Sep. 2010 15

How to sew a cone

It’s no secret that I’m an engineer. I’m probably more proud than I should be about my totally geeky profession, but it works for me. There are some pitfalls when it comes to the mind set of an engineer.When it comes to geometry and math, it must be done right. Don’t get me wrong, I drape, cut to fit, estimate and “make it work” like the best of them but somethings just need to be done right.  If you think math and geometry has no place in crafts, then you have never quilted.

Let me explain the frustration. Recently my eldest sister decided to make a reading tent for her daughters. You’ve seen them before. They kind of look like castles and you hang them from the ceiling. Well, when Kellie realized that having 3 kids under the age of 2 didn’t leave her much time to do sewing projects, I offered to finish it for her (pictures to come later). I looked online at various blogs who had tutorials and I was blow away by the lack of accuracy in making the upper cone portion. I can’t tell you how many just said “cut a circle and adjust to fit.” That’s a giant waste of fabric! So here it is, the right way to make a cone!

A couple variables first

H: The total height of your cone

S:  The length of the sloped side. If this were a triangle instead of the cone, this would be the length of one of the sides.

D: The diameter of the base (circle). If this were a triangle instead of a cone, this would be the length along the bottom of the triangle.

Ok, so now you need to figure out what kind of cone you are going to make. Is it going to be short and fat or tall and skinny? The easy way to figure this out is to compare the diameter of the base to the height of the cone.

For each option, you’ll need to calculate S. Don’t roll your eyes at me. I have a way to cheat. Use this site. For side A type in your value for H. For side B type in your value for 1/2D. Press calculate and side C is your value for S. Moving on…

Here’s option 1. This is a short, fat cone. Your cut out should look something like this. It should be more than a half circle, but less than a whole circle. (If you don’t have Pi on your calculator, use 3.14)

Here’s option 2. If H is equal to D, your cut out will be exactly a semi circle (well, plus seam allowance if you are sewing). Bonus on this on, you don’t even need to calculate Pi * D.

And here’s option 3. This will be a tall, skinny cone. It should be less than a half circle.

Ok, no go forth an make cones correct, the first time, with out guessing….

-Very respectfully,

A very geeky crafter (Jenny)

11 Responses to “How to sew a cone”

  1. Mark Hait
    April 1st

    I want to make a short fat cone, but I think some of your calculations are missing on this site. Can you please explain. I calculated for “s”, but how does this translate for how much of a circle I need? I understand a semi-circle, but how do you figure out what size of more than a half circle you need for a short fat tipi?
    For me, I want a 6′ height and a 8′ diameter.
    Thanks
    Mark

  2. April 2nd

    Mark,
    Thanks for pointing that out! Apparently some of my pictures which were included in the original post were no longer attached. If these don’t help let me know, and I’d be happy to draw up exactly what you need to do including all the measurements.

    -Jenny

  3. Susan
    December 6th

    I also am confused about calculating for slope. This sentence in your instructions doesn’t make sense to me either: “For side A type in your value for H. For side B type in your value for 1/2D. Press calculate and side C is your value for S.” Side A of what? Side B of what?
    I am doing a small craft project with a height of 24″ an diameter of 14″.

  4. December 6th

    Susan,
    The “Side A” and “Side B” refer to the drawing if you follow the link. http://www.csgnetwork.com/righttricalc.html
    Hope that helps!

  5. December 9th

    Thanks so much for this, it is exactly what I was looking for!

  6. Kate
    August 13th

    So using the formula she had above here’s how to figure out exactly how many degrees of the circle you should sweep/cut: big circle circumference C=2*S*pi, small circle circumference (bottom of the cone) c=D*pi Then finally the degrees of the big circle you need to sweep = (c/C)*360 = (D/(2*S))*360 …make sense? :-)

  7. Chris
    March 20th

    I’m trying to make a cover for an artificial Christmas tree. The height is 90″, the length of the sloped side is 96″ and the diameter across the base (the widest part) is 60″. I measured a circumference around the widest part to be about 189″ if that matters. I measured all this with a tape measure.

    Using that other site you recommended, I calculated “S” to be 96″ but not sure I’m doing this correctly. I had already hand measured it to be that same dimension so I guess I did it correctly.

    I have one piece of fabric that is 349″ long x 60″ wide.

    I can cut this in-half (along the 349″ length) and then I’d have two pieces that are 174.5″ x 60″ and then join them along the long edge, giving me one piece that would be 174.5″ x 120″.

    I think that’s the way to get the biggest rectangle out of what I have.

    pi is very confusing to me as I never too geometry and am bad at math. I took 60*3.14 = 188 which I guess is pi? This is almost what I hand measured as the circumference of the base of the tree. Maybe I don’t need to calculate pi since I hand-measured what I need already.

    So, the questions I have are:

    What’s the best way to cut/join the fabric I have to get the piece that I would then need to cut for the cone? Is my 174.5″ x 120″ idea the best to then have one piece that will fit my requirements for the cover?

    How would I draw a semi-circle accurately on a piece of fabric? My thought was to use a piece of string, held at the base and hold a piece of chalk in the other hand, guided by the free end of the string.

    How would I know where to end the semi-circle? Does the measurement along the circled edge need to be 189″ to end up with a 189″ circumference cover? If I need to have that circular edge be 189″ I don’t know how that would happen when the piece of fabric will end up being only 96″ tall.

    Thanks for any help.

  8. xoupt
    May 13th

    I love you (not like that). Thanks.

  9. Jenni Underhill
    June 27th

    I am trying to sew a large cone shape for a cover for a 3 tiered chandelier for a friend. The height needs to be 9 ft and I need both end to be open not just one. The top of the cone circumference is 21′ and the bottom opening circumference needs to be 14′. Any help helps! I’ve sewn together drop cloth canvas from the paint department at the hardware store and have a rectangle of 12′ by 23′. 
    Thanks!
    Jenni

  10. Jenni Underhill
    June 27th

    I guess what I’m actually attempting to make is a tapered cylinder… 

  11. Bud Wintcher
    April 10th

    Jenny, my trig is a little rusty and my sewing skills even more so. I’m trying to make a replacement cover for my backyard standing firering from canvas. The
    ring is 30 inches in diameter and stands 16 inches tall. The height of the cone shaped removable cover is 10 inches and it is also 30 inches in diameter. I drew a 30 inch circle on cardboard, found the center and inserted a 10 inch long stick. From the top of the stick to the circumference line is about 18-1/2 inches. From your above illustrations, I think I need to cut a 37 inch diameter circle of canvas, measure a 19 inch arc along the circumference (to allow 1/2 inch overlap for hem on each edge) and then cut to the center from each end of the arc. Will that give me a 10 inch tall cone with a 30 inch diameter base that I can sew to the separate side?

    Thanks, Bud

Leave a Reply