Greetings from the US. I'm looking into building something close to a Willoughby to use in finding diamonds at the Crater of Diamonds in Arkansas. The Willoughby technique is very close to what I do with my classifying screens and saruca. One thing I haven't seen described so far is how strong the spring should be. Does it support the whole weight of the screen and gravel, or just assist? Or does it work okay either way. One other thing I haven't seen described is what happens during the washing. Does the arm hit a hard stop at either the bottom or top of movement, or is it a soft stop wherever the person running it decides to go the other way? This inquiring mind would like to know a bit more about the specifics before I take a day to build something, and then a day and a half to drive to where I'll use it.
I saw someone say they have problems flipping the gravel. If you watch one of the youtube videos about using a saruca (including mine) you'll see how we've learned to flip the screen so the gravel doesn't get thrown all over the place. It's a simple technique and gives good results once you try it.
Best of luck to all, and please share any info you can about the spring and the movement.
Thank you.