Making some tall tent poles

[Moondog55]

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Well I thought I'd already done this in my thread about the big tipi, seems 5 or 6 posts have got lost.
Anyhooo. I need to save some weight as even I think 9 kilos is a little on the heavy side. The centre pole that comes with the tipi is steel and really the heaviest single component. I have a set of aluminium poles in the shed that came from an old backyard gazebo sunshade thingie. 25mm OD and 0.7mm thick walls and despite being cheap they are quite stiff and strong, I was however a bit worried that they were not strong enough for this application. looking through my junk box I found a short section of much heavier 25mm tubing and a very short bit of 22.5mm tube. A little work with a smooth file and some epoxy and I now have a much stronger first metre section.
I think it is the first section that takes the biggest load. Pardon the pictures quality.
I am hoping to get some feedback on the probable strength on 25mm tubing in a standard aluminium. Doing this will save 2 kilos. Taking the floor out will probably cut another half kilo from the weight ( If I cut it out that is)

[dopplershift]

What kind of feedback are you after?

How will this pole be loaded? I presume in a Tipi, it would be mainly loaded along its length, but with some bending around its base?

If the tube is horizontal, and supported at one end, with the load at the other end, then the calculator at the link below indicates that it could probably take a load of about 13kg.... but it all depends on how its loaded and exactly what kind of aluminium it is (etc, etc).

(measurements used for round hollow tube: 40" length, 1" diameter, 0.028" wall thickness, 30lb load. This gives a stress of about 350MPa... which is really quite a lot for most common aluminium alloys to take!)
http://www.botlanta.org/converters/dale ... nding.html

If the tube is loaded purely axially (along its length), then I would expect it to hold far more than 13kg.

Does that help?

[Moondog55]

Single vertical pole, so yes an axial load.
OK so I'm glad I made the thicker pole for the base.
Pole is 3000mm tall in total. I guess I better pack a couple of spare sections then Just in case

[Moondog55]

I just found some tables for tubing strengths.
I also phoned the local aluminium shop for some information
I have to assume this stuff is the most common tubing (3003) and most common temper ( H12 or H14 ) not very strong so it looks like it will fail by buckling at around a compression load of 800 or 900 kilos.
I am at a loss as to how to interpret than in real terms so I am just going with what I have already done and take spare sections. as mentioned in the tipi thread wrapping with carbon fiber and epoxy would probably work but postage from America is simply too expensive

[dopplershift]

Yup, 3003 alloy is pretty weak. And it is likely that what you have is something like that.

I highly doubt that it will be able to take anywhere near 800kg as an axial load. A quick calculation indicates that a more realistic failure loading for a 3m length is something like 30kg. A 25mm tube is very slender when you're talking about a 3m length! Increasing the diameter would be the best way to improve it's resistance to buckling.

I haven't seen the Tipi thread, but you can buy carbon fibre (or cheaper glass fibre) and epoxy in australia too.

[Moondog55]

It was carbon fiber tubing I was looking at and I couldn't find any
If you have any links for 20mm woven tubing I would appreciate it. I only need 2 meters
I weigh more than 100 kilos and I can chin myself on one of these; bridged across a couple of ceiling beams, 600mm spacing does the height make that much difference? I thought it was only cantilever that made the big difference. Much to learn here

I know My tarp poles are 7075 - T6 and they are 9mm and 2700 tall

[Moondog55]

OK Is there a quick and dirty way of finding out how strong ( or how weak ) these poles are? I have one spare I can sacrifice in a destruction test and can some-one help with the calculations afterward??

[Moondog55]

Well I just tried another experiment, I got a 1200 length of this tubing and put if over two beams 900 apart and put a hook in the centre with a 30 litre bucket suspended in the centre and filled the bucket with water. no problem and no visible deflection; tried chinning myself with both hands in the centre of the tube. Immediate and catastrophic failure, no bending but "SNAP" so strength is between poor and unacceptable I guess

[Moondog55]

My GoogleFu worked today

http://www.playwithcarbon.com/products/ ... leeve.html

Dearer than the US sites and shipping is almost as expensive, I've asked if they will use a 500gram prepaid.

[Moondog55]

Just found Eulers formula, explains a lot I didn't understand.
When you divide the strength and stiffness of the pole by ( 4 X length squared) every extra centimeter hurts

[Moondog55]

Another article I just read, it appears I need to take corrosion into consideration as well and should not have the CF in contact with the metal at all

http://mae.ucdavis.edu/vlasaponara/comp ... stakes.pdf

It would be easier to buy a pole if such existed, but I may have some FG tape left-over from the kayak building session of a few years ago the polyester resin has already gone off tho and got chucked a decade ago

[dopplershift]

Hey,

It sounds like you basically need a quick engineering course or a good book on "structures and materials". This will have formulae for bending, buckling, shaft design etc etc. I haven't found anything online (in a 2-second google).

