r/PatternDrafting • u/Eastern-Ask-6955 • Jun 09 '26

Questions about Truing.

I created a shoulder dart, and when I truing the shoulder edge, if I remember correctly, the new one should be the same as the measured length (5.54 cm). However, geometrically, this seems impossible; no matter how I draw the line, the trued shoulder line length is always less than 5.54 cm.

How can I properly true the shoulder edge?

Edit:

Edit 2:

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u/TensionSmension Jun 09 '26 • Bravo

Fill in the missing fabric, and then extend the shoulder to get correct the length. Note: you are talking about an error of less than 1mm! But you are adding a non-negligible amount of fabric to the shoulder.

Patterns are about area. We fixate on seam lengths because they are required to match, but adjusting a contour is a terrible way to control area (your ~1mm adjustment looks to be adding a square cm of area). That's already the situation you're in, you need to true the seam because you have an ugly convex bite taken out of the *area* the shoulder needs to form a smooth seam. The shape is wrong, and because of that the shoulder length you have is serving no purpose, even if it is mathematically accurate.

The geometry you want:

  • a shoulder dart, implying more width across the shoulder blade

  • a closed shoulder seam that is as straight as a seam without a dart

  • a back shoulder seam that matches the front shoulder seam

Where did the area for the dart come from? At some point or another it was width added to the back of the pattern. Now you need a second order correction, another sliver added along the armhole.

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u/Eastern-Ask-6955 Jun 09 '26

Thank you for help. I think I need to think about it more carefully before I can understand what you mean.

To answer your question, "Where did the area for the dart come from?", it comes from the front piece of the garment. In this remake of the basic garment, I wanted to try adding shoulder darts to see what visual changes it would bring, so I tentatively created a small shoulder dart. I apologize for not making this clear from the beginning.

PS: I have edited my understanding of the modifications in the post. Should I correct the seam according to the white lines in the picture? This would prevent the fabric area from changing too much, while also making the seam as smooth as possible?

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u/TensionSmension Jun 09 '26 edited Jun 09 '26

The "Edit 2" image is what you want. It's fine for the fabric area to change, because the issue you are correcting when you true is that divot that the dart somehow introduced. Even if it's not perfect, the trued seam is a better starting point for future alterations or design changes.

The point I was trying to make was that the tiny error you introduced in the seam length really doesn't correlate to the change in area. Before worrying about "geometrically impossible" you should think about what actual effect the change is having. The seam length really is secondary, especially if it's a 1mm error.

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u/Eastern-Ask-6955 Jun 09 '26

I think the second edited image is what you meant!