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Testbed lifting procedure

This page describes how to safely lift a testbed in order to increase the inclination angle.

Before you begin

  • Have a buddy. Do not attempt to lift the beds alone.
  • Make sure you are wearing steel-toed shoes or steel-toed shoe covers (these are available in the shed).
  • Read the instructions for the ratchet jacks if you are not already familiar with them.
  • Never put any body part underneath any part of the beds while lifted.
  • Check your buddy to make sure they are being as safe as you are!

Lifting the box

  1. Retrieve the following items from the shed:
    • Two ratchet jacks
    • Rope (3/4″ diameter polypropylene twisted rope)
  2. Position the gantry at the end of the box you intend to lift with all of the anchor points on it.
  3. Position the ratchet jacks underneath the box on the same end.
  4. Inspect the ropes. Check the visible areas of the rope harness on the box for obvious degradation. Flake and inspect the tie-in rope.
  5. Check the tie-in points on the box. Push sand away from the bolts and make sure that the bolts, washers, and nuts look normal and healthy.
  6. Tie in the box to the gantry by tying a figure-eight or bowline knot around either the I-beam, or the vertical beam on either end. Loop the rope through the carabiners and through the I-beam clamps.
    • The points of contact will be marked at the box side with two opposing oval locking carabiners. Most of them will be to hangers; two will be to the rope harness.
    • Use half of the points of contact on the box for each load-sharing knot system.
    • Make sure you do not exceed 20 degrees between loops down to the box in order to maximize the rope’s load-bearing potential.
  7. With your buddy, lift the box using the two ratchet jacks. You and your buddy should take turns ratcheting the box up.
  8. For every foot of increased height, add an alpine butterfly knot to take up the slack. Listen for creaking. As you can see the (previously invisible) parts of the rope harness, inspect the rope visually for obvious problems. With the twisted rope, degradation should be visually very obvious.

Safety considerations

  • A generous weight for the sandbox is 20×50lbs for the sand + ~16×15lbs for the lumber = 1240lbs.
  • Ratchet jacks: part number 2925T7 from McMaster, rated for 1250lbs up to a height of 4′.
  • A single 1/2″ bolt in wood should have a working load limit of 840lbs; this is why we have so many tie-ins.
  • The hangers are designed to be loaded from the side and are each rated for 67000lbs.
  • The hangers connect to opposing oval locking carabiners, which will protect the rope from sharp edges on the hangers. Each carabiner is rated for 5400lbs when properly closed. When improperly closed, individual carabiners are rated for 1600lbs.
  • The gantry is rated for 4000lbs.
  • Polypropylene rope was chosen for the load-sharing knot systems. This is not a standard choice and the rationale may be found here.

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