what you'll need:
1 T shirt
pair of shears
serger (a sewing machine with a step zigzag will also do, but is not shown here)
a tape measure
let's get started
Step 1: Create the Pattern
the height of the hat should be more or less fixed. one can see, faintly, a fold line drawn on the pattern here, at about 2 1/4 inch from the bottom line. the lip of the hat will be folded inwards.
you can be creative and add more 'spikes' or make a 'mohawk' hat as well from this basic pattern.
* using the time-worn rule that the cervix has to be 10 cm dilated, using 2.5 cm/inch, and assuming my child was just born (more or less true), we can back out a value of pi to 1 significant digit.
Step 2: Prepare the T Shirt
next, turn the shirt inside out, as shown. this is not necessary if the two sides are the same, of course.
Step 3: Pin and Cut
place the pins parallel to the edge, and cut through both layers. you will note that I have cut a bit wider than the pattern here: I will check the size on the head, then cut down even more later if necessary. remember: it's easier to cut away more later than to add more later.
remove the pattern. keep the 2 pieces next to each other, but do not pin them.
Step 4: Serge the Outside Seam
this here is my serger, which I got on eBay years ago. sergers are almost as fussy as newborns. once you have them dialed in and working, they're great, but they will turn on you in a heartbeat. the main feature here is the cutting blade, which isn't terribly visible in these pictures. it does not like pins, but it likes fingers! take care.
It is easiest to make 3 passes: one on each of the outside sides, then the 'V' in the middle. you need not cut the serged thread ends.
try the hat on the child, still inside out. if it is too big, you can serge the sides down smaller (yay, cutting blade.) if it is too small, throw it away and go back to step 2. sorry.
Step 5: Create the Lip
first, with the hat inside out still, fold the lip back (again, this is about 2 1/4 inch or so).
then push the hat back right side out, folding at the line of the lip. from a cutaway view, it would look something like an 'S', but with a long tail. you are going to attach the loose top line of the 'S', which is the raw edge of the material (the edge which has not been serged) to the 2 layers at the curved bottom right part of the 'S'. pin the layers together; the pins should be perpendicular to the fold line.
now serge along the inside of the hat. NOTE: remove the pins before they hit the cutting blade. depending on your serger, you may booger your blade, or cause 2 half pins to go flying around the room. also, you probably don't want to be cutting away material with the cutting blade anyway. if possible, fold the cutting blade up for this operation, or keep the hat just to the left of the cutting blade.
after a full revolution around the lip, pull away, serge a few inches, cut the serged tail thread, and tie it off.