Removing sleeves is a fairly easy venture. Things to consider are where the armhole hits on the body and how the armhole will be finished once the sleeve is removed. You may need to redraw the curves of the armhole once the sleeve is removed in order to raise it slightly.
Adding or swapping sleeves comes with a few more considerations. Sleeves and armholes are drafted as a pair, so you can't just grab a sleeve from another pattern and expect it to fit with no alterations. There are a lot of interconnected factors between sleeve and armhole that are important for intended design, movement of the body, or both; including: where the underarm is, how much sleeve cap is built in, how much bicep ease is built in, the armhole depth, and how much ease is built into the upper bust.
The easiest way to do this is to copy both the desired sleeve and its coordinating armhole to the body of the pattern you want to use it with. Important factors to consider are where the shoulder point hits, shoulder slope, and armhole depth. You may choose to line the two armholes up at the bottom and alter the shoulder, or vice versa. Or you may choose to center the new armhole with the old one. No matter which option you choose, a muslin will be required to achieve the correct fit.
One other common alteration you may want to make is to adjust the height of the sleeve cap and make it shorter or taller for either visual appeal or ease of movement.
Shorter sleeve caps will allow for more range of motion when you lift your arms, but will possibly have drag lines and depending on how long the sleeve is, may kick out at the outer hem.
Taller sleeve caps will have fewer or no draglines, but will not allow as much arm movement, as the bicep will hit the sleeve fabric more quickly when raising the arms.
The other factor to consider when shortening or lengthening sleeve caps is the bicep ease. Changing the height of the sleeve cap changes the measurement of the seam that sews into the armhole. You will need to increase or decrease the armhole length by the same amount that you added or took away from the sleeve cap.
Before you make any changes, measure and note these four areas:
- Front armhole
- Back armhole
- Front sleeve
- Back sleeve
You will likely find that sometimes the front and back measurements for sleeve and armhole do not match. This is because ease is often added into the sleeve cap for either visual balance or wearing ease, or both. Note any ease built into the sleeve and include that into your final sleeve cap measurements.
You may find these additional resources helpful:
- Shoulder and Bicep adjustments: These two adjustments help you get a good fit on your bodice.
- Shoulder Width, Armhole Depth, Bicep Width Adjustments
- Wide or Narrow Shoulder Adjustment
- How to Adjust Armhole Depth on a Sewing Pattern
- How to Adjust Shoulder Slope on a Sewing Pattern
- Perfect Armholes on Knits