Truing Armhole Dart

Hi wonderful folks,

Was wondering if I could get some help with truing an armhole dart on a slight curve. I went through some older topics, but couldn’t find one the helped directly.

This is the armhole dart I am attempting to true, from A4-K-A4_a1.

On paper I would just fold A4 and A4_a1 together and then cut along the curve. Once I unfold the paper, I would have a perfectly trued dart. I imagine it should look something like this:

truedart_armhole.pdf (83.6 KB)

How do I accomplish this?

Thank you so much!


Sorry I can’t provide a screenshot to illustrate- I’m not at my laptop.

First use the “Point along bisector” tool to create a bisector of the angle between A4_A1, K, and A4. Choose points A4_A1, K, and A4 in that order, and use the length for the bisector to be Line_A4_K or Line_A4_ A1_K. I assume they should be equal, if not I’d chose the longer one. It will create a new point… let’s say it’s A5. The bisector would represent your fold line. Now you can create a line from A4 to A5, and A5 to A4_A1. To make a pattern piece you don’t actually need the 2 lines, but they make it clearer in the draft block what the piece outline should look like. Technically, you would create 2 curves which would be closer to folding and clipping with scissors, but the difference is so slight, it’s just easier to use the lines.



What I’ve done here is…

I’ve rotated the armhole curve with the other points because this gives the quide to the amount of fabric needed to close the dart securely.

Then I created the bisector point that @Douglas described.

Then using the Intersection Point of Curve and Axis (CA) tool, I intersected the curve from from the new point A41 (A5 per Douglas) at the angle of line A26_A41.


I just put in a line to connect A44 to x14 but you could flip the armhole curve, if you wish or draw in a new curve for that small section, if you wish.

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Yeah… actually depending on the width of the dart, I would tend to true the dart up in the sense that the current True Dart tool works. That is, to lengthen the dart so that the legs of the dart and the armhole seam create a 180 degs across the seam so as to not create a Vee across the seam. If it’s small enough - like a 3/4" dart on the back of (mens) pants - it’s not really neccessary to raise to true the dart. Also the True Dart tool works OK for a skirt or pant waist, I don’t think it would well in this example.

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Hi, did you find my sollution I posted here?

I did this for a dart on a curved waist seam, but you could do this for an armhole too. This is actualy like the paper method.

in short:

  • first you copy the needed points - I do this to keep the original clean
  • fold the pieces together.
  • draw the curve
  • split the curve a the dart
  • recreate the curved pieces and dartlegs in the original
  • clean up (hide) the copied points

Good luck


Hi Douglas,

Thank you! I gathered that I needed to use the bisector tool to create A5, but had trouble figuring out the length of A5 so the dart would fold perfectly as it would have on paper. A5 would be quite a bit longer than the other two dart lines…

I am going through everyone’s solutions multiple times to see if I can figure it out…

Thank you again!


Hi Grace,

Thank you for the solution of rotating the armhole curve with the other points, I think this helps me determine how long A5 needs to be for the dart to fold properly. :slight_smile:

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@SewingEngineer Yes I downloaded your guide! I will be going through it more thoroughly and put it to practice. Thank you. :slight_smile: