DARTS - Part 4 - How to Increase or Decrease Projection in a Darted Cup
Check out the entire Darts in Lingerie Series:
This is a 4 part series that walks you through everything from how to sew giant curved darts in bras and lingerie but also how to adjust patterns and some basic understanding about the volume and (cone) shape implications specific to bra cups.
Part 1 - How to Sew Giant Curved Darts
Part 2 - Inner Fullness Adjustments for Darted Cups (Quick & Dirty)
Part 3 - Narrow Root Adjustment of a Darted Cup (Mysa Only)
Part 4 - How to Increase or Decrease Projection in a Darted Cup
This last section of the Darts in Lingerie Series includes a primer on the Volume of a Cone as its key to understanding how to increase or decrease the projection (and thus volume!) of a darted bra cup such as our Mysa Bralette and Lamina Underwired . Some of this will sound familiar due to various paper experiments with paper cones in Grammer School (AKA Elementary or Primary School) but when viewed through the lens of lingerie pattern drafting and alteration, can be quite eye opening.
Cone Volume Basics
Bra cups (and breasts) are essentially cone shaped - at least that’s what the industry generally designs for - but we’ll chat more about that another day. Take a look at the image on the lower right hand corner for Dr Shin’s drafting book (My review of the book HERE). Although much simplified, the cone shape does give us some numbers to play with and a general starting point.
Some of you may recall primary school experiments with circular sheets of paper and making a cone shape by cutting a slit to the center, overlapping the corners and taping the ends together to form a hat, cup or other craft. The more you overlapped, the taller and skinnier your hat/cup became.
What does this have to do with bra making and alterations? Check out the similarities between these two images. The bottom, say 2/3 of the illustration, has quite a few similarities and some differences to a typical darted bra cup. Lets start with the commonalities.
3D Paper Cone Shape
Typical 34B Darted Cup Shape
COMMONALITIES
Same HH and BCD - Less Projection, Less Volume
Same HH and BCD - More Projection, More Volume
These screen shots from Geogebra illustrate the concept nicely. The left side of these images shows the “flat paper pattern” while the right side of the images is the 3D version taped together. Take a look at the numbers but pay particular attention to the Volume and Height.
Slant Height = BCD (Bottom Cup Depth)
Slant Height x 2 = HH (Horizontal Hemisphere)
Height = Cup Projection
Volume = Cup volume
Base Radius = Underwire width (opening)
The Slant Height remained the same in both examples. That means the BCD (10cm) and HH (20cm) are unchanged despite the increase in volume AND height.
In short, the “wedge removed” or negative space directly relates to the volume the cone or cup is able to hold. Laurie of VanJonsson Design mentions this concept as well.`
Check out this Link where you can enter the different measurements and print out to conduct your own experiments!
DIFFERENCES
While there are some obvious differences between the 3D Paper Cone and 3D Fabric Cup, such as the lack of a underwire constraint and less surface area of a demi cup vs full coverage, there are some other less visible differences as well.
CUP STYLE
In general, a container that is shorter on one side means the container cannot hold as much liquid volume. Since breasts are a Non-Newtonian Fluid AND attached to a stable surface on one side (ie, torso), this is not the case with bras. We can have quite a bit of breast tissue sit on top of a well fitting bra cup, much like a towering swirl of whipped cream on a tiny ice cream cone.
FABRIC TYPE
Fabric type - density, weight and stretch also play a role in cup volume. The most obvious one is the difference between a stretch and non stretch cup. Less obvious is the rebound ability of stretch fabric or the need for a curved dart in non-stretch fabrics. More info on stretchy bralette fabrics here.
UNDERWIRE CONSTRAINT
Due to the popularity of cup styles that are NOT full coverage (demi, half, quarter, plunge cups, etc) and the fluidity of fabric, bra cup shape can deviate from the original design. The most common way this occurs is using a wire and/or wireline that is wider than intended. A perfectly fitting bra cup will look/feel misshapen due to wires that are too large/wide as the wire pulls the cup further back at the underarm reducing cup projection. Keeping in mind that a minimizer bra (a bra designed to FLATTEN the breast) starts with a wire that is larger/wider than typical, this may result in an inadvertent minimizing look.
HOW TO INCREASE/DECREASE PROJECTION IN A DARTED CUP
Now that we’ve sorted the why, lets move on to the how.
INCREASE PROJECTION IN DARTED CUP
Increase the negative space of the cup by making the dart wider.
Begin by drawing a straight line from the bust point to the underarm. Slash and hinge at the bust point.
Manipulate the hinge so there is some overlap at the underarm and opens up the main dart.
Redraw the underarm curve tapering to nothing at the corners.
Add seam allowances back on.
In cases of large increase, you may need to shift the strap attachment point toward the front a bit to keep the proportion.
DECREASE PROJECTION IN DARTED CUP
Decrease the negative space of the cup by making the dart narrower
Begin by drawing a straight line from the bust point to the underarm. Slash and hinge at the bust point.
Manipulate the hinge so there is a gap at the underarm and reduces the width of the main dart.
Redraw the underarm curve tapering to nothing at the corners.
You may also want to decrease the curvature of the dart leg seams**
Add seam allowances back on.
In cases of large decrease, you may need to shift the strap attachment point toward the arm a bit to keep the proportion.