MYOG Tunnel Tent – Pole Connector questions

OK, you guys have sort of convinced me. Hope you're right.
But am not going to buy a machinist's lathe. Can't afford such things.

As Daryl said:

"The challenge, of course, is to then find an internal ferrule strong enough …"

Yes, and one that fits as well.

So be it.

Cheers, I guess.

Hi Sam

Lathes – a little secret. There are lots of them around. Farmers have them, and so do retired men playing model railways, especially the steam freaks. Chase around, with a few cans.

Cheers

Roger,
There are a couple who have a big model railroad shop in Intervale NH, so I will go up there and see what I can find out. Of course, having one and knowing how to use it well are two different things.

Quarter inch diameter 6061 T6 tubing is available in three different wall thicknesses from onlinemetals.com, and could be turned down to just the right O.D. Was thinking of paying a local machinist to do it right. Any thoughts about wall thickness and suitability of 6061 T6 for a strong enough inner ferrule for CF wrapped tube with an inner diameter in the .243-.245" range? Material from onlinemetals might also be suitable for the elbows that Aaron started this thread about, way back when.

BTW, don't think the wrapped arrow tubes are all made on the same mandrel, as the inside diameters do vary a bit. There is a nice little discussion at skyburner.com about their manufacturing process that you may find interesting:
http://www.skyburner.com/skyshark/ssnews.html
Sorry, no photo of the machine, though.

Am thinking about doing some tests of both tubes and ferrules by bowing two 30-32" tubes connected by a ferrule at the center, pushing one end toward the other until failure; and measuring how far apart the ends were at the time of failure. Will just have a tape measure open on the mat as I push. Could try both internal and external ferrules of different materials and lengths, and try with Victory V6 300s, SkyShark P400s, and Fibraplex, a nice range to work with. Goggles and gloves, on … push!

Could stuff pole tips in the tube ends just to hold onto for the tests. Or I could install a small fish weighing scale at the pole tip and pull on it to also register the pounds of force at the time of break, but that would make the process more difficult. Photos of the breaks would also be interesting, especially if at the ferrules, as I expect. What do you think?

P.S. "Chase around with a few cans" You lost me with the cans. Are you meaning to suggest that I get married?

Hi Sam

OK, first off, what SkyShark call a wrapped tube is a bit of CF fabric wrapped around a mandrel – like the Fibraplex ones. That is very different from the '2D wrap' construction I use.. Yes, they make quite a few IDs in wrapped-fabric tubes – low capex.

> P.S. "Chase around with a few cans" You lost me with the cans.
Australianism? Cans of beer!

Aluminium tubes:
I know the 6061 can be bent with a proper bender. Not sure about the 2024 – that alloy you would need to test (and it's all too big anyhow). 6063 is definitely softer – I would prefer the 6061.
0.25" OD x 0.035" WALL x 0.18" ID – ooh, thin wall!
0.25" OD x 0.049" WALL x 0.152" ID – hum …
0.25" OD x 0.058" WALL x 0.134" ID – possible
0.25" OD x 0.065" WALL x 0.12" ID – yeah, possible

They also do some nice SS tubing. Their prices are … not cheap, although you don't need a lot.

> doing some tests of both tubes and ferrules by bowing two 30-32" tubes
Fun stuff. I did a lot of stiffness testing, but staying in the linear range!
Oh, I can see lots of fun with goggles and ear plugs. Yes, real live test data!!!!
(Use a small empty room for testing: the middle bits can go flying!)

Cheers

Hi Roger,
Not sure of your terms, but yes, I have noted your descriptions of the manufacture of multi-layer wrapped tubes on other threads, and see the clear difference. Did order a couple of SkyShark 400s for testing, though. Initially, will just use my old method of sticking it into a metal tube in a brick wall, attaching a hang scale to a connecter on the end of the CF tube at a precise distance from the brick wall, and pulling slowly until the break. But only if I can find a tube to go into the wall that will fit snugly over the P400 – expect so.