I've found it hard to source woven CF tube too... most places just sell 'pulltruded' tube, which has all the fibres oriented longitudinally. That sleeving looks cool, but you could probably get a similar result by wrapping CF cloth around a mandrel and laminating several layers.

[climberman]

moondog - at http://www.bushwalking.org.au/FAQ/DIY_R ... .htm#Poles roger reckons Fibraplex may

http://www.easycomposites.co.uk/Categor ... -Tube.aspx

[Rob A]

In theory you will most likely lose the pole somewhere close to the middle, or just above or below a middle joint.
In reality it will probably go where you fall against it, knee or head but it when you are drunk.
Have a quick squiz here http://www.faculty.delhi.edu/hultendc/A ... e%2033.pdf and http://www.civil.eng.buffalo.edu/cie325 ... esting.asp
Good thing about aluminium and steel, there are so many telescoping sections you can sleeve stuff easily if you dont get it right first time. Most places that sell the stuff have the tables from their supplier (Lysaght eg), which are pretty well understood, and probably someone there knows off hand whether what you plan is likely to work. Always carbon wrap it if you were of the mind.
Anyway, if it looks right, and doesnt wobble round too much when you use it, then its probably pretty much right. Low tech is good. If you get too cute something obscure will bite you.
All the carbon will be pulltruded in small sections (often china) or spun/filament wound. Spun particularly for designed special purpose, spars, oars, paddle shafts. Gets phenomenally expensive. Larger sections like yacht masts will get a prepreg cloth laid to a design over a mandrel and baked. Really thats the same as special components, like bike frames, car parts from precision steel molds. CST has some good Aus porn and you can see prices http://www.cstcomposites.com/tubes-rods ... -profiles/ If its only for one pole you could source a paddle shaft blank. Probably the cheapest form, but its still going to cost you real money.
Id be visiting your local Alcoa if the steel winds up being too low tech, but theres a reason it was used in the first place. Cheap and works. Its failure mode is good too. Get some warning.

[Moondog55]

Thanks fellers
RobA
It is the weight of the steel pole that makes it unsuitable, I had a quote for a 3 metre, 3 layer laid up CF pole in 900mm sections, $580- plus $100- insured freight.
Rutalocura whose own mid uses a 6063 T-6 32mm pole ( but the section isn't given but could I 'spose be worked out from the weight which is just over a kilo)

[Rob A]

You arent looking at paying six or seven hundred dollars for the pole are you? I mean if you were then give CST a bell.
Their smallest yacht spinnaker pole bare carbon tube was round four hundred last I looked and at about 2800 long.
Given you would probably need nothing like that performance, they might have something less that would suit you.
If you were seriously looking at hoiking those sort of bucks at it then Id check out the local rowing clubs first and see if there is a local spar builder/repairer and chat him, or at least check whether anyone has a decent lead on tube stock.

Check these. http://www.cstexpress.com/carbon-fibre- ... ef7d2f4099
and the PDF http://www.cstcomposites.com/wp-content ... range1.pdf

Guys like Oceanpaddler, http://www.oceanpaddler.com/ had bundles of 27(?) diameter for his custom Fenn and Knysna paddles last time I was there. I think stock comes in 2750 long. Complete paddles used to go out the door $200-400 depending what sort and whether you bought it with a boat. http://www.surfskitasmania.com.au/surf-skis.html seems to be a similar kind of affair, but Ive no idea what/where he acutally carries.

Many of the boatbiulders will have a line on carbon product. But stuff like moths are coming in from china complete.

If you are only throwing a few bucks at it you can play round till you get it right. You can do that with aluminuim. If you are laying down seriousl cash you really want to be able to chat the source of the product and talk to their tech guys or guys that are doing it all the time.

[Moondog55]

Not on a $100- tent
But I would be willing to spend $100- to get it right.
As far as I can see composites are the future of this sort of tent pole.
I have been talking to some people in the know here in Geelong who build boats. for what I need FG sleeve in combination with a single layer of CF should do it, although 5 layer would be much stronger.
I want to lay this up myself, partly as an experiment and I need to save labour cost. Time I have to spare but I am cash poor.
I tried spiral wrapping with FG tape yesterday, results are ugly and if it looks bad I am sure it would perform poorly.
Soller in the USA are by far the cheapest suppliers of small quantities that I have found so far but shipping is a deal killer, USPS charges are getting higher by the month.

