MYOG Tunnel Tent – Pole Connector questions

[Roger Caffin]

Hi Sam

> the tube broke almost as soon as it started to bend.
Chuckle! You can't 'bend' Easton tubing with a conventional tube bender. You have to roll it in small increments.

I have managed to curve 340 or 344 tubing to have a radius of under 6" with little loss of strength, but you need complex rolling gear.

I was fascinated by your suggestion about composite elbows. Yeah, could work. As a matter of fact, I think you could start with larger 6060 Al tubing which will bend in a bender, and then sleeve that down with Easton tubing. Hum …

Cheers

[Stuart Allie]

Aaron, thanks for that. I agree with what you said – I just can't find any (non-pultruded :) carbon tubing that has a large diameter but fairly thin wall and is available in small quantities. I'll keep looking though.

Roger, I don't know about the Main Range but the shelf camp at Mt Anne in Tassie can get pretty windy (as I'm sure you know!) so I am looking at something *quite* strong…

Taking your advice and ignoring pultruded tubing… how about the 0.319" wrapped tube with a core of 0.240" solid pultruded rod? Basically using the solid rod as internal ferrules with no gaps so I'd end up with an almost solid carbon pole, pultruded on the inside and wrapped tubing on the outside. That'd still be fairly light (somewhere around 100g I think) and pretty strong I think?

I wlll keep looking for some larger wrapped tubing though.

Thanks.

(P.S. the crux pack is wonderful so thanks for that too!)

[Sam Farrington]

Roger,

Chuckle all you want – the devil made me do it.
After the .344 was warmed up to just above room temp, it actually did bend to about 5-10 degrees, but then still snapped.

Still wonder if a machinist knowledgeable of metalurgy would know how to hot bend the Easton tempered tubing without losing the temper.

Thought about using something akin to your 'rolling jenny,' but decided that an elbow with a 5-6" radius would be quite a bit longer than Aaron would like.

Don't know what those kite dihedrals are made of, but will find out soon enough how strong they are when the order arrives. Need them for a pack frame, as noted before.
The approx. 30 degree angle won't work for the XX tent I'm making. Easton .344s bent to the required 120 degrees would be awesomely better for the tent than the heavier 3/16" Titanium rod cut from tent stakes that I'm using.

About the ALU tubing. Yes – great idea. Saw some 7/16" (11.1mm) 6060T6 tubing on a kite site and ordered a piece. Yes, it will bend nicely with a bender, and probably hold the angle in your application. But don't have a 7/16" bender, so will have to try it with a half inch one, maybe with something to tighten up the fit on the rollers. If that works, will try drilling out the ends of the elbow to fit snugly over the .385" O.D. carbon that Aaron is using. That would produce a fairly light and short elbow that would fit over the tubing, thereby reducing, IMO, the likelihood of failure of the carbon. Stay tuned – there is light at the end of the tunnel (no connection intended with the shape of your tent).

[Troy Ammons]

I dont know if its been mentioned but if you are going to bend aluminum tubing try filling with sand.

I bent some NANOLITE tent poles from Quest by hand into a very tight curve.
Way tighter than straight tubing would allow. Pretty easy really.

It also helps if you are trying to bend tube on a tubing bender. Supports the tubing and helps it hold its round section profile. Sort of like a cheap mandrel.

[Roger Caffin]

Hi Sam

> Still wonder if a machinist knowledgeable of metalurgy would know how to hot bend the
> Easton tempered tubing without losing the temper.
To the best of my knowledge, that is simply not possible. It loses its T9 temper not very far above boiling point, or something like that. Note that T9 is actually off the conventional tempering scale: Easton are the only company in the world to be able to do it.

> Saw some 7/16" (11.1mm) 6060T6 tubing on a kite site and ordered a piece.
Plenty strong enough. Go for it, and let's see photos.

