Possibly the problem stems from newcomers who Google "machinist forums" and join without reading the rules. Perhaps if a popup came up at the signup page that said something like "This is a forum dedicated to industry professionals. Hobby topics and machines are not part of this site. Hobby users might like bbs.homeshopmachinist.net, hobby-machinist.com, and other sites better suited to your needs." That would put people on notice. Post the sites as active links, perhaps.