Industrial sewing explained for upholsterers. Most of what is written about these machines is aimed at sailmakers, leatherworkers or garment factories — this is the same ground from an upholstery bench.
Thread
Bonded nylon or polyester, Tex sizes and the three numbering systems, which thread for which job, and the twist question.
Needles
Needle size by thread size, needle systems, round and leather points, and why a blunt needle causes skipped stitches.
Thread & needle selector
Three questions and you get the thread, size, needle, point and stitch length — with the reasoning for each.
Machines
Drop, needle, walking foot and compound feed; flat, cylinder, post and long arm beds. What to buy, and what you would rarely use.
Troubleshooting
Skipped stitches, thread breaking, puckering, tension and feed problems — in the order worth checking.
Setup & parts
Servo against clutch motors, speed reducers, presser feet, and the order to set tension in.
Where to start. If something is going wrong at the machine, it is thread or needle far more often than tension. The two guides above answer most of it, and the pairing between them answers most of the rest.
Six pages, and the section is complete.