all woven fabric has stretch along the 45 degree line..aka the bias. the secret if you don't want it to stretch is to cut each piece along the long or short grain.

John, are you making the umbrella cover to keep sun or rain off?

You might want to check a couple (or more) sites that carry fabrics specifically for outdoor use...
Beacon Fabric and Notions
Outdoor Wilderness Fabrics

Specifically check the Sunbrella fabrics for shade and lasting ability in heavy sun; or the nylon fabrics such as Ripstop and Supplex for rain. I have used a coated Supplex fabric and it has NO stretch. I am guessing the coating prevents stretch.

Hi Dayenu,
It's a circle, and is being stretched in 16 directions, so it's hard to not hit the bias. I suspect that nylon may not do this, but I'm going to have to check it out.
Hi Red_Confeti,
I want to keep the rain out, but I was using polyester as an experiment (it's cheap), before I use nylon, or some other more expensive (waterproof) material. I've been told that nylon, polyester, satin polyester, and pongee, are what's normally used to make umbrellas, so I'm not sure if this bias stretch thing is critical or not. One of my problems is that there is little or no information on this, and I'm not at all familiar with fabrics, so I'm really flying by the seat of my pants here. Thanks for the links.
John

it is the physical nature of anything woven, unless stabilized with a coating, to stretch on the bias. the fiber content won't make a difference, it's just a law of physics.

Is the circle one flat piece of fabric or several. If several with the straight of grain down the center the stretch is more evenly placed. Often the seams are along the spines on and reduce the stretch.

Hi Dayenu,
I thought that maybe some fabrics were woven in such a way that they have no bias? I don't know.
Hi Glassquilt,
Well, normally it would be 16 (8 or even 4) panels, but I'm trying to make it from one round flat circle, no cuts. I'm hoping that after I get the ribs attached I'll just have to dart the slack to get a taut canopy. This way I'll be able to avoid a whole lot of sewing.
John

you will most likely use ALOT of fabric when making it out of a single circle. how big is the canapy going to be?
It is really easy to make it out of panels. It is just straight sewing.
-renee

Hi Scryn
This is my first time, and to tell you the truth I'm finding it a little daunting. I calculated that if I were to cut out and sew panels I would save about 1/8 of the fabric (assuming I can use the off cut). When you cut out panels do you make a circle first, then cut panels out of it, or do you just cut the panels in whatever way will use the least fabric? If bias or web direction aren't a consideration you would probably use much less fabric than my way, cutting them from a circle. Also, do you pay any mind to web, bias, direction. The umbrella I'm covering is is 54" across, and has 16 ribs. I have just now completed my first mock up. Shows promise, but I have to adjust the tension on the ribs.
John

If you don't pay attention to the grain clothing won't hang correctly on the body. I think the same would apply in your project.

You're pie shaped pieces can be layed out side by side reversing up & down. :/\/\/\/\:

Did you ever consider buying a readymade?

To minimise stretch you need to cut each pie-shaped panel with the straight grain of the fabric running straight down the centre from the point to the bottom (round) edge. Glassquilt's layout is an excellent suggestion.
The nature of any woven material is to stretch on the bias. Kintted fabric stretches in more directions than woven fabric but has more stretch or less stretch depending on the direction.
If you want to avoid the problems of stretch you will just have to bite the bullet and cut your fabric into 16 pieces so that the straight grain runs from the centre of the umbrella to a point halfway between any two ribs. In the long run it will be easier than trying to fit one large circle of fabric which stretches unevenly :-)

Hi GlassQuilt/ColleenOZ,
You are right. In my first attempt I didn't put a lot of stress on the top and it looked fine, but when I increased the stretch I got puckers in about 4 of the panels. So I guess I'll have to, as Colleen says, 'bite the bullet' and cut out the panels. (I suspected there was a reason they do it that way, I just couldn't see why.) Funny how one can wear fabrics all his life and know so little about them. Do you think nylon will behave the same way i.e. will I have to cut panels from it? Do all fabrics have a bias?
GlassQuilt - What's a "readymade"?
John

readymade - buy the umbrella at a store.