> 30 degrees won't work for the XX tent I'm making. Easton .344s bent to the required
> 120 degrees
I had that problem too, which is why I went from 1 elbow to 3. In *addition*, 3 elbows gave me much better headroom inside. 2 elbows is OK for head room but leaves a flat top which is dangerous for snow loading.

Cheers

[Aaron Robson]

What Troy said is definitely worth a shot – I've seen that technique discussed in a number of different places. Of course, you have to seal the ends of the tube you are bending so the sand doesn't just get pushed out, but it is supposed to give very good results.

Aaron

[Daryl and Daryl]

Aaron,

I don't have a solution that specifically addresses your question. I do have some of the same (or very similar) carbon fiber tubing that you are using, however. Here are a couple of ideas that I offer as food for thought. They may trigger some better ideas from some of the other members.

Here's a post that shows how I used these poles for the fly shown in my avatar.

here

And here's an external elbow I just bent that fits the tubing. I used some scrap aluminum tubing that is OD about .5 and ID about .4. The fitting weighs .5 ounces. It was easy to bend with my tube bender.

Daryl

[Sam Farrington]

Troy,
OK, the Nanolites are the Easton .344s, on the Quest website.

Wondering what 'very tight' is before I go snapping more tubing.
Suspect you must have bent it over a cylindrical form. Wondering what diameter or radius you used for the form. (Was thinking of a tire for some high radius bends I need to make for a pack frame.)

The Quest elbows have a 2.5" radius for a 90 degree bend. Anywhere near that tight?

Would appreciate your advice on these points.
Thanks.

[Sam Farrington]

Daryl,
Scroll back a few posts and read Roger's comment about loose fitting connectors and carbon.

A couple years ago, I did a slew of break tests on every wrapped carbon tube I could get my hands on. Bet you can't name one that I left out. While I was very careful to put the same pressure on each sample, and the results were good enough to steer me to the right carbon tubes (see Roger's post on that above, also), the results were not reliable from a scientific point of view.

The reason? The closeness of the fit of the connector over the carbon tube had to be exactly the same, or the results would vary substantially, even for the very same tubing. The snugger the fit, the higher the break point (pounds of force required to break) – much higher.

At one point I thought I had found the miracle tube, until I realized it was just because I was using a much tighter connector tube over the test piece. It was not possible to address this problem fully, because i did not have connector tubes to fit every piece of carbon tube with exactly the same amount of snugness. But finally got the tests uniform enough to determine that the Victory 300s were 20-30% stronger than most other carbon wraps, like the Sky Shark, and gave the best strength for weight. A lot cheaper too, BTW.

Using a .4" I.D. connector over a .385" O.D. tube would be pretty loosy goosy. Much more likely to break under stress than with a snug fit. It helps to have tube and connector materials with the same flex ('modulus of elasticity'), and to use external connectors that go over the ends of the carbon tube and protect them; but the loose fit is a killer.

Fortuitously, about the same time I found the Victory 300s, I also found that the Easton nanotubes, or .344s, fit over them with just the right amount of snugness – no detectable wobble, but no difficulty with insertion. It is necessary to make sure the connections are clean of dirt and sand before connecting, but that is true of any tent pole; and as with most BPL stuff, the little bit of extra care is the price we pay for the ultra light gear.

[Sam Farrington]

Roger,

No sooner was the 7/16" tubing ordered, than the kite company put a message on its machine that orders will be delayed due to an illness in the family. So it may be a while before there is anything to post. Ordered some custom drilled hubs from the same outfit before Christmas, and they are still outstanding, so now will have to drill one out myself from some hub blanks I got way back from Fibraplex. Have only two to work with, so only one mistake allowed. What fun.

Got some 6mm excel dihedrals from Goodwinds, though. Molded plastic, but very sturdy, with plenty of room to drill out for .24" (6.1mm) carbon rod for the pack frame. They weigh .23 oz (6.5gm), though, a little heavy, but only need to use two of them. Probably too heavy for tent pole use, but just FYI, each end takes 2.5cm of tube/rod. The 8mm ones, large enough to drill out for .295" tube would be even heavier.

