Pump drill with stone bit
drills wood, bone, shell and soft stone
AWhat it needs
Needs 6 other products in all, 2 of them directly.
- 02.22 Pump drill with stone bitMaking Year 1 needs 6 products
- 01.07 Bow-drill fire setMaking Year 1 needs 3 products
- 01.03 Sharp stone flakeMaking Year 1 needs 1 product
- 01.02 HammerstoneMaking Year 1 raw materials only
- 01.05 Twisted plant-fibre cordMaking Year 1 needs 2 products
- 02.03 Stone knives, scrapers and engraving pointsMaking Year 1 needs 3 products
- 02.01 Knapping kitMaking Year 1 needs 2 products
Open a box to see what it needs. A dashed box is a product already drawn in full: click it to jump there. In the org chart, drag to move around.
BWhy
The bow drill needs both hands and a foot. The pump drill spins by pushing a bar up and down with one hand, leaving the other free to hold the work. It drills neat holes in wood, bone, shell and soft stone, and it is the first tool on the island with a flywheel.
CYou need
- A straight hard rod as long as the forearm and hand, and as thick as a thumb
- A flywheel: a flat round stone with a natural hole, or a disc of heavy wood a hand-span across with a hole burned through its centre
- A cross-bar as long as the forearm, with a hole in its middle a little wider than the rod
- Strong cord, as for the bow drill (01.07)
- A narrow flint borer (02.03)
DSteps
- Cut a slot in the bottom end of the rod. Set the borer in it and bind it tightly with wet cord, so it sits exactly in line with the rod.
- Push the flywheel up the rod from the bottom until it jams a hand-width above the bit. Wedge it there with slivers of wood. It must sit square to the rod, or the drill wobbles.
- Cut a notch across the top of the rod.
- Slide the cross-bar onto the rod from the top. It must move up and down freely.
- Tie a cord to one end of the cross-bar, lead it up through the notch at the top of the rod, and tie it to the other end. The length is right when the bar hangs a hand-width above the flywheel.
- To start: hold the bar still and turn the rod by hand. The cord winds round the rod and the bar rises.
- Set the bit on the work and push the bar down smoothly. The cord unwinds and spins the rod. Ease off just before the bottom: the flywheel keeps turning and winds the cord up the other way, lifting the bar.
- Push down again. Find the rhythm; it is like bouncing a ball.
- For bone and shell, drill halfway, turn the piece over and drill from the other side to meet. This stops the far side breaking out.
- For stone, drip water and a pinch of sand under the bit and let the sand do the cutting.
EIt worked if
- It keeps spinning with one hand, and the bit stays on its mark.
- It drills through a mussel shell in under a minute.
FWhat goes wrong
- It wobbles. The flywheel is not square, or the bit is off centre. Reseat both.
- It stalls at the bottom of each stroke. The flywheel is too light. Use a heavier one, or lash two stones to it.
- The cord slips round the rod. Deepen the notch at the top.
- The bit snaps. Too much pressure. Let the spin do the work.
GIn the story
Hiro builds it in an afternoon from a drawing Zoe scratches in the dirt with a stick, arguing with her about the weight of the flywheel the whole time. Both are right about different things. Yara takes it the same evening for drilling shell buttons, and Hiro has to make a second for himself.