Pyramid tent build

[Redback]

Thanks for the pics Icefest.

Just finished measuring out the cat cuts (I have a very large stencil). Will get cutting out the triangles tonight.

[simonm]

Redback - I may have missed this but what dimensions is your tent going to be? What size cat cuts did you go with?

[Redback]

Redback - I may have missed this but what dimensions is your tent going to be? What size cat cuts did you go with?

It will be about 2.5m square at the base. I went 63mm at the deepest part of the curve.

Interested to know what you are doing for the floors? I am thinking I'll go nanoseeum (then add a tub or something on top) I was going to go floorless until the idea occurred to me that a snake could come into my tent to say 'hi'

[simonm]

Mine will be about same dimensions, although I have not looked at the cat curves yet. I plan to go floorless but intend to build an inner nest for the times I think I may need it.

Snakes are very polite, social creatures.

[Orion]

I went 63mm at the deepest part of the curve.

I'm curious, how did you decide on that amount curvature?

Interested to know what you are doing for the floors? I am thinking I'll go nanoseeum (then add a tub or something on top) I was going to go floorless until the idea occurred to me that a snake could come into my tent to say 'hi'

I'm just going to have a narrow strip of perimeter netting at the base and a flap of netting for the door. I'm still trying to decide if it's worth making the netting removable. The floor will be a simple groundsheet, either polycryo or 1 mil painter's plastic.

Instead of noseeum, which is about 24 g/m², I'm going to use a lighter netting that is about 10 g/m². The lighter netting won't keep out the tiniest bugs, but where I camp it's usually just mosquitoes and maybe some flies, spiders and ants. No noseeums. And only very, very rarely do I see a rattlesnake.

[Nuts]

An inch to the ft, so say 90mm to the meter of seam length? from square to the apex of the catenary cut. I read this somewhere , for me it still wasn't quite enough.

The way I understand Catenary (/shelters) is that it describes a cut taking into account the weight of fabric.. ie. deeper towards the ground for a tipi side-seam, pretty close to an evenly shaped curve for (say) a tarp ridge seam with equal height ends?

[Maelgwn]

There is ALOT of banging on about caternary cuts and how much the curve should be on backpacking light. There is also a Roger Caffin excel spreadsheet with the calculation floating about on the internet somewhere too.

BUT - in many ways getting in perfectly correct is not really important. Due to stretch of fabric and typical seam tolerances etc, any amount of curve that looks above right will work and will make the fabric sit pretty well. Stuffing around getting it more exact than that does not really improve anything in real world scenarios.

PS - I reckon a piece of ply/mdf than you can stick pins into is the way forward when trying to cut/measure/pin your fabrics. But it still wont be millimetre perfect.

PPS - Removable perimeter netting is a cool idea but IMO too fiddly. Hard to imagine a lightweight bug proof way to achieve it. Velcro would be the obvious way, but it's not that light and would fill up with dirt. You could probably do it with those very light plastic press studs but would be very fiddly to make the join bug proof.

[Nuts]

Maybe the curve matters less with nylon, my figure may just be for Cuben? Yeah, i'm sure it doesn't need to be precise but there was a sweet spot.
It was pretty obvious once built that a bit more curve would help keep the fly taught/er (it's easy to pinch up some material to see). It was easy to recut a deeper curve.

A mdf sheet yeah!, once the fabric is pinned out a long metal 'straight edge' can be pinned (brad nails) at several points around a curve too for a close cut...
made easier with a hot knife

Sew in a 'perimeter net' would be easiest? (seems to keep most things out)

[Orion]

There's definately a weight cost to making something removable. But for times where it isn't needed, or times when it would be a problem (e.g. snow in the case of permeter mesh), it might be worth that cost. One has to consider the intended usage of the shelter. For one tent I used paper clips to attach the temporary lightweight netting we needed for a really bad mosquito situation. That worked really well.

[Orion]

Maybe the curve matters less with nylon, my figure may just be for Cuben? Yeah, i'm sure it doesn't need to be precise but there was a sweet spot.

So what is this magic sweet spot curvature for Cuben seams?

[Nuts]

Lol, somewhere slightly greater than 1"-foot.. (I don't know.. as I say I tried 'someone's' magic formula and found it was missing a smidgeon )
PS. Coming to remember the conversation, I do recall nylon was cut with less curve (probably not a great deal less) A good starting point for something similar to commercial designs would be to have someone measure the curve (ie someone with a duomid) with a straight edge to get the deepest measurement of the curve.

