Adapting a pattern to the chest: princess seams and straps

Before modifying a pattern at the chest level, it is advisable to refer to the article “The basics of a chest transformation”.
The technique explained in this tutorial allows you to enlarge the front pattern so that the garment fits perfectly at the chest. Depending on the structure of the pattern, the modification will not be done in the same way. Here we will see how to enlarge a bodice with a princess seam or strap.  If the bodice needs to be reduced instead of enlarged, the technique will be the same. Instead of spreading the lines apart, they will need to be overlapped.

Basic material to perform a transformation
To transform a pattern, it is advisable to have:

• Adhesive tape

• A parrot rule

• A square

• A graduated ruler

• A support sheet

• A pair of paper scissors

• A fine-tipped pencil/criterion

Definitions

Let's first start by defining the following terms.
Princess cut : bodice with a seam starting at the armhole, continuing along the bustline and ending at the bottom.
Example pattern: the Tsar coat.
Strapless cutout : bodice with a seam starting from the shoulder, continuing along the tip of the bust and ending at the bottom.
Example of a pattern: the Maïa blouse dress.

In both cases, the bodice does not have a visible bust dart.

Front side modifications

The example below is for a pattern with a strap cutout. The dart (not visible) is placed at the shoulder.

Construction of transformation lines

The most significant modification is made to the front side piece. A slight adaptation will also need to be made to the middle front piece.

• Check that a mark is placed at the apex (breast tip), that is to say on the most rounded part of the piece. This point will serve as a basis for the transformation of the pattern.

• Starting from this point, draw 3 axes on the pattern:

  - Draw a line A towards the side, near the underside of the sleeve.

  - Draw a biased line B ending in the armhole. Avoid the lower part, because the line is very curved.

  - Draw a parallel line C along the straight grain all the way down.

  - Draw a line D perpendicular to the straight grain, a few centimeters from the bottom. This axis connects the princess cut/strap and line C.

Key point: Use a sheet of paper as a support, because depending on the model, the split piece may have very small elements.

Transformation of the boss

The transformation is identical to a bodice with a classic dart. Refer to the article “Adapting a pattern to the chest: the classic dart”.

• Cut on lines A, B and C stopping 2-3 mm before the armhole and the apex point.

• Attach the part that does not require a pivot to a sheet.

• Separate the different parts of the necessary measurement. Line C must always remain parallel to the straight grain.

• Then cut line D and adjust the location of this small part so that it aligns with the bottom.

  

• To absorb the existing clamp following the pivot of the parts, draw an axis in the extension of the lower line of the clamp, until meeting point x , on the other side of the gap.

• Cut on the line to split the princess/strap cut line in 2.

• Close the clamp, pivoting the entire upper part of the part. A new gap is formed at point x . This is the principle of the clamp pivot.

• The spacing measurement obtained towards the apex point (tip of the breast) is very minimal and will be absorbed when fitting with the middle front piece.

  

Mid-Front Modifications

• Draw an axis perpendicular to the straight grain on the bottom of the middle front piece.

• Cut on the line and separate the 2 parts of the missing value so that the piece has the same height as the front side piece.

  

Adjusting the parts

At this point, we observe that the bottom of the front has widened proportionally to the measurement added to the chest.

• Subtract the extra measurement on the side, then retrace the line.
• Also trace the rounding of the princess/strap cutout.

After all these modifications, it is advisable to carry out a test in a canvas before starting to make your garment.

Another scenario

When the clamp is rotated at the waist, the transformation technique remains the same as before. Only, the line C parallel to the straight grain will pass outside the part, almost in the center of the clamp. It is therefore necessary to remember to fix the part on a paper support before starting the modifications.