When I left you last, I had a revised design which I was pretty happy with, and the next stage involves turning the concept into something practical…
This involves answering the following questions:
- How do I arrange the pieces of my tent when cutting out the fabric ?
- In what order do I then join it all together ?
- How do I actually sew the thing ?
- Will it be any good ?
The answers to these would also give me an insight into the shopping list – notably how much fabric to buy.
Arranging the Pieces
There are two main issues here – an obvious one and a less obvious one.
The obvious issue is that the arrangement of the pieces is constrained by the dimensions of the fabric. The width itself is fixed, and then I just buy as much length as I want, including a bit spare. The fabric I’m looking at using is 58″ wide (usable), or 147cm in new money.
As my panels are mainly triangles, and acute triangles (ie all angles < 90 degrees) at that, they just need one side to fit across the width of the fabric, and I then simply lay each panel end to end. Doing this is simple but results in a very long length of fabric being used, and plenty of wastage. It would be better to see if there’s a way I can alternate the triangles to use more of the fabric and waste less.
So I looked at whether decapitating the shelter so that each panel fitted vertically across the width (landscape format if you like) would work. This involved separating the top 60-70cm of each panel to make quadrilaterals. This saved around 3m of fabric length as I could invert some panels and leave less space between them.
Feeling the need to prove this out, I made a further paper model:
I realised when sticking this together that it was less fiddly if I attached the top piece to the back and side and then attached the beak afterwards. Moreover, it avoided the need to join loads of panels at the top – replacing this instead with a single overlapping seam. This looked like the way to go. The main downside was that the top piece would be a more complicated shape itself.
Furthermore, this made fitting the shapes on fabric easier, or at least more obvious.
The less obvious issue is the need to consider the stretch properties of the fabric. Tent fabrics like silnylon stretch when wet, and particularly so on the bias (diagonal to the weave). Silpoly, which this shelter will (probably) be made from, stretches less in all directions, but still has a bit of stretch on the bias. I still need to consider the orientation of the pieces to optimise the strength of the fabric and manage stretching.
After a lot of reading on MYOG fora, and a few videos watched, I came to the conclusion that I shouldn’t get overly worked up about stretch, provided that the seams where I join panels are all cut in the same direction. This means I could cut a side on the bias, provided that the edge of the next piece is also cut on the same bias. Here simply inverting adjoining sides on the layout achieves this for the most part. In addition, most panels are vertically aligned across the width (weft) of the fabric, and the bottoms of the panels are aligned on the length (warp) of the fabric. This should mean more certain pegging out too.
I then turned my attention to the thorny question of catenary cuts. There seem to be as many opinions on this as there are stars in the sky. But amongst the crowd I saw a few voices suggesting that a catenary cut is more useful on a more stretchy fabric such as silnylon. Silpoly could get away with a shallower cat cut, or maybe even none. Considering that I was thinking of using the sturdier 1.6oz silpoly anyway, which has even less stretch, I basically concluded not to bother. At the end of the day, it’s too much hassle, for my first shelter, and just another complexity to mess up.
The end result of all of these deliberations, was something like this:
This ensured all of the structural elements would align with the warp/weft where possible, or failing that ensure that joins between panels were cut at the same angle (bias). It also showed that I need around 8m of fabric if I’m careful. Although clearly I’ll buy more than that.
Joining it Up
The next stage, having finalised the exact shapes, was to create a definitive plan. In this plan, I drew out all of the panels, starting from the rear, showing adjoining panels as far as possible – essentially flattening the 3d of the tent to 2d. Obviously, when I get to the front of the tent, it doesn’t join up, but it’s pretty obvious how it does join. I also added the doors.
I’d long realised that although it is relatively straightforward to construct the shape on A4 or A3 paper, I’d need a very large set of compasses to use the exact same method on the full size pattern.
[Side note: To construct a triangle, draw one side to the appropriate scale (I used a scale of 1cm:10cm or 1cm:20cm for my models). Set compasses to the equivalent length of one side. Where that side joins the line already drawn, place the point and draw an arc of radius equal to the side length desired. Repeat for the other missing side. Where the two arcs cross is the final point of the triangle.]