[Maelgwn]

There's definately a weight cost to making something removable. But for times where it isn't needed, or times when it would be a problem (e.g. snow in the case of permeter mesh), it might be worth that cost. One has to consider the intended usage of the shelter. For one tent I used paper clips to attach the temporary lightweight netting we needed for a really bad mosquito situation. That worked really well.

A quick look on the internet seems to show velcro can be found at about 8g/m (http://www.zpacks.com/materials.shtml). So assuming a 10m perimeter, this would be 160g when the netting is in use and 80g when not in use.

The blingy 10g/m2 netting you are proposed (generously assuming 50cm all around) would weigh all of 50g! And could be tied up with little bits of cord (or paperclips!) when not in use - i.e. the snow.

Unless i just stuffed up my maths - it seems heavier under all circumstances to make it removable?

[Nuts]

10g, it must be very flimsy Orion, I can see why you want it replaceable
You can bond mesh between two pieces of cuben with contact adhesive, I used spray adhesive, it worked well...

Have you thought about the angle of the mesh or just using velcro to join it at each corner (to itself)? If cut wider or you could separate the corners you could pull the mesh out to use as a snow valance (though i'm not sure how such light mesh would handle any weight..). Everyday noseeum mesh is surprisingly tough.

Perimeter netting wont be that easy to do (attached or removable) if you catenary cut the lower hem but adding some curve here keeps the material nice and tight lower down, between the pegs. You might find it easier to build (and replace) your netting skirt if attached/sewn to a straight strip bonded to the inside of the fly rather than attached/sewn around the hemline?

[Redback]

There's definately a weight cost to making something removable. But for times where it isn't needed, or times when it would be a problem (e.g. snow in the case of permeter mesh), it might be worth that cost. One has to consider the intended usage of the shelter. For one tent I used paper clips to attach the temporary lightweight netting we needed for a really bad mosquito situation. That worked really well.

A quick look on the internet seems to show velcro can be found at about 8g/m (http://www.zpacks.com/materials.shtml). So assuming a 10m perimeter, this would be 160g when the netting is in use and 80g when not in use.

The blingy 10g/m2 netting you are proposed (generously assuming 50cm all around) would weigh all of 50g! And could be tied up with little bits of cord (or paperclips!) when not in use - i.e. the snow.

Unless i just stuffed up my maths - it seems heavier under all circumstances to make it removable?

I am looking at making the netting permanent, with the bathtub floor removable. If the skirting is large enough, I think it should fit in underneath the tub (maybe some elastic and mitten hooks to hold it)

[Redback]

I'm curious, how did you decide on that amount curvature?

I used the spreadsheet to calculate it. Roger Caffin

I'm just going to have a narrow strip of perimeter netting at the base and a flap of netting for the door. I'm still trying to decide if it's worth making the netting removable. The floor will be a simple groundsheet, either polycryo or 1 mil painter's plastic.

Instead of noseeum, which is about 24 g/m², I'm going to use a lighter netting that is about 10 g/m². The lighter netting won't keep out the tiniest bugs, but where I camp it's usually just mosquitoes and maybe some flies, spiders and ants. No noseeums. And only very, very rarely do I see a rattlesnake.

One snake is more than enough.

[Orion]

The 10 g/m² netting is actually bridal veil from the local fabric store. It sounds like it would be flimsy. In fact it isn't very stiff so it doesn't work very well for a door with a zipper. But it is surprisingly durable as general purpose bug netting. I wasn't thinking of making it removable so I could replace it. I would simply like to be able to leave it behind when unneeded/unwanted.

I know velcro isn't very light, but a continuous strip of velcro wouldn't be necessary. But I already suspect that it won't be worth making it removable. It's just something I plan to look at more closely before sewing or bonding the netting into place.

[Orion]

Lol, somewhere slightly greater than 1"-foot.. (I don't know.. as I say I tried 'someone's' magic formula and found it was missing a smidgeon )
PS. Coming to remember the conversation, I do recall nylon was cut with less curve (probably not a great deal less) A good starting point for something similar to commercial designs would be to have someone measure the curve (ie someone with a duomid) with a straight edge to get the deepest measurement of the curve.

Interesting. I was hoping to move in the other direction, less curvature. But I don't really understand the problem very well.