If it becomes necessary to turn down the 6061 T6, will use the thickest .065" wall as you suggest. Some must come off to get down to around .243" O.D. Goodwinds has an aluminum ferrule that is spec'd at .243" O.D., but is actually around .248". What a revoltin' development. After my most recent talk with them, I think they may change the spec listed on their site.

Will look into the SS tubing if the 6061 T6 bends in use.

Re: Ear plugs. Have broken quite a few, including the Easton FX, and no big bangs so far. But the shock totally discombobolates the 50 lb. fish hanging scale, and often the pointer and cover plate come flying off, so the scale must be reassembled and recalibrated after each test. Good suggestion about the empty room – wish I had one.
But it is the basement workshop, and is a total mess already. Squalor. Very unscientific. Some of the gear made there has been good, though. (And some – not so good).

Hi Sam

Another way of applying force without too much disaster. Bucket 2" above ground. Slowly add water, 1 L at a time. 1 L = 1 kg.
If you use a wide bucket, it is unlikely to tip when it falls. Bit of a splash maybe, but you were counting the number of 1 L additions … Outside.

Cheers

Hi Roger and Daryl,

Well, I now have two machine shop estimates for 8 6061 T6 ALU ferrules, with two different wall thicknesses, O.D. .244" to fit in a Victory VForce V6 300 carbon tube: $65 and $100. An that's with me supplying the metal.

Found a used Taig metal working micro lathe with all kinds of accessories for $300.

To paraphrase Laurel and Hardy – Now look at the pickle you've got me into!

Life was so much easier with the external ferrules cut from Easton .344 tent pole tube at less than 50 cents each.

Sure hope internal ferrules are really better.

P.S. Not going to even hint at what to do with that bucket.

Found this thread last night as I was investigating possibilities for poles and angle connectors for making just such a tent (Roger, I think I emailed you some tent questions a year or more ago). I'm intrigued by the idea of using the arrow shafts, but not being a machinist am a bit confused by exactly how this would work. I get from this thread that the angles Roger uses are SS that fit inside the shaft, and that the best reinforcement for the ends of the shafts would be internal ferrules at least 1.2" long. But I am not certain about ferrules vs. connectors; do both ends of each shaft have internal ferrules, then the SS angles fit inside those, and the straight connectors fit outside the ends of the shaft? Or do the SS angles take the place of the ferrule where they occur? Or something else entirely? Please clarify (aka Poles for Dummies, said dummy being myself).

I have a colleague (in my orchestra) who is also a machinist; sent him a little about the elbows last night before I found this thread and he may be interested in helping me. I find the sewing end of tent-making far less intimidating, since I have plenty of experience with sewing. But the pole setup is not so straightforward for me.

Thanks,
Debbie

Hi Debbie

OK, lets start with a photo of my tent poles.

In this photo you can see a stack of carbon fibre poles folded up. Details:

The long green sleeves over the CF are Easton arrow shafting used as straight connectors – needed to get the section length down to fit in my pack.

The short green sections are the same arrow shaft used as reinforcing for the ends of the CF tubing. They won't really reinforce the CF tubing againmst splitting – the CF is stronger, but they do protect against bumps, abrasion, wear etc. For the tiny incremental increase in weight, I think they are justified.

The shiny things are the SS elbows which go inside the CF tubing. They are bent at about 30 degrees, and they have a short bit of heavy heat shrink tubing in the middle of the bend. The heat shrink stops the ferrule from penetrating in too far and jamming at the start of the bend. So each elbow really has two shiny ends and a black bit in the middle.

The elbows started life as 1/4" SS tube, cut to the required section length. Then I turned each end of the bit down to a really snug fit in the CF tube. This left a larger diameter region in the middle – under the heat shrink.

How are we going?

