helloo okay so i have a praktica b100 with a lot of lenses for it. i also have a nikon d40. i would like to mount my praktica (b mount) to the nikon (f mount) i cant find the appropriate adapter however. im pretty handy in a machine shop, so i could just make my own. i just had a question in regards to the materials. what are most adapter rings made out of? would aluminum be bad for the mounting surface of my d40? what should i opt to make the mount out of?