Tutorial 33. Calculation of petticoat gores and lining gores.
So, we can start the skirt when the dress bodice is ready: the drapery is made and fastening is made as well – zipper or lacing.
At this stage I should calculate and cut the lining and petticoat base. I developed the automatic calculation tables for this course, which help to get all numbers for cutting the skirt lining, petticoat and ruffles in no time.
As for the outer skirt, we will calculate and sew it by hand later. I will demonstrate everything on the mockup. Our task now is to prepare the internal construction, where the beautiful outer skirt will be put on.
First of all, I set the dress-form with the ready bodice at the level, which corresponds to the skirt length of my client.
The most important requirement to taking this measurement is following: the client should wear the same shoes, which she plans to wear this dress with. If you break this rule, it will complicate your work, lead to additional fabric consumption as you have to add extra fabric along the length while cutting as if the skirt is shorter even for 1-2 cm, it will be practically impossible to change its length.
The skirt length is taken as follows: a cord or elastic tape is placed on the client’s waist and a centimeter tape is placed under the cord or tape in the front center. The centimeter tape is in free hanging position and the contact point with the floor will show the length of the front skirt for your client.
The front length will be the starting point to set the dress-form to the desired height of your client. We will be guided by the dress-form when we take measurements from the ready-made skirts and a petticoat that are on the dress-form.
So, I determined that the front length of my client is 125 cm from the waist to the bottom. I have set this height on the dress-form. Now I can safely create our skirts without thinking about their length at all.
I measured the distance from the lining bottom to the floor on the dress-form, which is 2 cm shorter than the dress base and it was 90 cm. The top circumferences of the skirt and lining also comprise 90 cm.
I start calculating the lining skirt based on the front length of 90 cm and top circumference of 90 cm.
I open the sheet «Skirt» in the calculation table «calculation of the skirt along the bottom length” and enter the data for the ←calculations (red arrows) :
- top circumference - 90 cm;
- skirt length - 90 cm.
The next parameter to enter to the table is the bottom length or in other words, the desired bottom circumference of the lining skirt in this case.
I set this measurement at 250 cm and let me explain why.
I made the mockup of our dress, which, as you see in the photo, I always have it in front of me. Looking at the mockup, I see that the volume of the front skirt will be beautiful if its bottom is about the size of the stand on which the miniature dress-form stands. And if the skirt is also a little wider, relative to the stand, then it will just look great!
Apart from all advantages I mentioned earlier, the mockup allows us to see the future skirt in proportion to the dress. You don’t have to imagine anything as everything is visible!
I measure the circumference of this stand and it is 120 cm. This is the half-size, thus, the length of the outer skirt, as well as the lining skirt and petticoat should be about 250 cm.
I enter 250 cm as the desired bottom circumference into the table.
You have to remember all the time, that 250 cm is the bottom circumference for the skirt of 90 cm long from the edge of the dress base to the floor. This is the bottom circumference of the skirt, when it is on the floor. When we will make shorter the petticoat for comfortable movements and the lining according to the length of the petticoat, the internal circumference of the lining and petticoat will be less. Their bottom will be in some distance from the floor, thus the bottom circumferences will be less, however, the flare of the outer skirt, petticoat and lining skirt will be the same.
We will see it all during the calculation in our table.
The main calculation parameter which we need to receive is the value of a sector angle – the alpha angle. The table showed that this angle is 102 degrees.
What the alpha angle is and why it is so important I have explained in detail in the course “Dressmaker’s treasury. Wedding dresses and petticoats”. I try to explain briefly for those who are not familiar with this course.
It is well known that the flare of any skirt that we sew is either a full circle or some part of a circle. For example, a circle skirt is a full circle, respectively, the alpha angle of this skirt is 360 degrees. And the flare of a ¾ circle skirt has the angle alpha of 270 degrees. Both in the circle and in its part, referred to a sector, we can find the length of the outer line using the simplest formulas, which will be the bottom circumference or the hem length if we know the alpha angle.
We have the opposite task: we know the bottom circumference or the sector outer length, which comprises 250 cm and we need to determine the alpha angle, which show how much flare we have. The automatic table calculates 102 degrees. We will need this number further, so that the program can divide the skirt into sectors and calculate all their measurements. We just need to cut those skirt parts and sew them.
The most important thing is the program uses the same alpha angle of 102 degrees despite the various lengths of the main skirt, lining skirt and petticoat. Only in this case all skirts of our dress will have similar flare and different length.
