Abbye is back and better than ever

A couple of days ago I was chagrined to report that I had got my maths wrong on the sleeve cap of Abbye.
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Well I’m now happy to say an update has gone out to all customers with the corrected (and re-TE’d) sleeve cap, and the pattern has been reactivated.

Although I was most ashamed to have to fix an erratum, I am nonetheless proud of the fact that I got the corrected pattern re-released less than 24 hrs later.

I am very grateful to the customer who found and reported the error, and I was very happy to refund the price of the pattern to her. She is going to unravel the tops of the sleeves and redo, and I can’t wait to see the finished cardi.

If you find an error in one of my patterns, please let me know so I can fix it for you and any other knitters who have the pattern. As they say in business, if you got a problem with my products, tell me, if you like my products, tell everyone else!

Happy knitting,
X
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Calculate Sleeve Cap Height Given Top Arm Circumference and Armscye Perimeter

I previously explained why I think the Sleeve Cap can be described by an oval. Basically, a sleeve can be thought of as a cone which intersects the “plane” of the sweater/cardigan.

This produces an ellipse.

The perimeter of the ellipse is at least the same as the perimeter of the matching armscye on the body of the garment. If the perimeter of the ellipse is smaller than the armscye, it won’t “fit” – used in cap sleeves only. If the perimeter of the ellipse is larger than the armscye, you can ease the excess all around, or into the top to produce a gather. In any event, the armscye perimeter can be calculated from the garment body measurements.

You also will have a measurement for top arm circumference. The top arm circumference for a woman of average height is around

Bust 32 36 40 44 48
Top Arm Circumf. 10.5 11.5 13 14 15.5

Don’t forget to add ease! This is an unclothed measurement.

You can see from the diagram below, that the top arm circumference, i.e. the widest part of the sleeve, is equivalent to the width of two ellipses (0.5 + 1 + 0.5 ellipse widths). Hence, the horizontal radius of the sleeve cap ellipse is a quarter of the top arm circumference.

The sleeve cap height is twice the vertical radius of the ellipse, i.e. the same as the height of one ellipse.

If you plug the values for perimeter and horizontal radius into Ramanujan’s Approximation for the perimeter of an ellipse, you can get a good-enough value for the sleeve cap height.

The sleeve cap height is twice the value for c, the vertical radius of the ellipse, approximated by

Where p is the armscye perimeter / pi

And w is the top arm circumference / 4

The approximation above is essentially Ramanujan’s Approximation expressed in terms of one of the radii.