[Mark F]

My understanding of catenary cuts is that you need more catenary for stretchier fabrics. For cuben, being quite inelastic, I am planning on 20 - 25mm over 1.2 to 1.5 metres which is the longest panel edge on my design. For Silnylon I would move towards 30 - 40 mm per metre. 1" to the foot seems excessive. The edge length on a 2.5 square pyramid 1.2m high is about 9 feet so the catenary would be 9" or 230mm.

[Redback]

My understanding of catenary cuts is that you need more catenary for stretchier fabrics. For cuben, being quite inelastic, I am planning on 20 - 25mm over 1.2 to 1.5 metres which is the longest panel edge on my design. For Silnylon I would move towards 30 - 40 mm per metre. 1" to the foot seems excessive. The edge length on a 2.5 square pyramid 1.2m high is about 9 feet so the catenary would be 9" or 230mm.

As cuben doesn't stretch, less curvature is needed. It is still good to have it though, as it increases wind deflection.

[Nuts]

Lawson Kline (?), he was building tarps commercially, i'm pretty sure 1"-ft came from there. It seemed a bit excessive on paper but in reality (for my design) wasn't quite enough.

I'm sure it depends a lot on where the curve is, on my (2-pole) design the deeper the ridgeline (catenary curve) the less force needed pulling the poles apart (get everything tight). I re-cut this one a fair amount deeper than 1"/ft. Started with no curve on the hem but the loose material was obvious in a clear arch between the pegs.

It does make sense more stretch- more curve. I haven't designed one for nylon, was thinking it might take less (something else I read on the net..) as the stretch would account for some 'taughtness' already.

For a home design there is going to be some art to it. It's not impossible to re-cut curves (at the cost of a bit of tape).. so not much is 'un-tweekable'. Unless doing a direct 'copy' of something else this notion might be worth keeping in mind as you approach each stage of building.


Interesting projects, some aiming a lot lighter than mine. C'mon, this thread needs pics

[Orion]

My understanding of catenary cuts is that you need more catenary for stretchier fabrics. For cuben, being quite inelastic, I am planning on 20 - 25mm over 1.2 to 1.5 metres which is the longest panel edge on my design. For Silnylon I would move towards 30 - 40 mm per metre. 1" to the foot seems excessive. The edge length on a 2.5 square pyramid 1.2m high is about 9 feet so the catenary would be 9" or 230mm.

That's even less than I was thinking of trying. How did you arrive at that number?

Nuts (via Lawson) is recommending about 5 times as much. That's quite a difference.

My thought is that aside from accomodating stretch the curvature of the seams is there to compensate for errors made in cutting and joining the panels. In particular it would be difficult to cut the panels pre-tensioned. So if you're sloppy you might want to make the curves more pronounced. At least that's what I imagine. But how much is enough? I don't want to overdo it because it affects the head room.

[Mark F]

I agree with Orion. We need to ask what is the purpose of the catenary cut? In my view it is to prevent the central sections of fabric adjacent to a seam becoming floppy when under tension. The seam with stitching and multiple layers of fabric is likely to stretch less than the single layer of fabric either side of it. The catenary cut pre-tensions these areas and reduces/removes the sagging. It also compensates for irregularities in the seam.

As to where my number came from - I read of somebody building a tent like the one I have planned who constructed a version with no catenary in the seams and after pinching the fabric together and clipping with pegs thought that about 20-25mm would be an appropriate catenary in a 1.2 - 1.5 metre long seam. I will experiment myself before committing the knife to cuben. Unfortunately I cannot find the article.

[Nuts]

The taped/reinforced joins (I mentioned earlier) running over the top (or some similar way to join the peak.. even temporarily.. and you can pitch before committing to the finished peak 'hood' and the tie outs (temporary tie outs pegged or I nailed the base of the fly straight onto crossed timbers) Its really the completed peak and tie outs that make fixing things/ re-cutting seams more difficult (and take most of the build time).

So I guess the point is- It's not the end of a Cuben dream if all said and done, things are still annoyingly Saggy!


I see what you guys are saying, 'some' curve takes out any potential for saggy bits. I had to recall puckers while sewing a nylon seam, Cuben seams don't really need to be anything other than perfect/ like a factory edge (even in my hands..)
(unless perhaps you go trying to sew the stuff ; ) )

[Redback]

I think for Cuben it is more about the wind deflection than sagging. One other advantage is I have freed up some more cuben for seams-overlays.

[Orion]

Mark, so your "magic number" is also handed down from somebody else's experience?

I mocked up a Duomid in two sizes, both with straight seams (no curve).

