I found the BP for the treadle yours is based on ApprenticeMan, one thing I'm wondering about are the springs. I'm assuming 2? None of the pictures make it clear that there are indeed 2 springs being used. Also how strong should the springs be rated? I found several suppliers of garage door extension springs with ratings from 10 lbs. up to 220 lbs. I'm thinking, roughly twice the weight of the hammer?