[Moondog55]

Well sometimes eBay is worthwhile
I just bought some lightweight 50mm CF sleeving for just a little less than half price, 8 feet for $11- Normally US$2.89 a foot.
Stretched I may have a touch left over and my information is that when the sleeve is stretched the finished pole is more resistant to bending as the fiber lay is more along the tube axis.
I am ordering 2 LW sleeves in fiberglass as well ( 1 * 25mm and the other 32mm ) so this will be a hybrid pole FG--CF--FG but should be close enough to the strength required. Heavier than a 3 layer CF pole but much lighter than a steel one. Mail will take a few weeks to get here.
To get around the issues of shipping cost I am having them sent to my sister-in-lay in NY who will repackage as a large letter and simply mail them to me

[Rob A]

Good find. Did your mates at the boat shop mention peel ply? A wrap will take a bit of the headache out of your epoxy carbon ratio, and leave you with a less sticky managable surface. You will get your strength from the carbon, Im not really sure why you want the glass in the mix, or do you mean a glass tube as a lost mandrel?

[Moondog55]

No actually the fellers at Soller said using glass was to protect the outer CF from physical damage and the inner was because it was so much cheaper than the CF sleeving; 0.99 Vs 2.99 a foot
My intention would be to test first with the cheap stuff and then make a proper mandrel from 32mm Aluminium tubing in the future if this experiment works. So as I intend to leave the lightweight tube inside the first layer of GF is partly to stop corrosion during the test but mainly for cost. the tubing I have is not smooth enough to use as a releasable mandrel. 25mm is a little on the small size I think for a 3M tube.

[Moondog55]

Just to update this.
Soller did not post the fiberglass sleeve as my pre-paid CC was a few cents short.
I went up to Falls Creek using the steel pole and as reported in the tipi thread the pole broke at a join about half way down; as was predicted by Rob A.
So basically back to square one.
How-ever in the mean time I have accumulated some off-cuts of aluminium tubing, 25*3mm, 32*3mm and just found some 48mm scaffold tube in the garage.
I only need 3050mm (10 feet) so cheapest and easiest way is to use aluminium tubing.
Thanx RobA
I have 8 feet of CF sleeving if anyone wants to play or maybe I might just make an ugly section and use that.
Almost anything will be stronger than the thin section ( 0.56mm) 25mm swaged steel pole

[Moondog55]

Yes I remeasured the steel poles and they are thinner than I first thought/measured, the swageing process deforms the tube. I have seen broom handles made with thicker steel

[icefest]

Have you considered a windsurfing mast as a centre support? They often come in 3m lengths, where you can use the bottom 2.3m for extra strength.

You can often find second hand ones cheap on gumtree: http://www.gumtree.com.au/s-ad/parkdale ... 1026786413

[bernieq]

Moondog, have you considered bamboo?

I'm assuming you're intended use of the tipi is as a basecamp - not packing up and moving each day?

I'm thinking 3 x 10mm diameter lengths duct-taped together would be very strong (and with some flexibility) and quite light-weight. Obviously a 3m length would be difficult to manoeuvre so 1.2m lengths could overlap interlaced (with a collar of appropriate diameter and length taped in place for added strength).

Just a thought ! (and certainly cheap :)

[Moondog55]

Actually I had considered bamboo. but I was unable to find any decent quality canes and gave up on the idea. to get enough strength in the top third you would need canes that would be quite thick on the bottom too but if I can find some I'm willing to give it a try.
Melbourne Botanical Gardens don't like you helping yourself

[Giddy_up]

Heaps of it up here in QLD Moondog but the freight to you might be a challenge. Let me know if you want to try a bit.


"Experience is a hard teacher because she gives the test first, the lesson afterwards"

[Moondog55]

Throw some on the top of the car next time you visit down here G.
Here is a question for the engineers amongst us, if maximum deflection occurs in the center of a slender column wouldn't it make sense to make the central third of the tent pole bigger than the rest?
Larger in diameter and / or wall thickness?.

[Moondog55]

So I just came back from Direct Aluminium with 3 sections of tubing to try.
40*1.6mm and 44*1.6mm which are a sliding fit, I was thinking to use the 40mm top and bottom and the 44mm as the center section and use either spring pins or bolts to hold the parts in place. I'd appreciate a critique of my idea. It has the beauty of being cheap and easy and not too heavy

[MartyGwynne]

sorry I just had a look at this post, I would suggest to use an old 3 piece surf fishing rod. Even two of them so you could use one while the other is just holding the tent up
I am not sure how the top part of the ten is set up if the pole extends up through it you could leave the fishing rod as is.
They are very flexible and relatively cheap for a new one but I am sure you can find some cheapies at garage sales etc.
Cheers (tight lines).

[Moondog55]

Thanx for the suggestion Marty but a fishing rod is far too flexible [ I had already thought of it and rejected the idea when I got one cheap at the recycle shop and tried it] I just placed an order at CG Composites for short section of CF sleeve

http://www.cgcomposites.com.au/index.php

Reasonable cost when you consider postage, shame they have no fiberglass sleeve. I'll post a picture of the top part of the tent when I start sewing the Kevlar into it.
I'm going to use 40*3mm tube for the base section to resist the vertical load and I will sleeve the centre section to resist bending. I just need to go and buy some fresh superglue to hold the fiberglass in place before I use the epoxy resin and CF sleeve it