If, like me, you’ve never met a pair of jeans that don’t need to be shortened, thus requiring a new hem, then you have struggled with breaking needles when you try to sew across the seams (unless you’re Captain OCD, who takes the minimalist approach), especially this kind, flat-felled seams:
I worked with a guy whose wife hemmed his jeans for him. Instead of cutting them off and using a sewing machine, she turned up the legs, existing hem and all, and hand-stitched the new hem. Which resulted in a bunched-up, uneven mess varying from three to four inches above the bottom of his pants with erratic and inconsistently-sized stitches visible from the outside. Because she then ironed the jeans to achieve that all-important center crease, the folds on the inside of the legs, results of the subpar hemming, were even more visible. Don’t let this happen to you.
You want your jeans to look stock, so in most cases you must use a sewing machine. First, buy yourself some heavy-duty thread in the appropriate color, which means the same color as the topstitching on your jeans or the color of the original hem stitching and not the same color as your jeans. The thread is called variations of heavy, topstitching, buttonhole twist, etc. Then buy yourself a gross of regular needles or one needle manufactured especially for the heavy-duty demands of sewing thick denim.
Here’s the trick: After you’ve cut off the existing hems (don’t lazy-out on this step), ironed the raw edges under, and pinned them to the appropriate length, grab a hammer and take it and your jeans to a hard surface. Now, whack the seams a few times to break down the fibers and you’ll be able to sew through with relative ease with no broken needles or missed stitches. Depending on the fabric and the construction of the seams, you may need to go slow (very slow) and help the needle through by turning the wheel with your hand. Sewing through full-speed-ahead is what breaks the needles when they come upon a particularly dense section of fabric.
As you can see below, the color of the stitching on the new hem matches the original stitching.
After a few washings and wearings the new hem will look as used as the original hem (that’s how they came from the store). Whether you want your jeans to look like someone else wore them to muck out the barn before you bought them is a discussion for another day, one we can have while we’re sitting on the porch yelling at the neighbor kids: “You call that music?”