Any woven fabric behaves that way, though the tightness of the weave affects the actual stretch. Cheesecloth vs. sheets. The weave itself can act differently, jeans are comfortable because the weave is a twill (a fabric with diagonal parallel ribs).

Hi GlassQuilt,
Thanks for the clarification re "readymade". (Just wanted to make sure.) Why not readymade? ... Well, I love umbrellas and I would like to design patterns and make my own, maybe as a hobby/business, if I can work out how to do it. So I will probably be trying to pick your brains often, if you don't mind. I am completely ignorant about fabrics, as you have probably already discovered. Next I'm going to try taking a couple of panels out of my circle and see if that gets rid of the pucker. If that doesn't fly I will resort to cutting out each panel, as you suggested. Do you think it matters if the direction of the panels is with the roll, or across the roll? Do you think that nylon will have less tendency to pucker than what I'm using (polyester)?
Thanks,
john

I'm not sure about the advantages of warp grain versus weft grain (down the fabric or across the fabric) but I have worked with nylon, both regular and rip-stop, and can tell you that it probably puckers about as much as the polyester you're working with.
Really I think you're on a hiding to nothing with this idea of yours that you can simplify your umbrella making by having it all one piece or with only a couple of seams. If it was that easy, don't you think the umbrella-making companies that have been doing this for decades would have come up with this labour-saving idea? Keep experimenting, though- I know some people learn by hearing, others by doing. Ultimately you are the one you have to satisfy.

Colleen has a real good point about the manufactures. The bean-counters won't waste any fabric.
warp has less stretch than woof
this stretch does NOT compare to the stretch that bias has

warp - threads that run lengthwise which are threaded into the loom in heddles
weft - threads that run crosswise

The heddle is the part which picks up or pulls down warp elements, creating a shed, through which the weft passes. When there are two heddles, and one is threaded with all the even warps, and the other with all the odd, you get a plain weave. Use more heddles, raise them in different sequeces and you can make brocade, tapestry, twill, etc

Why don't you practice with small circles? Maybe the size of a cake platter. Get a feel for how the fabric handles. You are talking about darts in the circle to take up the slack. They will be wide at the outer edge and taper to nothing in the middle. You will need to practice, practice, practice.

Thanks Colleen/GlassQuilt,
I have tried making my umbrella by removing one panel, i.e. I have 15 remainging..... still has stretch pucker lines, not as noticeable, but there. I also tried loosening the fabric at a few spots, where it attaches to the ribs. That reduces the pucker, but doesn't get rid of it. I don't really want to go the dart way, that would be as much work as cutting out the panels. The other reason I would like to use on piece (with perhaps one slit) is for aesthetics and uniformity of patterns; but even if I were to be able to somehow make the pucker disappear it would likely show up in any patterns I were use. I doubt I'll resort to making smaller mockups. If I did that I'd have to make a smaller mock up of the frame etc. and the fabric dynamics would probably be quite different in a smaller size. Fabric,s not that expensive anyway.
Next question is - how to sew the panels together so they show as little as possible. I'll be doing it by hand? Remember, you're talking to someone who knows NOTHING about sewing.
Thank you all for your help.
John

Hi,
I have a tent, which I believe is nylon, and am thinking of cutting up for panels. It's made of large areas seemed together. From what you have told me I need to make sure that I'm running with the warp and weft. Is there a way of telling, other than stretching, the warp/weft from the bias. I will not likely be able to cut all the pieces from one area so I need to be able to tell which is which. I'm assuming that I can use warp and weft interchangably for this purpose?
John

This is a picture of a plaid. The lines are the warp & weft. If you think diagonal that's the bias. Look closely at your nylon and you will see the same type of lines.

You should get a book at the library or buy one. That way you can refer to it as you teach yourself. Faster than waiting for an answer on online.

Here is a link that might be useful: {{!gwi}}