That's just my boss grinder. I cobbled it together based on designs from Joe Price and Richard Lewis.
It requires hundreds of spear traps, so you'll need to get your Picksaw back. I stacked a bunch of spear traps in columns, 6 high. You must actuate EVERY spear trap out or it will hit the trap beneath it.
I use a bird statue to turn the grinder on and off. The bird flies for a few feet, triggers a six pressure plates a few milliseconds apart, which are wired to 1 second timers.
I take these staggered signals and wire up all my spear traps so they fire consecutively. The bigger your spear trap stacks, the less downtime you'll have between volleys.
If you choose to use it for boss grinding, don't copy my use of lava; it doesn't work. Lava only stops ground mobs from spawning outside the kill area. Wraiths, vampires, etc., will still spawn, which is less than ideal.
Oh, and spears can actually crit, so roll crit on your gear.