Check with your insurance agent (and be sure to have receipts proving initial cost), but most single high-value items do require riders, especially if you want full replacement coverage (vs. actual cash value, which is going to be the depreciated value as determined by the insurance company).
If you do any sewing for compensation whatsoever, including making craft items to sell at shows, you'll likely need business insurance to cover the machines. Once an item gets used to make things you sell, it's no longer considered a personal item and typically won't be covered by your homeowners' insurance.