Cheers.

[Stuart Murphy]

Polesforyou.com will bend Easton tubing bought from them up to and including 13mm diameter.

The poles are pretty reasonably priced… don't know why you'd want to muck around with it as DIY.

Woops, sorry, just realised you're talking about bending aluminium for use as elbow connectors… please disregard post

[Roger Caffin]

Hi Sam

You ought to be able to buy suitable tubing from many places. Try Mcmaster Carr for instance.
(Sulk- they won't export to me. Export regs are now so complex they don't make a profit any more on export orders becasue of the paper work. That's the USA Govt helping American industry.)

Snug fits – YEAH!
However, if you get some snug-fitting Easton arrow shaft which fits over the CF tube, you can epoxy a short length over the end of the CF tube to *help* reinforce it. It might help prevent what you can see below. (I had better add, that pole was not on MY tent! The damage was due to misuse.)

Cheers

[James Marco]

One trick I picked up from building fly rods was to wrap the connection with fine thread. Then use heated (gently heated) epoxy over the threads to hold tension. This adds a bit of pre-load from the tight thread wrap. It will add a gram or two of weight but also adds a LOT of reinforcement to the ends of the poles. About 3-3.5 times the diameter of the tube, down is a good compromise between strength and weight for the connector. I believe they use similar techniques to make barrels by heating a band, pressing to quickly over the wood and letting it shrink.

Looking at Rogers pic, the connector is really too short. The ends should also be sanded smooth as in the pic. You can see the miltiple layers of delamination. Thread wrapping helps prevent that. Epoxy makes it smooth for easy insertion into whatever.

[Daryl and Daryl]

Samuel,

Thanks for the info. I had noticed the snugness comment from Roger and your experience really amplifies the importance of it.

I'll keep the Victory 300s in mind for future projects. Been using Skysharks. There have been some good deals on Skysharks lately. That's how I ended up with the .385" od stuff.

My primary aim in making the elbow was to see how difficult it would be to make one for .385" od tubing. I concluded that it was easy. One just needs to get the right size of tubing and make sure it can be bent.

Back to the snugness factor. I wonder if snugness can be fine tuned by wrapping the carbon fiber tubing with something like foil or teflon tape?

The .385" od carbon fiber tubing also fits into the black nylon 1/2" od barbed plumbing fittings I bought from McMaster-Carr. It only goes in about 1/2", however, so I couldn't see an application to this thread.

Daryl

[Roger Caffin]

> Looking at Rogers pic, the connector is really too short.
Well, that depends very much on the quality of the fit. My own experience is that with a snug fit that length of connector is just fine and has lasted for maybe 8 years of heavy use with zero damage (on my tents).

The connector in the photo was broken by gross violence at the bend by someone else. I really don't think one should infer anything about the connector length from that case.

Cheers

[Daryl and Daryl]

Samuel,

Are these the Victory 300s you referred to?

here

Daryl

[Roger Caffin]

The ones I recommend are the VForce 300:
http://www.victoryarchery.com/carbon-arrows/hunting/vforce/

The 0.245" ID is the key factor.

Cheers

[Daryl and Daryl]

Roger,

Thanks for the Victory 300 link.

I see that they have slightly thicker walls and are slightly heavier than the Skyshark 400s. This might partially explain the better performance in Samuel's strength testing.

Daryl

[Sam Farrington]

Daryl,
No. The ones I've been using are the V6's. On the Eagle website, I think they are these:

http://shop.eaglearchery.com/browse.cfm/victory-v-force-v6-series-shafts-300/4,11271.html

It's odd that Eagle Archery has so many more types of Victory arrow shafts than appear on Victory's own website.

