I am going to make a 3 piece cup, now that the cups fit me well I shall see if I get a little more support with the third piece.
Then I have to test grading the pattern. Oh what fun!
First you need to know what band size, underwire/size you wear and what the diameter of your bust is. To get your band size, measure your under bust measurement. Then take your chest measurement (above bust). Take the average number of the two and round to the nearest even number. That is your band.
Then you need the bust measurement. If you want to do accurate, you need to measure each breast. Measure from your center front where the breast starts, measure across to the other side where the breast ends. I have discovered that it does not matter if you sag or don't, this amount will not change. On a sagging breast, measure from the front (looking in the mirror) from where you start to see the breast definition (even if sagging), then measure straight across to the other side where you see the end of the breast definition.
Even with accurate measuring your bust size could vary as some women aren't symmetrical. Try a sample in the side you choose and the size above what you are calculating. The charts below can get you some info.
On paper, using a ruler and a compass, draw a circle the diameter of the wire. Draw a box around it. To the right, draw a parallel line 3/8"-3/4". I used 3/8".
At the right side center, mark up a line 3/4" up on the line. If you use 3/4", go to the right 1/8" (as pictured- although I erased it in a step later because I used 3/8"), if you use smaller, keep the line where it is.
On the left, mark up 1" from the center and over to the left by 1/4". See Pic below.
I decided to split the ratio up on the band, so take your chest and under bust measurements and find 60% for the front and 40% for the back. (before I had just split it 50/50). Then take 1/2 of each measurement.
Reduce your back measurements by multiplying the back amounts by .75. Square a line out from the top and bottom lines these amounts.
Then you just need to shape the neckline and waistline. At the side seam measure about 1/4" up. Under the circle, measure down 3/8" - 3/4" (depends on the elastic you use). I used 1/2". At the CF waistline, measure up 1/4".
To find the top of the side seam, duplicate the height of the center front bridge as the side seam. Half way between the CB and the side seam crease and find the strap placement. Use your curves to make your band shape. The Cb depends on the hook and eye tape.
New cup draftTake your ruler and compass and draw a circle the diameter of the bust. Divide the circle in 4 equal parts and cut the top from the bottom.
On the bottom piece, cut down the center line but keep it attached at the circle. Open the top of the circle 1 1/2" and tape both sides down.
On the right side of the split lower it 10% of your bust diameter. Take your wire diameter, multiply it by Pi and divide by 4. Take that measurement and measure up the sides from the center slip with you flexible ruler.
On the left side, extend the line 10% of the diameter. On the lower right side, measure up 2.5% at the center point, on the left side, measure down 5% in the center and blend a curve from each point.
Before going further, measure from right tip to left tip to make sure it measrues the bust diameter. If it doesn't adjust it.
On the top right line, mark up 2.5% at the half way point. On the left side, measure up 5%. Blend and curve.
Now for the top cup. Start the top cup just like you did on the lower cup. Split and open 1 1/2". Leave the curve attached at the top. (The top and bottom have the same curve) Make sure to measure from point to point to make sure it matches the bust diameter.
Walk the lower cup into the band, then walk the top cup and mark where the cup hits the band.
Blend and create your armhole and neckline shapes.
Test and try!