Hello everyone,

I am very happy to see you once again. At the moment, I'm trying to understand as precisely as possible all the elements of jacket pattern-making. Because I think it's much harder and more time-consuming to get it right if you don't understand what you're doing.

I haven't found any good books that explain everything I'd like to know. Cutting books are often pithy, reduced to mathematical formulas and quick instructions, without ever explaining why they do what they do.

Nevertheless, I've scoured the internet for obscure and fascinating forums and have found almost all the answers to my questions.

However, I still have 2. One on the question of shoulder slopes and one on the question of the shape of the seam between the front and the side body, or on a front without a side body, on the side dart.

I. Determining the front and back shoulder slope.

There have been many ways of determining shoulder slopes throughout the history of cutting. In books from the early 20th century, the proportional method gives a shoulder front and back seam with very different angles and results in a seam positioned very strangely for modern standards.

I don't know when this method was abandoned, but it seems to me that today we try to position the shoulder seam much more evenly between front and back pannels.

In a previous reply on this forum I read that Reza indicated that a good solution for working out the best possible shoulder angle is to measure the angle with an app on your phone and transfer this angle to the pattern (photo 1).

Here's my question at last! Once you've determined the front shoulder angle and applied the desired length, how do you determine the back shoulder seam?

My idea for this question is as follows (photo 2): The angle measured on the telephone is angle (a). Once you've determined point G, draw a line (red dotted line) perpendicular to the breast line (bottle-green dotted line). And on this line we draw the back shoulder seam so that the final length (B-D) (length determined in advance) arrives on this red line.

Is this a correct cutting idea from your point of view?

II. The shape of the strangest seam on earth ! (side seam).

I'm wondering about the angle of this seam, positioned roughly on the side of the jacket. I'm showing a pattern without a side body because it makes my question clearer, but as far as I know, the side body is always cut in the heritage of this "angled" way of positioning the side seam, so my question also applies to a jacket pattern with a side body.

As far as I know, the angled seam appeared around 1930. And it became more pronounced over time, reaching its current angle (perhaps definitive, I don't know if history is still moving on this) in the 40s and even more so after the war. Earlier jackets have seamless patterns in this position (jackets didn't fit at the beginning of the 20th century because they were sportswear) or sometimes seams perpendicular to the chest line (which are more like darts because there was no separate side body at the time, apart from military uniforms). I show this type of cut in photo 4 in blue.

However, in modern cut books (the precise style I use comes from a 1974 book called "Fundamentals of men's fashion design; a guide to tailored clothes" by Kawashima, Masaaki, available on internet archive), this seam is angled (photo 5 in purple). I've never understood why this seam was cut at an angle. From my point of view, the human body doesn't find an angle here, so I don't see how this 'angled' seam fits in with the human anatomy. However, everyone seems to have been doing this for the last 80 years and I don't think I've understood the universe any better than the rest of the world, so I guess I'm missing something and if you have an explanation for what I'm missing I'd be very happy to hear it.

I hope you find the answers to my questions, and above all that they were understandable!

Good day to you all!