Objective: Master three intermediate controls on the Janome MC6650 — needle position, needle-down pivoting with the knee lifter, and controlled topstitching — so your finished items look professional enough to sell.
Selling-quality sewing depends less on speed than on consistency, and the MC6650 has features built for exactly that. First, accurate seam allowances: instead of trusting the printed plate line, move the needle itself. Select the straight stitch, then use the width adjustment to shift the needle left or right in small increments; combined with the edge of your presser foot or the magnetic/screw-on seam guide, this lets you hit a repeatable 1/4" or 5/8" every time. Second, clean corners: turn on the needle-down setting (the up/down button or the auto needle-down preference) so the machine always stops with the needle buried in the fabric. That anchor point lets you lift the presser foot, pivot the fabric exactly 90 degrees, drop the foot, and continue — with no shift or gap in the stitch line. The knee lifter (the lever that plugs into the front of the machine) raises and lowers the presser foot with your knee, keeping both hands on the fabric during the pivot. Third, topstitching that doesn't pucker: lengthen the stitch to about 3.0-3.5mm, reduce speed using the speed-control slider, and use a walking foot or edge-joining foot to feed top and bottom layers evenly. Sew slowly and guide — don't pull — the fabric.
Example: Make a mitred square patch for a zip pouch front. Select straight stitch, shift the needle right until the fabric edge rides along the inner edge of the foot for a true 1/4" seam. Turn on needle-down. Sew the first side; when you reach the corner mark, the machine stops needle-down automatically. Nudge the knee lifter to raise the foot, pivot the fabric 90 degrees around the needle, lower the foot with your knee, and continue. Repeat at all four corners. Then switch to a 3.2mm stitch length, drop your speed to about half, fit the walking foot, and topstitch 1/8" from each seam — the result is a crisp, even square with sharp corners and flat, pucker-free topstitching.
Try it: Cut two 6" fabric squares. Using needle-position adjustment, sew around three sides with an accurate 1/4" seam, using needle-down and the knee lifter to pivot at each corner. Turn the piece right side out, press, then topstitch 1/8" from the edge at 3.2mm stitch length and half speed. Inspect your corners for sharpness and your topstitch line for puckering; re-sew if needed until both are clean.