The ones I use are just a tad too large inside to use .240" pultruded carbon tubing as internal ferrules. But a 3" section of Easton .344" "nano"tube weighs no more than 4" of the .240" pultruded carbon, and is a stronger ferrule that also protects the ends of the carbon tube from separating under stress, IMO.

Yes, I also found some plastic hose T's that fit well over the .385", but as you note, T's aren't elbows.

Have not given up totally on bending the Easton .344. Will have to try the sand, but I imagine Roger is right about the futility of it. 7/16" 6060T6 ALU tubing is more probably the answer.

[Sam Farrington]

Roger,
Carbon Express makes a product called "Bull Dog Nock Collars," just small alloy bushings that go tightly over the end of the carbon tube where the nock is inserted.

The I.D. of them is not large enough for the Victory V6 300s, but since the Carbon Express Maxima is the same tubing as a new SkyShark product introduced last year, I thought I would mention it. This tube is identified in part by the carbon weave pattern on the outside that is really just a thin plastic cover – further confirmation of your opinion about Carbon Express – wasting pretty pics on plastic where another layer or two of wrapped carbon would make the tube much stronger.

Folks using internal ferrules on the SkyShark or other carbon tubing of the same O.D., might do well do look into the nock collars.

However, where the V6's will go over a Ti internal elbow, I will also add a short external collar cut from the Easton .344" tubing. It should probably be no more than half as long as the length of Ti elbow that goes into the insert in the carbon tube, the thought being to spread the force a bit when a typhoon hits. The inserts are plastic from Goodwinds that are bored out to a nice press fit over the 3/16" O.D. Ti elbows, and then glued into the V6 tubing with urethane glue – nothing fancy like Hysol, just Elmer's or LePage's. It expands as it dries, making it great for holding inserts and outserts. I had trouble with the hardeners in some epoxy glues weakening the bonding agent that holds carbon fibers together, so stopped using epoxy.

Sorry to hear of your difficulty with shipping from McMaster-Carr. I've been having trouble bringing up pages on their site lately. They do have a lot of stuff that is hard to find, and at lesser prices than some others.

[Roger Caffin]

Hi Sam

The best I could do was a 4" radius. Even with a proper rolling jenny, the tube was starting to flatten at that point. A 6" radius would be a wise limit.

> It's odd that Eagle Archery has so many more types of Victory arrow shafts than appear
> on Victory's own website.
A lot of the shafts are a bit 'hidden' on the Victory web site. You have to burrow right into the pages and roll down a bit.

Cheers

[Daryl and Daryl]

I've posted this before but it fits the current discussion so here it is again.

A kitebuilder forum member did some destructive testing of spars here:

here

This is a test of spars, not ferrules.

He concluded, among other things:

(1) That a ferrule length of 4 times the diameter of the spar was adequate, with little strength being added after that.

(2) That internal ferrules resulted in a higher breaking strength than external ferrules for the Skyshark 400s. The challenge, of course, is to then find an internal ferrule strong enough to match the Skyshark 400 shaft strength.

(3) That wrapping the spar tip with string, tape or a tubing piece (as suggested by Samuel) would reduce shaft failure from an internal spar.

Seems like the first thing to determine is where the weak point is. Wrapping the ends of my Skyshark 400s, for example, wouldn't help if the weak point is the ferrule. When my Fibraplex pole broke, for example, it was at the ferrule.

[Sam Farrington]

Congrats Daryl, you win my bet. As best I can determine, the SkySharks I break-tested were the P300 and the P3X, both of which were no better than average. The P400 you mention, I did not test, probably because it was not on Goodwind's or Kitebuilder's site at the time. I see that it is a thicker walled tube, weighing around 8.97 gsi, or .58 gm/in, compared to the 8.2 gsi, or .53 gm/in, for the P300. So, it might well be above the average strength for the tubes I tested. The P3X are no longer listed on the Goodwinds site, because they quickly sold out of them and did not restock; however, IMO they are the same tube as the Carbon Express Maxima shafts that are readily available (They appear the same, have the same O.D, and weigh the same to a thousandth of an ounce). By comparison to the P400s, the Victory V-Force V6 300s are around 9.8 gsi, due to even more thickly walled tubing.

