Historical Background of AS Schild 13L Movements
The story of A. Schild S.A. (also known as AS or ASSA) is deeply intertwined with the golden age of Swiss industrial horology. Founded in 1896 by Adolph Schild in Grenchen, Switzerland, the company quickly established itself as one of the most prolific and technically adept manufacturers of ébauches—raw, unadjusted watch movements supplied to finished watch brands. By the early decades of the twentieth century, A. Schild was a cornerstone of Swiss watchmaking, renowned for producing robust, highly reliable, and standardized calibers that powered timepieces around the globe.
Among the vast catalog produced by Grenchen's master watchmakers, the 13 Ligne (13L) platform emerged during a pivotal era in horological history: the transition from pocket-borne timepieces to wrist-worn instruments. Originally designed for small pocket watches, pendant watches, and high-grade ladies' lapel timepieces, the 13L movement measured roughly 29.33 millimeters in diameter. During the First World War, as officers and artillerymen realized the impracticality of fumbling in pockets under fire, watchmakers began adapting these exact 13-ligne movements for wrist wear, paving the way for authentic WW1 trench watches.
Because A. Schild produced these calibers in significant volume for various third-party brands and private labels, the 13L architecture underwent several subtle variations in bridge layout, winding keywork, and finishing. Despite these surface-level differences, the fundamental integrity of the AS Schild 13L movement remained constant. Its excellent proportions, stable rate keeping, and robust balance staff design made it a favorite among bench watchmakers in the 1910s and 1920s—and those exact same traits make it a primary candidate for modern restoration masterworks today.
Technical Specifications and Movement Architecture
From a bench watchmaker's perspective, analyzing the mechanical layout of the AS Schild 13L reveals classic early-20th-century Swiss design ethos. The "13L" designation refers directly to its raw movement size in French Lignes—13 Lignes translates mathematically to approximately 29.33 mm (1.15 inches) in diameter, with a overall movement thickness typically ranging between 4.0 mm and 4.5 mm depending on the specific train bridge configuration. It operates at a traditional beat frequency of 18,000 vibrations per hour (vph), or 2.5 Hz, yielding that unmistakable, deliberate, and resonant tick characteristic of vintage slow-beat movements.
The standard architecture of the AS 13L features a traditional finger-bridge or split-bridge layout, separating the barrel bridge, center wheel bridge, third and fourth wheel bridge, and balance cock. Most variations were delivered in 7, 15, or high-grade 17-jewel configurations. High-tier executions incorporate screw-set chatons, polished steel cap jewel settings, and a cut bimetallic compensation balance wheel paired with a blued steel Breguet overcoil hairspring. The escapement is a classic Swiss straight-line lever, utilizing synthetic or natural ruby pallet stones secured with traditional shellac.
The keyless works (winding and setting mechanism) present in the 13L platform vary depending on the exact generation. Earlier iterations frequently utilized a pin-set system—where a small pusher beside the crown must be depressed with a fingernail while turning the crown to set the time—whereas later 13L builds incorporated a modern positive stem-pull setting mechanism. The mainspring barrel is driven by a traditional click and click-spring assembly mounted directly on the ratchet wheel bridge, offering smooth winding feedback and consistent power delivery across its typical 36- to 40-hour power reserve.
Challenges of Converting AS Schild 13L to Wristwatch
When you attempt to convert as schild 13L pocket watch into wristwatch configurations, you immediately encounter technical obstacles that stem from the movement's original intended environment. Unlike modern wrist watch calibers engineered from scratch to withstand the shock, orientation shifts, and environmental exposure of an active wrist, early 13L pocket watch calibers were designed to sit vertically in a vest pocket or lie flat on a nightstand. Overcoming these mechanical realities requires meticulous hand-fitting and traditional horological problem-solving.
