I'm building a linear actuator and I don't have much experience with magnetic circuits... A rough sketch of what I'm building is attached. I'm trying to determine if the materials I'm using for the shaft and shaft collar will have a detrimental effect on overall force output. Right now, my shaft is made of 1566 steel and the shaft collars are zinc plated steel (don't know the material number, but it is magnetic). I've noticed that when the shaft, magnet, and shaft collars are assembled that the attractive force of the magnet is reduced vs. when the magnet is by itself. (I'm just putting a piece of metal close to it and felt the attractive force). I'm assuming that the shaft has a low magnetic reluctance and is directing a good bit of the flux through the shaft, but i'm not sure. I'm also assuming that this would reduce the performance of the actuator (overall force). My plan is to replace the shaft with a 303 stainless steel shaft and nylon or aluminum shaft collars. Would this be a sound plan? Could someone explain what is happening to the magnetic field in this application? Thanks.