Cheers

Hi Sam

> two machine shop estimates for 8 6061 T6 ALU ferrules … $65 and $100… with me
> supplying the metal.
Sounds fairly cheap as a commercial thing.
That's $10 for the machining, $50 for the set-up, and the rest for time talking to the customer.
Yes, seriously.

Ah, but with your own lathe … welcome to the slippery slope into a complete machine shop. (Drill press, manual lathe, manual mill, CNC machining centre …, CAD, …)

Cheers

"How are we going?"

OK, this helps. I understand the elbows. Also the long green connectors (one per joint excepting the joints that have elbows in them, yes?).

I can't see well enough on my screen for much detail on the short reinforcing pieces at the ends, but I think I get the idea.

Four questions remaining (unless the answers spark even more questions):

1) Do *all* shaft ends have internal ferrules? (those that fit into straight connectors, those that fit into elbows, and those that hit the ground?)

2) Are the short green reinforcing pieces only at the very tips of your poles, i.e. the end that hits the ground? If not, then I'm confused about how they would fit in with the elbows and straight connectors, so I'm hoping I'm right there.

3) What are your internal SS ferrules made from (tubing outer, inner dimensions?)?

4) Are the ferrules, connectors, elbows epoxied onto a shaft or do they just fit really snugly?

Many thanks.

Hi Roger,

"The long green sleeves over the CF are Easton arrow shafting used as straight connectors – needed to get the section length down to fit in my pack."

What! External ferrules? Seriously, I already knew you use external ferrules; so was a bit puzzled by your earlier post. But figured you had moved on. Maybe not.
Your point is still taken, however, as the elbows, inserted inside the carbon tube with the shorty outside collars, appear to be where the stress will be focused 'when things go wrong,' hah-hah. Nice work with your pole set!

Yes, am now the proud owner of a nifty little Taig metal working lathe, with lots of nifty accessories. Got some 6061 T6 quarter inch tubes, but the I.D. is tiny. Not much room for shock cord. Thinking about turning down the .248" O.D. ALU ferrules from Goodwinds to the .244" needed. Will first need to find their true I.D., then from that the wall thickness, then see how they behave on the lathe, and how much strength remains after losing .002" of wall.

Then come the break tests as earlier described. Data, Roger! Just imagine.

Am cheerfully slipping down the slope. Everyone else is out skiing on groomed corn snow.

Sorry about the resolution – the Forum SW shrank the pic. So let's try agan.

1) No. Elbows are internal, straight connections are external.

2) The short green rings are only at the ends of the CF sections.

3) The internal ferrules are 1/4" stainless steel tubing turned down in a lathe to be a snug fit inside the CF tubing.

4) The external green straight ferrules and reinforcing rings are epoxied in place.

There is bungee cord inside the poles – actually a short length of bungee plus a long length of string. It was lighter that way.

Cheers

Regarding #1: So the only internal ferrules used are the elbows?
#2: Reinforcing rings only where elbows connect and at "ground" end, yes? Otherwise I can't figure how the straight connectors would go over them.

At least I'm having fewer questions each time…

Roger,

Thanks for all the good info. I'm loving this

The nugget for me in this post was:

"The heat shrink stops the ferrule from penetrating in too far and jamming at the start of the bend."

I've struggled with a similar problem with my pack frame. I like the shrink tubing idea. I've never used shrink tubing but will start educating myself and experimenting.

Daryl

> #1: So the only internal ferrules used are the elbows?
Correct.

> #2: Reinforcing rings only where elbows connect and at "ground" end,
Yes

> fewer questions each time…
Good!

Cheers

Hi Daryl

Yes, but I use a heavy-wall tubing with a hot-melt adhesive inside, and the ends of the heatshrink do go past the shoulders on the SS tubing. That way the heatshrink locks on a bit better.

