Curious Padlock: Corkscrew Key, Spiral Keyway and Bolt Calculator

A spiral passage controls key entry

The numbered entrance cylinder changes the phase of the first part of the keyway. When its passage aligns with the inner passage, the matched corkscrew key can rotate and advance. Its tip eventually contacts the lower face of a bent sliding bolt; further advance withdraws the upper nose from the shackle notch.

The animation opens the shackle only after the bolt has cleared it. It then seats the shackle before withdrawing the key and allowing the spring to return the bolt. The opening and closing are prescribed inspection motions, not a claim that the key powers the shackle.

Dial 7 is the chosen alignment for this demonstration. Other positions stop the key at the entrance-to-inner-passage interface. The historical illustration does not establish a particular number or combination.

Measure key travel and the number of turns

Contact depth is the axial distance from first entry to the bolt face. Bolt engagement is the withdrawal needed to clear the illustrated shackle notch. The model adds 1 mm of clearance travel after release so the open state is visible.

Keyway lead is axial advance per full key revolution. A smaller lead requires more turns for the same insertion, and the animation changes the spacing of the key’s coils to match. The helix has an illustrative 3 mm centerline radius.

The cutaway illustrates key and bolt motion. Housing proportions, guide blocks, spring, dial graduations and the 1 mm overtravel are schematic rather than measured manufacturing dimensions.

Helical key geometry

For keyway lead P, rotation θ advances the key axially by z=Pθ/(2π). Let D be the depth at first bolt contact and b the required catch withdrawal.

Turns to clear catch=(D+b)/P

Full demonstrated travel includes 1 mm beyond clearance, so its turn count is (D+b+1)/P. At current insertion z, bolt withdrawal is max(0,z−D). The catch is clear when that withdrawal reaches b.

For helix radius r=3 mm, the path length of the key tip over axial distance Z is Z√[1+(2πr/P)²]. The displayed path length uses Z=D+b+1. It is a geometric travel distance, not axial insertion or a force estimate.

The correctly aligned key rotates and translates together: a material point with local axial coordinate u has position x=z+u and angle 2πz/P+2πu/P. Therefore its phase at any fixed axial location is 2πx/P, matching the stationary spiral passage.

40 mm contact depth with a 5 mm lead

With D=40 mm, b=1 mm and P=5 mm per turn, the key needs 8.2 turns from first entry to clear the catch. The illustrated extra clearance gives 42 mm total insertion and 8.4 turns to full bolt withdrawal.

At full insertion the bolt has moved 2 mm: 1 mm to clear the notch and 1 mm of extra travel. With a 3 mm helix radius, the key tip travels about 163.81 mm along its helical path.

Changing the dial away from the demonstration alignment prevents the key reaching the bolt. The required-travel calculations remain visible, but current bolt withdrawal stays zero and the shackle stays closed.

Keyway arrangement and model limits

Hiscox’s figure 1145k identifies a corkscrew-like key, a rotating cylinder with a spiral keyway and graduated face, an internal spiral passage, and a bolt pushed back by the key. Those features are represented here.

The keyway, bolt and shackle are shown as an ideal geometric sequence. Actual clearances, spring behavior, friction and wear depend on the lock’s construction.

The model does not calculate operating torque, friction, spring force, strength or resistance to tampering. It cannot establish the security of a lock from geometry alone. The open section explains the movement rather than reproducing all of an original lock’s internal construction.

Curious padlock questions

What admits the spiral key?

The rotating entrance cylinder admits a matched spiral key when its keyway aligns with the internal passage.

Does turning the numbered dial directly pull the bolt?

No. The dial aligns the entrance passage. The advancing key subsequently pushes the bolt.

Why does a smaller lead take more turns?

Each revolution advances a smaller axial distance. Required turns equal axial travel divided by lead.

Why does the shackle stay closed with the wrong number?

The illustrative entrance and internal passages are misaligned, so the key cannot reach the bolt. Insertion stops at the misaligned passage.

Is 7 the original lock’s combination?

No. It is an explicitly chosen demonstration setting. The source does not specify an original setting.

Does the key lift the shackle?

The key retracts the bolt. Opening and closing the released shackle are separate prescribed movements in the animation.