I cannot concur with the conclusions from the post by the kitebuilder forum member you linked to. Specifically:

1. I don't think he was referring to ferrule length as being 4 times the shaft diameter, but to the length of insertion or "engagement" of the ferrules into each tube. Carbon arrow shafts generally run below .3" O.D. Four times that is 1.2". A 1.2" ferrule would be woefully short, and would not distribute the stress of a bend over a wide enough arc, an invitation to breakage. Both Fibraplex and its predecessors have used 4" tubes for internal ferrules for carbon poles. Makers of alloy poles, like Easton and DAC, typically use 3" ferrules.

There must be some amount of looseness between the main tube and the ferrule; otherwise the tube could not readily slip into or over the ferrule. Even when that looseness is minimized, there will be some slight amount of cant between the tube and the ferrule, resulting in more pressure on the main tube at its lip, and at the point where it passes over or out of the lip or end of the ferrule. The longer the ferrule, the more this pressure is distributed when the entire pole is flexed, I believe.

The kite forum tests seem to contradict this; however, as I discovered, the degree of snugness between the ferrule and the main tube markedly effects the resistance to breakage, and differences here will totally skew break test results. I did not see anything in the kitebuilder forum test methodology to assure equal snugness, the same mistake I made when I began break testing, and the reason why I have not published my earlier results.

2. What I would like to see in support of the kite forum test conclusion about internal vs external ferrules is some reason to believe that internal ferrules are more reliable than external ones. Without that, I would not accept the kite forum test results without evidence of some control for snugness. Morevoer, an external ferrule offers more of the same protection from breakage that a collar over a carbon tube does, a proposition you accept. Even with the transverse wraps, carbon poles are prone to damage or separation at their ends, and the external ferrules also prevent that when in place. Internal ferrules do not.

However, I can see how internal ferrules of equal snugness might arguably be less likely to break a stressed tube than external ferrules would. With an external ferrule, all other factors being equal, when the pole is arced and stressed, more of its surface is exposed and forced against the lip of the ferrule than is the case with an internal ferrule. Indeed, this may have something to do with the reason why Easton chose internal alloy ferrules for its carbon FX tube poles. But even if the kitebilder forum tests are correct about internal ferrules being less likely to occasion breaks in the main tube, there remain some practical considerations.

3. .240" O.D. pultruded carbon tube should be as strong as the SkyShark 400s, and is available at many of the kite sites. The ends can be reinforced by soaking with Cyanocrylic glue (Krazy glue) – best I've found for this purpose is Bondini – but since the ends of internal ferrules are protected and reinforced by the outer tube, that helps to protect against wear and tear. Nevertheless, during the period of over ten years I used internal carbon ferrules on carbon poles, I had problems with pultruded ferrules eventually splitting. This could be corrected before breakage by keeping an eye on them, but was still a problem. But the more serious problem was that the ferrules were either too loose or too strong, causing the main tube to break. Carrying an extra pole section always sufficed, and the alloy sleeves in the pole repair kit never had to be used, but still …

If you break a stick over your knee, it will break where it contacts your knee. Similarly, if a ferrule is stronger and has less flex than the main tube, the tube will break at the lip of the ferrule. So you don't want it to be stonger, or have a higher "modulus of elasticity," than the main tube.

Another more practical problem with the .240" tubing is that most of the carbon tubes used for arrows are manufactured on spindles of the same diameter, and therefore have an I.D. of around .245". Hence, the difference in diameters is .005", compared to the difference of .002" found between poles and ferrules on Easton tent pole tubing. Again, this much difference will markedly increase the likelihood of the main tube breaking at the lip or end of the ferrule.