Digs through old notes …

Samples tested included:

Canusa Brand
CPA 100 95 ID 9.5 mm -> 3.4 mm, 1.3 mm wall 8.3 mm OD over SS
CPA 100 64 ID 6.4 mm -> 2.0 mm, 1.3 mm wall 7.7 mm OD over SS

Tyco
ATUM-9/3 ID 9 mm -> 3 mm, ? wall 7.8 mm over SS
SCL-3/8 ID ? mm -> ? mm, ? wall 8.0 mm over SS, USED on several tents very nicely

Raychem
? ID ~20 mm -> 7 mm 9.2 mm OD, (100 mm length)

Cheers

Thanks, Roger, for all the details – and especially for your patience with my questions!

Debbie asked me:
" what is the green aluminum arrow (model/size) that you used for the straight connectors"

That does depend very much on what CF arrow shaft you are using. You need a snug fit.

To explain: Easton make aluminium arrow shafts in a huge range of sizes. They have a wierd code number system which make perfect sense once you understand them. For instance:
2117: this means the OD is (about) 21/64" and the wall thickness is (about) 0.017"
2219: OD 22/64", wall 0.019"

I use 2117 over my CF tubing, but I don't know what CF tubing you will buy.

Cheers

Aha…good to know. I'm considering (if my machinist friend agrees to do the SS tubing) either the Vforce V6 400's, which it sounds like you used something similar to, or the 300's. So knowing the system for the aluminum sizing is very helpful.

From what you said earlier in the post, it sounds like you used an aluminum shaft with an inner radius 30-50 microns (larger) than the CF (external) radius. So I may need to either visit an arrow shop with a micrometer, or get hold of a few sample shafts to have my friend measure to find a good pairing.

Thanks yet again.

Hi Debbie

> I may need to either visit an arrow shop with a micrometer, or get hold of a few sample
> shafts to have my friend measure to find a good pairing.
Yeah, I reckon first buy the CF shafts, then measure them, then buy the aluminium. Nothing beats actually fitting the CF tubes into a physical arrow.

Cheers

Hi, Roger – I'm wondering how long the main sections of your poles are (ground to outer elbow, outer elbow to center elbow) and how many pieces in each of those sections. I'm trying to figure out how long I'd want to make the sections; obviously fewer sections would require less hardware, thus be lighter, but I'm wondering if that would end up being weaker. If you break each section up into 2 or 3 pieces, is it best to make them of equal lengths? Is there an optimal length for the CF sections in terms of strength and/or flexibility?

Sitting on the ground, my head tops off at 37", so allowing for a pad, hat, and fabric sag, I probably want at least 42" height in the tent. So I could conceivably use either two 21-22" or more likely three 14-15" sections for each "side", then probably four across the "top" (~14" each). Is that the best way to go about it?

Debbie

Hi Debbie

> how long the main sections of your poles are
Go to Part 1 of the Tunnel Tent Survey and Tutorial and look at the photos of the blue tent under Elbows and Tension.
I have 2 sections from ground to the corner, and 1 section from the corner to the peak, on each side.

There were two constraints which dictated this division:
Fitting the sections inside my pack: I do not have gear on the outside
Length of available arrow shafts

> Is there an optimal length for the CF sections in terms of strength and/or flexibility?
Not really. I limit the curvature of the CF poles to a safe amount, that's all.

> so allowing for a pad, hat, and fabric sag
Pad, yes, but I don't wear my bush hat in the tent, and there is very little fabric sag in the fly! OK, a little (not much) in the inner tent for winter.
While I think it is OK to let the height of the summer tent go up a bit for comfort, I keep the winter tent as low as possible – for wind-resistance.

Cheers

An update for 2017:

The wrapped-fabric CF tubes have got better over the years. They are being wound a bit tighter. They are still not as strong as the 2D wound tubes, but they might do these days.

Avoid anything pultruded, Carbon Express (pultruded glass with a dusting of carbon powder over the outside), mistreating the ends of the CF tubes.

Cheers