Perpetual pirn for a sewing machine - with embedded point to avoid the need to reload the pirn

摘要

The pirn is loaded by guiding the thread through the sheath as far as the shuttle by the bias of a piano-wire type spring 1 mm in dia. and highly compressed. The pirn differs from the usual, specifically, by possessing a metal helicoid on its shaft, 2 mm thick and 3 mm deep. It abuts the usual tensioner of the pirn-carrier to follow the normal cycle of the embedded point.