The primary hurdle during an as schild 13L pocket watch to wrist conversion involves the spatial layout of the sub-seconds register relative to the winding stem. The vast majority of 13L pocket watches feature an open-face (Lépine) layout, where the winding stem sits at 12 o'clock and the small running seconds hand is positioned directly opposite at 6 o'clock. If you simply rotate this movement inside a standard wristwatch case so the crown sits at the conventional 3 o'clock position, your running sub-seconds subdial rotates to 9 o'clock. While a 9 o'clock sub-seconds layout is historically accurate for early conversions, achieving a conventional 6 o'clock seconds register requires finding a rare hunter-cased (Savonnette) 13L caliber, where the original stem was located at 3 o'clock relative to the dial.
A second major challenge is shock protection—or the complete absence of it. The AS Schild 13L utilizes fixed balance jewels press-fit or set in chatons, leaving the balance staff pivots vulnerable to sheared pivots if dropped or subjected to heavy wrist impacts. Furthermore, securing the vintage movement inside a modern housing requires custom-machining specialized casing rings, because original pocket watch cases relied on different case-screw angles, rim dimensions, and bezel snap tolerances than contemporary wristwatch cases.
Lug Welding and Case Selection
Selecting the correct housing is perhaps the most crucial aesthetic and mechanical step when you decide to convert as schild 13L pocket watch movements into modern timepieces. The physical dimensions of the movement dictate the internal geometry of the case, making precision measurement with digital calipers essential before sourcing or fabricating a case.
Watchmakers undertaking this project generally choose between two distinct methodologies: vintage case modification with soldered wire lugs, or modern custom CNC-machined conversion cases. If your goal is historical authenticity, modifying an original sterling silver or nickel pocket watch case involves desoldering the original pocket watch bow and pendant, followed by silver-soldering custom wire lugs (typically 18mm or 20mm wire loops) directly to the case flanks. This closely mirrors the techniques used by bench watchmakers during World War I, yielding an authentic vintage profile that complements projects featured in our guide to antique pocket watch conversions.
Conversely, if daily wearability, water resistance, and structural rigidity are your priorities, a modern stainless steel conversion case is superior. When evaluating modern options, determining the best case size for as schild 13L conversion comes down to scale and proportion. Because the AS 13L movement measures 29.33mm, the optimal external case diameter falls between 36mm and 38mm, with an internal casing seat machined to approximately 29.5mm. This case size provides enough room for a lightweight brass or stainless steel movement holding ring while retaining ideal, classic dress watch proportions on the wrist—avoiding the overly bulky 44mm+ profiles common in 18-Ligne pocket watch conversions.
Crown and Stem Solutions
Fabricating a reliable winding and setting assembly is often where conversion projects hit technical roadblocks. The winding stem of an AS Schild 13L was engineered to mate with pocket watch crowns and pendant tubes, which feature dimensions vastly different from standard modern wristwatch crowns. Modern conversions require precise lathe work or specialized stem extensions to bridge the gap between vintage keyless works and modern case tubes.
First, the watchmaker must evaluate whether the movement utilizes a positive or negative setting mechanism. In positive-set 13L calibers, the setting lever inside the movement dictates the crown position (pulled out for time-setting, pushed in for winding). In negative-set movements—common in American-market pocket watches but occasionally found in Swiss exports—the detent mechanism sits inside the case neck rather than the movement. Convert a negative-set AS 13L, and you must incorporate a specialized conversion sleeve or adapt the keyless works using custom-fitted setting springs to convert the action to a standard pull-out system.
Stem threading presents another hurdle. Vintage AS 13L stems often feature non-standard metric threads or legacy thread pitches (such as Tap 8 or Tap 10). Modern wristwatch crowns typically utilize Tap 9 (0.90mm) threads. To solve this, the watchmaker must either turn a new custom stem from high-carbon steel rod stock on a watchmaker’s lathe—hardening and tempering the finished piece—or carefully fit a hardened steel stem extender secured with thread-locking compound. The crown itself should be selected to match the overall period aesthetics; pumpkin, onion, or oversized flat crowns work best while providing sufficient grip to wind the mainspring without applying excessive lateral pressure to the winding arbor.
