Objective: Assemble the main structural seams of your capstone item into a sound, sellable core using the MC6650's stitch and feed controls.
The 'core' is the load-bearing skeleton of your product: the seams that give it shape and strength (side seams of a tote, body panels of a zip pouch, the main body of an apron). This is where hobby-quality and sale-quality diverge, so technique matters. Work in a logical order: join pieces that build the largest flat sub-assemblies first, then connect sub-assemblies, leaving openings for turning, closures, or linings as your pattern specifies. On the MC6650, set a straight stitch (stitch 1) at length 2.4-3.0mm for most cottons and canvas; drop to 2.0mm only for tight curves. Keep a consistent seam allowance by lining the fabric edge against the needle-plate guide lines (commonly 3/8" or 1/2"). Use the machine's needle-down function so pivots at corners stay crisp, and backstitch 3-4 stitches at the start and end of every seam, or use the lock-stitch button, so seams don't unravel under customer handling. Reinforce stress points — bag handle bases, pocket corners, strap joins — by stitching a small box-with-an-X or sewing over them twice. Press each seam as you go (press, don't drag the iron); an unpressed seam hides twists and bulk that will show in the finished product. The MC6650's even feed is helped by matching needle and thread to fabric (90/14 for canvas, all-purpose polyester thread) and reducing speed with the slider for thick intersections so the feed dogs don't stall.
Example: Say your signature item is a lined canvas tote. Core order: (1) sew the two outer body panels right-sides-together along both sides and the bottom, 1/2" seam, stitch length 3.0mm, backstitch each end. (2) Box the bottom corners: flatten each corner into a triangle so the side seam meets the bottom seam, measure 2" across, sew straight across, and backstitch — this creates the flat base. (3) Repeat identically for the lining but leave a 4" gap in the lining bottom seam for turning later. Press all seams open. You now have a structurally complete outer shell and lining core, ready for handles and finishing in Lesson 4.
Try it: Sew the main structural seams of your own capstone piece today. Set the MC6650 to straight stitch, choose a stitch length appropriate to your fabric, and engage needle-down. Join your largest sub-assemblies first, backstitch every seam start and end, reinforce at least one stress point with a box-X, and press each seam immediately after sewing. Stop once the core holds its intended 3-D shape but before adding closures, handles, or final edges. Lay the core flat and compare it to your pattern.