SINGER W431 - Manual (Page 32)

BUTTONHOLES
Various fabrics require various methods of sewing
buttonholes. Two different methods are given below,
with suggested uses. If you are in doubt as to which
method is best for your fabric, test the methods in
question and choose the best according to the finished
appearance.
PREPARATION
For the best results, a good quality mercerized cotton
thread should be used. Polyester threads often result in
puckered or heavy unattractive buttonholes. The finer
your fabric is, the finer your cotton thread should be.
An interfacing should be used under the buttonholes to
give body, to strengthen, and to help them withstand
wear.
To establish the correct length of the buttonhole, add
the length of the button (A), plus the thickness of the
button (B), plus 1/8 inch for the bartacks. The length
may be marked on the garment with a basting stitch,
tailor's chalk, or an invisible cellophane tape, as shown.
Horizontal buttonholes should extend 1/8 inch beyond
the centerline of the garment. Vertical buttonholes are
placed so that the cutting space of the buttonhole is
directly on the center line.
Always make a practice buttonhole on a scrap of the
garment fabric before making any buttonholes on your
garment. On your test sample, duplicate the thicknesses
found in the garment and be sure to include the
interfacing. The test sample should help determine the
length needed for the button to pass through the hole
easily, as well as the stitch length needed for the
particular fabric. As with the satin stitch, the stitches
should be close together, but not so close that they pile
up. Be sure to use the buttonhole foot.