This diagram is also made for illustration only, for it would be too complicated for practical cutting. It is made for the purpose of showing the correct position of the back and sidepiece for cutting a sack coat without changing any balance in the armhole. The sidepiece is so placed that it will form a spring at the side of the hip, and the back and sidepieces are lapped over on top enough to balance one seam, leaving the sack as a three seamed garment.
The top of the back skirt and bottom of the sidepiece lap over, and which lap represents the extra length that the frock coat requires while passing closer to the hollow of the body. On the sack coat the spring over the hips is not used, nor is the larger frock coat gore behind, but between the two the sack seam is cut with a gore of about 1½ numbers at the hollow of the waist.
In placing the sidepiece in position, as in Dia. [III], the back part of the sidepiece on the shoulder blade falls backward and enlarges the square ½, and for this reason the three-seamed sack coat has a square of 18, or the same as a five-seamed frock.
In turning the sidepiece down into the waist, the top of the sidepiece will fall down behind and form the spring between it and the skirt, and consequently the whole frock coat back shortens on top, or from line 9 upward; and for the further reason that the sack coat back is the wider, the height of a sack back appears still shorter, as seen in Dia. [III] and [VIII], and is 13½. For further explanation as to why the back of a sack is shorter than that of a frock, see article on “[Narrow and Broad Backs].”
All foreparts in Dia. [I], [II] and [III] are in the same position, and all changes are made on the sidepieces and backs. Dia. [III] produces the closer-fitting skirt for a cut-a-way. All skirts are alike over the back, because all coats must fit the same over that portion of the body, but fronts of cut-a-ways must be closer than those of double-breasted straight coats. The lap of the top of the front of the skirt and bottom of the front of the forepart are reduced from the sidepiece forward, which takes away all surplus flow of the skirt. The gore in the fore-part is simply turned forward on a cut-a-way, while on a “Prince Albert” it stops at the waist seam.
The swing of the sidepiece in Dia. [III] is made at line 9 over the forepart and on the square of 20½. The break is made there, and the calculation is made from that point; and it is for this reason that an opening is made above line 9, which is about ⅜ at the height of the sack coat side seam, and is cut away on a frock coat, as a small gore, if the garment is cut in this position. But in a three-seamed sack coat the swing must be considered further back, or at the seam, consequently the opening is at the top of the sack coat side seam, which is cut out as a small gore between back and front and above line 11¼, or else the back armhole will be too wide, and show too much sleeve there. This gore may be made ¼ to ⅜ of a number, but which is obliterated when the sidepiece is turned so as to come in the position as shown in Dia. [VIII-a].
After the cut for Dia. [III] had been made, I came to the conclusion that the opening of the frock coat sidepiece and forepart toward the armhole, could just as well be balanced in a sack, by cutting it as a five-seamer, and by making back and forepart even above line 11¼, and this was one reason why Dia. [VIII B] was added.
Dia. III