projects / rock screen
Rock screen
A pool's worth of river rock came out full of roots, leaves and dirt. This is the jig that puts it back into 50 lb burlap sacks clean: a 1/2 in hardware-cloth tray at counter height that you shovel onto, bounce, pick over and hose, then tilt with a handle so the rock slides down a plywood funnel into a sack standing on a hand truck. The full sack rolls away; nothing heavy is lifted off the ground.
// by the numbers
- 21 x 36 in at 35 in
- 3/4 to 4 in rock
- 45 lb, 3 shovels
- $190 plus sacks
// what was decided
One tray does every stage. It hangs on two carriage bolts 9 in behind its discharge end and rests on two hockey pucks at the back, so it can be bounced to drop the dirt and then lifted into a 35 degree slide without unlatching anything. Putting the pivot back from the end means the tray's own weight in front of it offsets the load behind, so the handle takes about 23 lb with three shovels of rock on the screen, and the lip swings down into the funnel mouth rather than past it.
The sack sets the numbers. River rock runs 100 lb a cubic foot and a 50 lb burlap sack filled to the top would weigh 120 lb, so the rule is three shovels, 45 lb, about 8 in of rock in the bottom of the sack. The 9 x 9 in spout is sized to fit inside the sack's 40 in mouth with room for the cuff, and it sits 13.5 in off the ground so the sack stands on a hand truck's nose plate while it fills and rolls to the pallet afterwards. Two 8 in wheels on the front legs let the stand follow the pile.
// the drawing set
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Design basis
What was decided, the rock and sack assumptions, and the numbers behind the 45 lb sack rule: rock at 100 lb a cubic foot, three shovels a sack, 60 sacks a yard, 23 lb at the handle.
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General arrangement
Side elevations at rest and tilted 35 degrees with the hand truck in place, the six-step workflow for one sack, and the clearances that must hold if anything is moved.
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Tray
Plan and section of the 24 x 48 in 2x6 tray: 1/2 in hardware cloth on 2x2 slats, battens over every cut edge, the pivot holes, the handle dowel and the flashing lip.
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Stand
Back elevation and top-frame plan of the 2x4 stand: legs outside the stringers, the puck rail, carriage-bolt pivots and the 8 in wheels on the front legs.
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Funnel and sack station
The 3/8 in plywood hopper on the front legs, 26 in mouth to a 9 x 9 spout, and how a 50 lb sack cuffs onto it on the hand truck.
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Cut list
Every board and every plywood piece, board by board.
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Shopping list
About $190 at Home Depot, with the sacks as a running cost.
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Build sequence
An afternoon: tray, then stand, then hang the tray and fit the funnel to it.
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Operating guide
Setting up by the pile, the per-sack rhythm, sacks and storage, maintenance.