark stuff) with an OD of 0.319" (8.1mm) and ID of 0.244" (6.1mm) is strong enough for a straight pole 48" long to support a trailstar or similar? I'd probably make it in 3 sections with one of the solid carbon ferrules joining the sections.

Also, would larger (and obviously heavier) pulltruded tubes be stronger? For example I could used a 14mm (OD) x 12mm (ID) tube with a 12x10 tube as internal ferrules.

Any advice on how to make a *strong* straight pole for the trailstar would be appreciated.

Cheers,
Stuart