When scaled up, I would have to use the angles between the sides to create the shapes, so I set about measuring every angle in my diagram. rather than physically measure it, and introduce error due to any inaccuracy of the drawing, I calculated the angles mathematically, using one of the many online calculators. Pythagoras won’t work here as these aren’t right angled triangles. It involves a bit of sin/cos/tan, and whilst I am perfectly capable of doing the calcs, it is still faster to simply plug the side lengths in to a webpage and note down the angles between each side.
However, when scaled up it will only take a very small measurement error in the angles to be quite a bit off in the final shapes. But the same could be said even if I did have a 2m span pair of compasses. Some iteration will be required to interpolate the correct vertices of the shapes. This is the other reason for making a paper pattern – if I do all of the working out on paper, then I just need to cut out on the material without having to do all the working out. I can also use a generous seam allowance to allow for a small amount of measurement error.
Having done the overall diagram, I transferred them to a slightly scaled up version on my pattern paper – each side length now being double – so 1:5 scale per side, or 1:125 overall (as it’s 3 dimensions).
I added 2cm seam allowance all round (except where I started drawing too close to the edge of the paper and couldn’t be bothered to start again), and then cut it all out.
Then I lay the pattern pieces out on some cheap poly cotton I bought on eBay and pinned in place. I then cut out the shapes.
Having cut out the fabric yesterday, I couldn’t really avoid making an attempt at the sewing today. So it was time to call in the missus for a lesson in how to use the sewing machine. Sewing machines have hitherto seemed to be a mystery kept closely guarded by the female members of the family. Every time I’ve seen them being used, they look utterly unfathomable.
But having watched a few MYOG sewing videos I picked up the functions relatively quickly, and was soon just trying out the various stitch types.
It seems my wife’s machine has a lot of fancy ways of doing zigzags. I tried them all out of curiosity, and also working on the premise that any sewing is good practice at this point. It’s highly unlikely that I’ll be using wave function stitch designs on my gear though.
I moved onto trying out a seam or two, with focus mainly on the flat felled seam.
The stitch wanders about about a bit, but I’m sure that will improve with practice. Also having straight edges might help!
We had a bit of a panic at one point when the machine just junked a whole load of the top thread under the fabric, but after much cursing and re-threading we simply swapped the cheap and nasty thread we were using out for something decent, and the problem went away just like that. Use good thread.
Having got the basic idea, I moved onto assembling my mini prototype. To cut a long story short this was an UTTER SHAMBLES.
A few things went wrong…
First some of my edges could have been straighter, which meant folding them over to create seams was a bit hit and miss. Cut out using a ruler as a guide, next time. Don’t do it freehand.
Second, I got some of my flat felled seams the wrong way around.
Third, I didn’t pull the fabric apart when doing the second part of the flat felled seam, and it just looked wrong.
Fourth, I struggled to keep the machine under control, and veered off a few times beyond the seam. Imagine your first driving lesson, but with no dual controls in the car.
Fifth, I rushed it. Probably just wanting to get it over with.
Sixth, I’d intentionally done big seams at pretty much the scale I’ll do the real thing, so they’re not in proportion and distort the shape a bit. They also make the joins a bit clumsy.
Seventh, it was just shit generally.
But there were some positives (believe it or not):
I could feel myself gaining confidence in the actual sewing bit. The hemming I did at the end went pretty well, leaving aside the knock-on effect of wobbly cutting and earlier sewing mistakes. By the end I was sewing closer to the seam edge and at a more controlled pace.
I got a decent sense of the level of detail I need in my sewing plan for the real thing – I’m going to need to work out seam by seam the order, not just panel by panel.
But most of all, it just needs a lot more practice.
Will it be any Good ?
It’s clear already that my previous thoughts as to the planning and the measuring being the key to this project were right. It feels like the sewing will get better with practice, but the way I manage the fabric and the measuring that’s needed mid-sew will be critical to getting a reasonable finish.
The overall state of play at the end of this exercise is that I’m nowhere near ready to attempt the real thing, or even a full size prototype – more practice is needed. Or to put it the way my wife did when she reviewed my efforts: “If you cut me out a set of pieces, and I have an hour spare sometime, I’ll have a go and show you what it should look like.”
There may be a short delay before we move on to the next stage, while I practice a bit more.
Or a lot.