A padlock joins a lock body to a U-shaped shackle. Explore a schematic opening sequence and calculate the shackle’s leg spacing, bend radius, overall width and exposed centerline length. These dimensions describe shape, without predicting a security rating.
U-Shackle Geometry Calculator
Enter bar diameter, clear inside width, straight-leg height and a declared opening lift. The worksheet reports exact idealized geometry.
Equation Used
- The shackle is a constant-diameter round bar.
- Its bend centerline is a semicircle and its exposed straight legs are equal.
- The body, bores, locking bar and cylinder are schematic.
- Strength, cutting, picking, impact, corrosion, tolerances, ratings and suitability are excluded.
Calculate the geometry of two equal exposed straight legs joined by a semicircular bend. Opening lift changes the illustrative motion and does not affect the shackle’s fixed dimensions.
Body, U-shaped shackle and two receiving bores
US patent 4,462,231 describes a padlock body and a U-shaped shackle with a long leg and a short leg. The short leg carries a locking notch; the long leg remains guided in the body. US patent 7,036,344 likewise describes two body bores and a shackle that can move from locked to open after the locking assembly releases it.
The animation first raises the rigid shackle by the declared lift and then swings it aside. That sequence is prescribed for inspection; internal timing and clearances are not solved.
Portable closure topology
A padlock provides a portable body-and-shackle closure. This page identifies the generic parts and their geometric relationship only. It is not purchasing, installation, lockout-tagout or security advice.
Declared semicircular U-shackle geometry
S is leg center spacing, R is bend centerline radius and Lc is the exposed centerline length. These are geometric identities, not strength equations.
Declared geometry example
For d=10 mm, g=40 mm and h=55 mm, leg center spacing is 50 mm, bend radius is 25 mm, overall width is 60 mm and exposed centerline length is 188.54 mm.
Limits of the shackle geometry calculation
Real padlocks differ in body construction, shackle retention, locking elements, key cylinders, materials and tolerances. Product security requires standardized testing and manufacturer data.
Locks with similar external dimensions can have different materials, internal construction and tested ratings. The shackle geometry alone cannot compare their protective performance.
Padlock geometry questions
Does bar diameter determine security?
No.
Is the opening lift a product specification?
No; it is a declared display dimension.
Does the animation reproduce a particular lock?
No; it is a generic patent-grounded topology.
Can this calculator compare products?
No.
Does the geometry establish a security rating?
No.
Padlock references
- US Patent 4,462,231, Padlock: body member, U-shaped shackle, long leg, short leg and locking notch.
- US Patent 7,036,344, Padlock: two shackle bores, movable and rotatable shackle leg, locking assembly and open/closed states.
- US Patent 5,678,431, Structure of padlock: cylindrical body, detachable shackle end, lock hole and key-controlled locking plate.
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