How to measure for custom tent poles

MtnGeekUK

13/05/2012 at 22:06

Hi all,

Have decided to build my own tent and need some advice.

I know how long I want the tent to be, along with how high I want it at the tallest point, but due to the flex of the poles, don't know what length of pole I need to get.

Any advice or suggestions gratefully received.

StoneHuggingHippy

13/05/2012 at 23:19

Until you get a definitive answer amuse yourself here.

Include a little history in your walks. Pecsaetan - Ancient Derbyshire, Staffordshire and South Yorkshire - http://pecsaetan.weebly.com/

StoneHuggingHippy

13/05/2012 at 23:37

I can't do the maths, but maybe this can.

Include a little history in your walks. Pecsaetan - Ancient Derbyshire, Staffordshire and South Yorkshire - http://pecsaetan.weebly.com/

MtnGeekUK

14/05/2012 at 07:07

Think your second link does it cheers, unless anyone has any better suggestions?

Guy Hurst

14/05/2012 at 08:19

Looks like quite a challenge. I reckon calculating the length of the pole will be simple compared with working out the size and shape of the tent panels, and then sewing them.

MtnGeekUK

14/05/2012 at 08:34

Hi Guy,

I thought working out the pole length woukd be the tricky bit!

Shape is quite straightforward.

They'll be quite a few prototypes before tge finished article- as much as anything for some sewing practice!!!

Zuma

14/05/2012 at 08:45

You could prototype with electrical piping

MtnGeekUK

14/05/2012 at 09:09

Zuma,

Sounds a great idea (and cheaper than buying more than one set of poles!)

What do you mean by electrical piping?

StoneHuggingHippy

14/05/2012 at 14:28

Have a look at Stuarts myog tent here for ideas.

Include a little history in your walks. Pecsaetan - Ancient Derbyshire, Staffordshire and South Yorkshire - http://pecsaetan.weebly.com/

Zuma

14/05/2012 at 16:04

I did mean electric tubes which you use in buildings for elecrical wires. They are quite flexible

cathyjc

14/05/2012 at 17:11

When I was tent making (many years ago!!) I started with the pole I happened to have and built the panels around that. It's much easier to alter the fabric dimensions, than the pole length. Holding the pole it the shape I wanted whilst I measured the panels was tricky.
A bit a 'trial and error' method. It worked.

captain paranoia

14/05/2012 at 17:51

The BPL thread that twiglegs linked to gives some idea of the problems of trying to work out the shape of bent pole tents.

If you really want to make a tent with curved sides and flexible poles, then you're going to have to use some cunning maths, or find the answer empricially, as suggested, using cheap materials that behave similarly to the desired pole (e.g. small bore polythene water pipe), starting with a final pole and fitting the design around that (as cathyjc suggests), or starting with a longer pole than you will ever need, and cutting bits off it until it fits into your tent.

If you use the fixed template method uses by Stuart in twigleg's second BPL link, you will have to find some way of estimating the shape of the bent hoop, when loaded by the tensioned flysheet. If your model is wrong, you end up with a poorly-tensioned flysheet like this:

../../../../../../../../../../../../members/images/10187/Gallery/tent1.jpg

MtnGeekUK

09/01/2013 at 23:05

Entered Values Calculated Values Width of Arc (m) Height of Arc (m) Radius of Arc (m) Length of Arc (m) Angle Subtended by Arc (deg.) 3 1 1.62500 3.82202 135

So is this suggesting a nee a pole of 3.82202 metres? (Roughly)

MtnGeekUK

09/01/2013 at 23:25

Sorry, try again - looked fine in the preview window - hope this comes out ok?

http://s4.outdoorsmagic.com/members/images/9097/gallery/untitled_0.jpg?width=350

captain paranoia

10/01/2013 at 12:28

That's assuming a perfectly circular shape for the bent pole. As explained earlier, bent poles don't form simple circular arcs.

But, as a first-order approximation, it will probably do.

The problem isn't really the length of the poles, it's the shape of the tent panels that will cause the problems shown in my saggy paper tent above. The ends of the poles can always be trimmed to length (provided you make them a little too long in the first place...). If you assume a circular arc, your panel shapes will be wrong, and the tent will have baggy and over-stressed areas.

MtnGeekUK

10/01/2013 at 12:47

What I was going to go for was circular arc poles, but rather than having sleeves, use the Vaude model of tensioned elastic on hooks - would that not solve both problems?

captain paranoia

10/01/2013 at 18:37

It might give you some wiggle-room, and you may be able to adjust the elastic length to maintain a good fly sheet tension.

But, unless you pre-curve the poles, you're unlikely to get a circular arc. Even then, the loading is likely to distort a pre-curved pole.

You can experiment with pole shapes by taking a piece of stiff, but flexible material and bending it into a hoop. If you like, you can then trace the outline onto a piece of paper. You might plot the shape of the curve, and stick it into a curve-fitting tool to see if it can find a polynomial equation, but my recollection is that beams bend with some obscure trigonometric functions. You might google for the shape of a stiff beam fixed into a wall, with a load attached at the end. This will give a reasonable model of half a symmetric pole hoop, with the wall being the point at the centre of the hoop.

Even with this shape, the stressed fabric loading will change the hoop shape again; we know from empirical experience that an erected hooped tent can be quite easily distorted by hand, so not much force is required to change the hoop shape.

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