While inkscape is fairly terrible at exact work, you can do it by using the builtin xml editor. I designed a fully working planetary gear train for a clock in i

While inkscape is fairly terrible at exact work, you can do it by using the builtin xml editor. I designed a fully working planetary gear train for a clock in inkscape. It involves placing mostly rectangles exactly using the XML editor and then using the snapping tools to place other objects relative to these exact positions. place rectangle -> control-shift -> change x and y properties.