The first was a 1:12 scale model in paper:


The second was a full scale model in 3 mil polyethelyne. I cut and taped those panels together very hastily:


While the paper model worked just fine without catenary (or even a supporting pole!) the plastic model really made it clear to me how saggy the pitch could be. You can't really see how much sag there was in that picture because of the way I pulled one of the stake points out with the door open. It reminded me of a friend who attempted to reproduce her beloved Chouinard Pyramid tent and her first mockup pitched so poorly she gave up. She didn't even know what a catenary cut was but was too flustered to make a second attempt when I mentioned it.

When I made a silnylon tent a couple of years ago (modeled after the Tarptent Moment), in order to get the right cut for the curved fabric I simply draped it over the pole and then used clothespins to hold it in place while I tensioned it and marked it. With my plastic Dumoid model in that picture I used clothespins again and had to pinch off about 2 inches from each of those poorly cut panels in order to get a reasonably taut pitch.

Nuts, I'm not 100% sure I understand what you are suggesting but I do see ways to tweak the design even after putting it together. I'd rather avoid that if possible.

Since we're currently starved for pictures here's one of the inside of my model showing how far off center the pole can be and still support the tent just fine:

[Orion]

A quick look on the internet seems to show velcro can be found at about 8g/m (http://www.zpacks.com/materials.shtml). So assuming a 10m perimeter, this would be 160g when the netting is in use and 80g when not in use.

The blingy 10g/m2 netting you are proposed (generously assuming 50cm all around) would weigh all of 50g! And could be tied up with little bits of cord (or paperclips!) when not in use - i.e. the snow.

Unless i just stuffed up my maths - it seems heavier under all circumstances to make it removable?

The 8.4 g/m is for both halves of the velcro. Also, a Duomid perimeter is closer to 8.4m, so it would be 71g of 13mm velcro for full coverage.

On another project where the velcro would be stuck/unstuck rarely and was not called upon to support much tension, I cut the velcro in half lengthwise. It does fray a bit this way but if the velcro is mostly left alone it works okay. If in addition to this the velcro coverage were intermittent, say 25%, then the weight of the velcro would drop by a factor of 8 to only 9g total. It may be feasible to use even less velcro, maybe only 5g worth. And of course the uninstalled weight would be half that.

So I think it's possible to do this, although I'm still not sure I will bother.

[Nuts]

Maybe 'Snaps'?

I got bored with paperwork this morning and started doodling on your image (nice shed, like the sportsmans wall )

Screen Shot 2013-10-24 at 2.16.43 PM.png (549.85 KiB) Viewed 21460 times

At some stage i'll finish the shangri-la this way, for my little tent I found that if you can stop the cuben sheet at the botom of the mesh peak there was enough width in the cuben roll to cut the triangles 'sideways' ie and have less wasted fabric (in that case).

What I was thinking earlier Orion was that you could actually build the shelter just that way (ie use the cuben itself for the mock up)
- blue painters tape holds cuben, comes off easily. Carefully get it set up then pinch/measure the catenary then lay it out and cut (not that you need to now). Lots of ways to skin (or measure) a cat.

[andrewa]

I agree with Nuts. Play with the real stuff. It's completely different to paper and builders plastic. And the most likely outcome is that it will work out, or it needs a small modification. There's a lot of anxiety about using expensive fabrics, mostly unfounded. It's rare that you can stuff it up so much that is is insoluble, and, if you trash 2 m of fabric, its only $70.....a tank of petrol, 2 cheap slabs of beer, 3/4 of a lift pass skiing, 4 Viagra tablets etc.

A

[Nuts]

Strewth, Viagra aren't cheap

I'd still do the cutting/joining the conventional way. Decide on the curve, lay out the Cuben on a clean flat surface, cut, clean, join, roll.
It's more the concepts from working with the materials that I found myself searching for at each stage.
I agree, it's likely to be all pretty straightforward with a simple design (for the main fly sheet at least..)

Ultimately, if you are at the stage where your using the shelter and don't like something you'll have the skills to just cut it off!

I took a lot's of pics of joining, attaching hood and tie outs, cutting curves etc. I'll try to track them down. No expert and some of these things can become (perhaps need to be), self-evident very quickly.. many different design options to achieve the same thing.. but If anyone needs any help, even six months away, just send a message.

(and i'm happy splitting the topic if you'd like to keep it for your build simon?)

[simonm]

Nuts - happy to leave it as it is - much more entertaining and informative than if it was just my build . Besides mine could take a while, I keep coming up with new projects .