The theoretical information will become clear during our further calculations.
Thus, we will use the alpha angle for calculation of our skirts. I draw schematically the lining and the petticoat. And now I will gradually fill this scheme with numbers. And, most importantly, these numbers I will use for cutting and sewing the petticoat and lining.
Go to the table to the sheet “calculation of ruffles for the petticoat”. Our task is to find the length of the base (petticoat) or the length of the petticoat, which we will sew ruffles on.
We set the same parameters (red arrows in the photo):
- top circumference of the petticoat base - 90 cm. I took this measurement along the bottom of the dress base.
- petticoat length with ruffles - 90 cm.
- alpha angle, which we determined - 102 degrees.
The calculation shows the length of the petticoat base should be 79 cm (blue arrow in the photo).
Please note that 79 cm is the length of the petticoat base. When we attach all ruffles to it, the length of the petticoat will be 90 cm. The length of the ruffles will be also calculated. The base should be shorter than the skirt and we actually got that: the petticoat is shorter for 11 cm than the outer skirt.
I write down the numbers on the petticoat scheme.
Let’s continue to work with the lining skirt. When we insert the lining in the petticoat, the lining should be at least for 2 cm longer than the petticoat. At the same time the lining should not reach the floor i.e. it should be shorter than the ready dress.
If you look at the bodice of our dress, you will notice that the outer layer, where the petticoat will be attached, is 2 cm longer than the lining, where the lining skirt will be attached.
We have defined the petticoat length of 79 cm.
Based on our considerations, in order to find the length of the lining skirt, I must compensate 2 cm for the difference in the height of the sewing of the petticoat and the lining and take into account that the lining should be 2 cm longer than the petticoat. Therefore, to calculate the length of the lining skirt I have to add 4 cm to the length of the petticoat.
Therefore, the length of the lining skirt should be 83 cm. The top circumference of the lining skirt is 90 cm. I do not know yet the bottom circumference of the lining skirt or the length of its hem: this value will be automatically calculated based on the alpha angle of 102 degrees and the skirt length of 83 cm.
Now, when we know the length of the lining skirt, the automatic program can divide this skirt into gores for cutting and calculate their sizes.
To do this, we go to the “gores” sheet in the table and set the necessary parameters.
I set the parameters for the lining skirt (red arrows):
- top circumference - 90 cm;
- front length - 83 cm;
- back seam length – 83 cm too, as we don’t have any extensions on the lining.
- alpha angle – 102 degrees;
- gathering coefficient for the top – 1, as there is no need to gather in the sewing area.
- I suggest choosing 6 gores. There will be 3 front and 3 back gores.
All 6 gores are similar.
I enter all initial data and receive immediately the full calculation of a gore with a side length of 83 cm:
- top length - 15 cm;
- bottom length - 40 cm;
- arc along the top center – 0.6 cm;
- and arc along the bottom center – 1.5 cm.
I write down the sizes of a gore on the drafting scheme.
How do we cut a gore?
As I have already said, all gores are are similar. The only thing is you can make a middle seam on the back, i.e. the middle back gore is divided in half. But this will depend solely on the layout of the patterns on the fabric, if you want to make it more economical. From technological point of view, we absolutely do not need this seam, because the place to sew the lining skirt to the waist has nothing to do with it, there is no fastener there, and therefore, it is not necessary to divide the back of the skirt into 2 parts.
We know all sizes of the gores. You need to consider the top and bottom arcs, so when you sew it there will be rounded lines, but not the broken straight sections.
Therefore, we have calculated the lining skirt and got the whole scheme for its cutting. We make the gore pattern based on these data and cut it from the lining fabric.
Now let’s divide and calculate the gores for the petticoat with hoops.
We use the same table and make one change only:
- skirt length along the front and the back seam and it is the petticoat length of 79 cm in our case.
We get a layout for the petticoat gores with a side length of 79 cm: it is absolutely natural that the top length of the gore and its arc completely coincide with the top and the arc of the lining gore, and comprise 15 cm and 0.6 cm. However, the bottom length of the petticoat gore decreased to 38 cm. This is also easily explained by the fact that if the length of the petticoat base is shorter by 4 cm than the lining skirt, the length of its hem will also be less. The bottom arc of the petticoat gore slightly decreased to 1.4 cm.
I write down the sizes of the gore to the layout scheme of the petticoat. We can confidently cut the gores of the petticoat and sew them.