Prepare the draft of A line frock as explained here without extension on the shoulder line Draw new armhole
curve L-E as shown by dotted line. In this garment there is no difference between front armhole shape and back armhole shape. Curve L-E is common for front and back of the draft..
Produce the shoulder line F-L to L’ such that L-L’ = 1” to 1½”. Curve G-F is back neck line. Mark G’ on the line G-B such that G-G’=F-L’. Draw curve G’-L’ keeping the distance between the curve G-F and G’ L’ constant.The shape F-G-G’ L’ F is back yoke.
Curve F-H is front neck line.Mark H’ on the line G-B such that F-L’ =H-H’
Join points H’-L’ by a curved line, such that the distance between curve H-F and H’-L’ constant.
The shape F-H-H’-L’ is front yoke.
On the draft of the front mark point X at the intersection of the curves L-E and H-L’
Separate the yoke from the skirt cutting along the curve H’-X
On the draft of the back mark point Y at the intersection of the curves L-E and G-L’
Separate the yoke from the skirt cutting along the curve G’-Y.
Add an extra strip of width ½” along the line G-G’ of the right back yoke for seams and add an extra strip of width 1” for the left back yoke for extension along the line G-G’
Add extra ½” along the curves L’- X -H’-X-’ L’ of the front yoke, curve L'-Y-G' of the left back yoke and curve L’-Y'-G' of the right back yoke.
Add ½’ extra for seems along the curves X-X’ and Y-Y’ of front and back skirt.