Setting in sleeves and having them look totally perfect on your body is challenging to say the least.  Why?  You are taking a flat piece of fabric, cutting a shape with opposing curves and placing that sleeve into a 3-dimensional armhole to go over your 3-dimensional rounded shoulder and underarm.  To give this flat sleeve pattern 3-dimensional shape, we use underarm seaming, basting stitches and ease. 
How much ease should the cap have?  Well, you can see it all depends on many of the above factors.  
When sewing your trial bodice muslin, the back sleeve cap should have approximately 5/8” – ½” (1.6 – 1.3cm) while the front should have approximately 3/8” – ½” (1.0 – 1.3cm) ease.  If you end up with a little less or a little more, don’t worry about it.  Depending on the fabric you’re using to stitch the test, the ease may just be fine.  And, part of this will depend on your sewing skills.  There is a video tutorial on setting in sleeves – just follow this link – How to Set in the Sleeve - D.8.d Pt. 4-How to Set in the Sleeve.  This of course is just one of the ways to set a sleeve in; you may have your own preferred technique. 
Now it’s time to check how much ease the sleeve cap has.  Measure the armscye curves from underarm point #2 to shoulder point on both front and back bodice.  Then measure the sleeve cap from back underarm point #2 to cap notch and front underarm point #2 to cap notch.  Stand the tape measure on edge to do this.  Compare back cap to back armscye length and front cap to front armscye length.  You’re looking for approximately 5/8” – ½” (1.6 – 1.3cm) ease in the back while the front should have approximately 3/8” – ½” (1.0 – 1.3cm) ease.  As mentioned above, these numbers are flexible based on previously stated variables.
Factors affecting Sleeve Fit:

1. Cap height
2. Cap width
3. Shape of the cap
4. Relationship of the front to the back of the cap
5. Cap ease
6. Shape of your shoulder and upper arm
7. Underarm/bicep circumference
8. Fabric choice (woven vs. knit)
9. Style of sleeve (tailored vs. casual)
10. One or two-piece sleeve
11. Sewing technique for setting in the sleeve

Of this short list, one of the most important factors is sleeve cap ease, which is the extra length the cap has that shapes the fabric to lift and fit up and around your shoulder joint.  Sleeve cap ease affects the cap height, width and shape of the cap.  It would be great if there were hard and fast rules about cap ease, but that is not the case…it is all variable!  It varies depending on the fabric choice and the intended profile.  Is the garment a camp shirt, tailored jacket, or somewhere in between?
This discussion will go on to deal with changing the sleeve cap shape and ease, but first another extremely important determining factor in the sleeve fit is your bicep circumference and the required ease for your arm girth.  This is actually the first, if not most important factor in sleeve fit.  If the sleeve doesn’t go around your arm comfortably (arm plus ease), then it won’t matter what is going on with the sleeve cap ease – it’s simply not going to fit or look decent.
The amount of bicep ease is once again variable and depends on its own factors, such as style or profile of sleeve and fabric choice.  A knit sleeve will need less circumference ease than a woven sleeve.  For the SFD bodice test, I usually suggest 1 ½” – 2” (3.8 – 5.1cm) bicep ease.  If your upper arm is particularly large and you already have to widen the sleeve substantially, try to keep to the minimum amount of ease.  But if the test garment feels too tight for comfortable movement, then you’ll need to add more ease.  The width of the sleeve at the underarm is always going to be the primary factor for fit.  The cap height, width and its subsequent ease will simply need to be adjusted as best as possible.  There is no magic bullet.  See Large Upper Arm Minor Tune-Up, page 18 #13 of the Dress Kit Instruction Book and/or video D.9.5 Large Upper Arm Alteration.
Sleeve Cap Shape and Ease

Let’s assume you’ve drawn your SFD bodice front, back and sleeve pattern. Keep in mind that many of you will have changed the shape of your armhole.  You may have ‘scooped’ the armhole shape more dramatically for your narrow upper chest or back blades width.   (Perhaps you would have watched video D.9.4 Refining the Fit: Dress/Shirt Armscye Modifying/Scooping the Armscye Curve.)  
Changing the sleeve cap ease depends on the length of the line.  A curved line going from point A to B is going to measure longer than a straight line going to and from the same points.  Whether you need to add or subtract cap ease, you can change the height of the cap, increase or decrease the shape of the cap curves or change the width of the bicep.  
As an example, if you need to decrease cap ease and you have a small bicep, consider decreasing the underarm points – bringing them in to a smaller number.  Even if you have a small bicep, you can always apply the principle of adding approximately 1 ½” – 2” (3.8 – 5.1cm) bicep ease and comparing to the master pattern.  But if you have a large upper arm/bicep, you likely won’t be reducing the width of the sleeve once you’ve established your correct circumference + ease, so that leaves the cap height and width (controlled by the curve of the cap) to make changes in sleeve cap ease.
How to change Cap Ease – 3 Alternatives:
1. Decrease/increase cap height
3. Decrease/increase bicep width
2. Decrease/increase cap width
The Pitch of the Sleeve

We’ve all seen sleeves that have a more or less diagonal fold coming from around the elbow and heading up toward the cap.  **Please note that this is going to happen on all one-piece sleeves to some degree.  That is because your arm does not hang down the side of your body in a perfectly straight line.  From the elbow, your forearm pitches forward.  
Many one-piece sleeves are basically straight.  Placing this straight piece of fabric on your slightly forward-pitched arm will cause the upward diagonal fold from the elbow up because that’s where your arm starts to bend.  Some one-piece sleeves do have a slight forward pitch below the elbow dart, as does the Sure-Fit Designs™ sleeve, but unless this pitch is rather dramatic, or you have a two-piece shaped sleeve, it really isn’t possible to totally remove this diagonal fold.  It’s simply part of the overall make-up of the one-piece sleeve.
For ease of simplicity, the SFD sleeve has a slight forward pitch with a 1” (2.5cm) wide fold up hem allowance.  If you would like to increase the forward pitch, follow these directions.  Click here.  As you will see in making this change, the hem will curve meaning it would need to be hemmed with a shaped facing.

In closing, this article offers a lot of information and food for thought on the topic of set-in sleeves.  My intention in offering this to you is not to overwhelm, but rather to give you facts that may pertain to you that will enhance your personalized sleeve fit.

Sleeve Facts: Sleeves & all their quirkiness!


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