hi guys
all blooming day i've been trying to get a little more accurate
making round bottom bags.
I can make round bags thats not the problem, i cut the base and the body
start sewing the base about 2" from the edge and go all the way to the other edge.
then join the body and complete sewing the base. Easy..
today i thought if i calculated the circumference of the base I could
add 1" to the circumference and a 1/2" seam allwance to the base then
it would be easy.
I thought I could join the body before adding the circle base as i'd
been as accurate as i could be by measuring everything in advance.
Hah ! if only it were that easy.
has anyone else come across this ?
Yes circles are a bitch. An 1/8" off on the diameter will have a huge effect on the circumference.
If only there were some formula or something that could be used to figure it out exactly.
But then you'd have to sew *precisely* a 1/2" seam around the entire circle, or else that formula would be worthless anyway.
I know the trouble I've made duffle bags or the tube sock over a ski pilon ect.
I normally sew the body then add the base
I have to make a bag today so i might try what Peppy suggests and take 1/8" off the base dia and see how it goes
Allan
I sew a lot of bolster pillow covers. It's like a bag but with a bottom on both ends. LOL.
The zipper runs the length of the bolster pillow.
I use pi to figure out what I need to cut. I almost always put welt cord on the ends (the circles).
If I have a 6" diameter x 18" long bolster pillow cover. I use 1/2" seam allowance.
My circle is 7" (seam allowance). 7 x 3.1415 = 21.9905 = 22" + 1" = 23" for my width of the fabric panel.
I take pi out to 4 decimal places in case someone is watching me - it makes me look smart.
I now have two circles with a 7" diameter and a fabric panel 19" x 23".
I sew 3" in. along the seam allowance line, from both ends on the 19" sides, sewing the two 19" sides together. This is where my zipper will go. I put in my zipper.
I now have my two 7" circles and a fabric 'tube' that is 19" long and 22" round.
I usually sew the welt cord, the fabric panel, and the circle together with one stitch.
The secret is to notch the welt cord a lot, more for smaller circles, use a small stitch length, and go really slow.
Most problems are with the fact that the circle has both warp, waft, and bias sewing. You really need to not have any stretching.
On really stretchy fabric I will iron on that fabric backing stuff. That really helps.
Going in Circles, Three dog night.
gene
gene if i was that smart in math i would not be in the upholstery buisness :o ;D
I thought i'd gone one better, i made an excel chart up
with end diameters from 4" to 30" and every circle had
the circumference with and without seam allowance and
even the metric equivalent.
the idea was to hang up a laminated chart so any round
bag etc i wanted to make would have all the dimentions
in front of me.
still cant get it to work by making the tube first.
if anyone want the excel file to look it over pm me your email.
(https://forum.upholster.com/proxy.php?request=http%3A%2F%2Fi120.photobucket.com%2Falbums%2Fo194%2Ffragged8%2Fth_4dde86cb.jpg&hash=1cf93eca4b495be53c26547fc3bb6065) (http://s120.photobucket.com/albums/o194/fragged8/4dde86cb.jpg)
Rich
I always use the 'pi' formula like gene, but add 2" to the tube and sew around the bottom circle then join the side seams after and cut off any excess..
thats not a problem using pi but the chart I made
already has pi in the equation so it should just be a case
of reading off the numbers.
the excel file has the equation built in so if i change
the circle diameter the circumference changes accordingly.
I still cant sew the tube first then add the base after though :-)
Rich
Rich
Watch the sailrite video for making winch covers
It shows you how to do it by making the tube first
That is the process I used yesterday without a problem and I have always done it that way without a problem
Allan
hiya
I had a look Allan, i did have a 1/2" line marked to follow
but i didn't staple it all. Guess what i'm doing tomorrow :-)
Quote from: gene on May 25, 2011, 05:19:02 pm
Most problems are with the fact that the circle has both warp, waft, and bias sewing. You really need to not have any stretching.
This is what bites you in the butt. Gene is right on with this observation. Staples are an upholsterer's best friend 8)
June
Having replied to this topic with my awesome mathematical calculations and my boasting of my great abilities to make bolster pillows, today, OF COURSE!, I sat down to sew the !@#$ down proof ticking fabric to make a down bolster pillow insert and I was a full 1 1/2" off. LOL I'm glad no one was around.
I didn't even want to start measuring the mohair fabric.
Sometimes laughing just saves time over crying. And it's a lot less painful than banging my head on the wall.
gene
hehehe thanks for the feedback gene ;D
you should have printed my chart off :P