Dial and Hand Considerations
The dial and hands serve as the visual center of any conversion, yet working with original vintage 13L components requires delicate handling. Most original AS Schild 13L pocket watches feature double-sunk or single-sunk vitreous enamel dials fired on copper baseplates. While porcelain enamel dials never fade or degrade from UV light, they are extremely brittle. Tightening casing screws improperly, flexing the dial during removal, or exerting uneven force when setting hands can instantly cause catastrophic spiderweb cracking across the enamel face.
If you retain the original enamel dial during a conversion, the dial feet orientation becomes a critical factor. Rotating the movement inside a new case to place the crown at 3 o'clock means the original dial feet will no longer line up with the 13L mainplate securing holes. Horologists address this in one of two ways:
- Carefully removing the original copper dial feet and soldering new feet in the rotated position using low-temperature silver solder or specialized dial-foot soldering rigs that isolate heat away from the enamel surface.
- Utilizing non-invasive mechanical dial clamps or high-tack horological adhesive pads (dial dots) if the dial base is metal rather than fragile enamel.
Hand fitting presents its own mechanical challenges. The original hour wheel, cannon pinion, and fourth wheel pivot dimensions on early 13L movements were hand-finished and vary slightly from batch to batch. Typical post diameters for a 13L are roughly 1.50mm for the hour hand, 0.90mm for the minute hand, and 0.20mm for the small seconds pivot. Original blued steel spade, Breguet, or Cathedral hands should be retained whenever possible. If original hands are damaged or missing, modern replacement hands must be meticulously broached or re-bushed on a staking tool to ensure a friction fit without binding against each other or scraping the inner surface of the crystal.
Why 13L is More Common for Conversion
In the world of custom horology, bench watchmakers and collectors frequently choose the AS Schild 13L over other vintage movements. Understanding why this caliber dominates conversion benches requires examining movement sizing dynamics, historical availability, and structural proportions.
The primary advantage of the 13L platform is its physical size relative to modern wrist wearability. Larger pocket watch calibers—such as 18 Ligne or 19 Ligne movements (measuring 40mm to 43mm across)—require modern conversion cases measuring a massive 45mm to 48mm in overall diameter. These oversized conversions often feel unbalanced, heavy, and awkward on the average wrist. By contrast, a 13 Ligne caliber sits at roughly 29.33mm, allowingwatchmakers to build sleek, perfectly proportioned wristwatches with cases ranging from 35mm to 38mm. This puts the finished timepiece in the quintessential vintage size range favored by purists, comparable to legendary early wristwatches like those seen among historical vintage Rolex wristwatches utilizing contemporary 13-ligne Rebberg movements.
Furthermore, A. Schild produced the 13L platform in substantial quantities over several decades, meaning donor movements, spare parts, balance staffs, and mainsprings are readily available on the secondary market. The movement architecture is straightforward, logical, and forgiving to work on, offering brilliant bridge aesthetics, spacious gear train layouts, and thick plates that take hand-polishing and decorative angling (anglage) beautifully.
Final Thoughts on AS Schild 13L Conversions
Successfully completing a modern convert as schild 13L pocket watch into wristwatch project bridges historical preservation and practical mechanical engineering. By taking a movement originally built a century ago to sit quietly in a vest pocket and housing it in a robust, wrist-ready enclosure, watchmakers breathe new life into an artifact of Swiss industrial heritage.
Prior to final casing, every AS Schild 13L movement must undergo a full mechanical overhaul. This includes completely dismantling the gear train, cleaning all components in ultrasonic baths, inspecting pivot jewels for wear, installing a fresh mainspring formulated to modern torque tolerances, and lubricating friction points with modern synthetic oils (such as Moebius 9010 for high-speed pivots and HP-1300 for heavy gear train arbors). Positional timing adjustments should be executed across at least four positions (Dial Up, Dial Down, Crown Down, Crown Left) to account for the dynamic movement experienced on a human wrist.
When executed with precision, patience, and respect for horological tradition, an AS Schild 13L conversion yields a unique timepiece. It combines the tactile soul, slow-beat cadence, and hand-finished charm of an early-20th-century Swiss pocket watch with the daily utility and modern style of an artisan wristwatch.