I could not find carbon tubing of any kind with around a .243" O.D., and that is yet another reason I went to external ferrules, because the Easton .344" tubing fits over the Victory V6 300s as precisely as could be hoped without being too snug. I believe Roger also found Easton tubing that fit snugly over the carbon shafts that he uses.

If internal ferrules are inherently less likely to occasion breakage, it would make sense to use them, but only if a snug fit could be obtained between the ferrule and tube from materials available to MYOGers, and if outer collars were also used. But, so far I have not found materials that would provide such a snug fit, with close to the same elasticity. I did find a fiberglass tube that fit well as an internal ferrule, but it was so elastic, it bent at the spaces between the main tubes. I also found an alloy internal ferrule that fit well, but was only 2" long, not long enough IMO, as I'm not ready to discard the conclusions of the large pole manufacturers in favor of the kitebuilder poster's tests.

So it would be interesting to hear what Roger and others have to say about the argument for internal ferrules; but without availability of the right materials, the argument may have to remain academic.

4. When you state that your Fibraplex pole broke at the ferrule, I'm not sure if you mean the ferrule broke, or the main tube broke at the lip of the ferrule. Frankly, it could be either, because the ferrules Fibraplex was using, at least a few years ago, were much thinner walled than .240" pultruded carbon tube. I then spoke to Linus, and encouraged him to obtain stronger ferrules. With the pultruded tube as a ferrule, a break would probably occur where the tube passes over the lip or end of the ferrule, as noted above. Achieving exactly the same modulus of elasticity for both the ferrule and main tube, while possible for a large manufacturer, may be like looking for Godot for a MYOGer.

I admit that I don't know if the .344" O.D. Easton alloy tubing and the Victory V6 300s have the same modulus of elasticity; however, I did note in my break tests that they both broke at about the same pounds of force, while protruding from external ferrules of as close to equal snugness as possible. So I am optimistic, but accept that as a MYOGer, I can't expect to achieve precise scientific data on this without the benefit of laboratory facilities, and even if I could, where would I get the precise fitting materials with almost precisely equal elasticity.

That's my opinion, FWIW.

[Roger Caffin]

Hi Sam

OK, comments.

> Carbon arrow shafts generally run below .3" O.D. Four times that is 1.2". A 1.2" ferrule
> would be woefully short, and would not distribute the stress of a bend over a wide enough
> arc, an invitation to breakage.
However, my internal ferrules are about that size – 1.2" long.
They work for me because I machine the SS tubing myself so it is a very good snug fit. When the fit is that close, a bit of force causes enough deflection of the CF tubing (or rather the plastic/epoxy used to matrix the fibres) that the area taking the load becomes large. For a more sloppy fit you would indeed need a longer engagement.

> some reason to believe that internal ferrules are more reliable than external ones.
Yes, definitely.
An external ferrule exerts compression on the tube from the outside, and almost all the force is taken by the plastic matrix. The wrapping fibres are in compression, and have very little strength like that. (Long ferrules needed.)
An internal ferrule forces expansion on the wrapping carbon fibres, and they just don't stretch that much! The amount of plastic around them is so small that the fibres are pretty close to touching, so the strength of the plastic is secondary.

> .240" O.D. pultruded carbon tube should be as strong as the SkyShark 400s,
I'll repeat what I said before: pultruded tubing splits catastrophically.

> If you break a stick over your knee, it will break where it contacts your knee.
Yes, if broken over your knee.
However, if broken by bending it will very often make two closely adjacent breaks. Pretty wierd when you see it for the first time, but the two simultaneous breaks are predicted by theory.

Cheers
PS: you need a lathe as well as a sewing machine … :-)

[Daryl and Daryl]

Samuel,

"I don't think he was referring to ferrule length as being 4 times the shaft diameter, but to the length of insertion or "engagement" of the ferrules into each tube."

I agree.

Daryl

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