Dear JS,
Coat v jacket? The body of a jacket is 1/2 to 1 inch smaller on the sides than a basic coat. The neckline is 1/8 inch smaller than a coat. You must raise the armhole to accommodate shoulder pads, the amount depending upon size of the shoulder pads to be used. The shoulders are extended and deepened by 1/8 inch, and of course the length has to be adjusted. You always start with a basic shape before doing details.
Here's how to take a one-piece jacket sleeve, and turn it into a two-piece. You must have a jacket sleeve, NOT a shirt sleeve to get the correct shape. Measure across the pattern (seam lines, not cut edges--it's easier to remove the seams before starting), at the bicep (underarm), elbow and wrist. Divide each measurement in thirds, and mark dots on the pattern. Draw lines to connect the dots on both sides, and extend the lines at the underarms upwards, keeping the same angles. Now, fold the pattern along the lines you just drew, and trace the underarm section within the center third of the pattern. This is the under sleeve. Don't cut it out yet.
For the upper sleeve, measure out from the center third just completed
2-1/4 inches at the underarm, 2 inches at the elbow, and 1-3/4 inches at the wrist. Draw lines to connect these dots.
Before cutting, measure up on the under sleeve 1-1/2 inches and put a dot. Do the same thing 1-1/2 inches down. This is the area that needs to be eased. Mark the upper sleeve in the same way, only 2 inches in each direction. Trace one of the pieces before you cut, so that you will have separate upper and under sleeve sections. Draw short lines to make into notches; two on the back part of the seam; two in the back cap, one on the front cap. To give even more shape to the sleeve, cut each at the elbow, and open about 1/2 inch along the elbow side, so that the shape is definitely bent at the elbow towards the front. You will be opening one side, while the part closest to the front is still attached. It will look like a dart.
Measure across the undersleeve at the underarm. Then measure the upper sleeve at the underarm. The two pieces should total the original measurement before you started drafting. If they do not, adjust the upper sleeve equally on both sides until it does.
Teri