Cheers for your replies. I remember that they aren't the most affective of weapons, but I guess it was more a sort of impulsive idea to think of sticking one on the back.

I guess if that is the case and since I've heard that about starting with lighter machines, I will probably start with a featherweight then. I did actually begin building one when I was 17 for an A Level project, but due to ill health it was never completed and ultimately I dismantled the little work I had done. I guess I could start on that one again as I probably still have a lot of the plans and research stored away somewhere.

Regardless, I know it'll be a quite a challenge but a good education for me. I'm an electrician with a strong interest in electrical engineering, I also regularly work with various metals in my spare time as I'm always creating some project or other. I obviously have some knowledge, but probably a totally insufficient amount to complete this without learning more. So come to think of it, I definitely think the featherweight option makes much more sense as a way to get more knowledge and experience.