Here at Wound For Life, we get on the subject of watch durability rather often – shock resistance, magnetic field resistance, water resistance, you get the idea. What we don’t touch on frequently is movement construction. Today’s article is going to be a bit of a hybrid between a Lesson in Wristory and a Technical Notes, as we discuss the history and evolution of back plate construction in hand wound movements.
While there are overlaps and exceptions to the rule, the general evolution of the back plate starts with the full plate, then onto the three-quarters plate, and finally the full bridge design. Advancements in watchmaking, as well as technology and fashion trends have been the primary drivers in this evolution. This isn’t meant to be a comprehensive history of each type of movement – that would warrant a book – but it shall serve as a good primer, likely sending you off down your own research rabbit holes.
Full Plate Movements
It’s not hard to conceptualize what a full plate movement is. It’s almost exactly what it sounds like. The back plate is entirely, or almost entirely, the size of the base plate, showing no parts of the going train, escapement wheel, pallet fork, or winding mechanism. What you will see is the balance assembly, some screws, and hopefully a nice, decorative plate. Compared to what today’s movements look like, it’s a strange configuration.
A full plate movement from Illinois Watch Company — photo courtesy of American Watch Company
Full plate movements were used in pocket watches predominantly in the mid 1800s through the early 1900s, when mass production was in its early days seeking to meet popular demand. The full plate movement had a couple of advantages that may have pushed watchmakers towards this design. First, the full plate hides the majority of the innards, making finishing of those parts unnecessary, saving time and money. Second, watch cases were not nearly as well sealed as they are today, and the full plate was another layer of defense for keeping dust away from most of the moving parts.
Of course, it wasn’t all good. Full plate movements are thick by nature. Starting with a thick movement only leaves the watchmaker so much wiggle room with case size. As with just about anything else, we prefer our gadgets compact, so there was a growing demand for smaller watches. This grew even truer as wristlets and wrist watches hit the market later on. The other major drawback is the difficulty of servicing. As you may have guessed, if a watchmaker is to service the watch, almost no matter how simple the job, the entire plate must be removed to access the guts of the movement. What can be even more frustrating than disassembly is re-assembly. Many watchmakers use the tactic of “upside down” assembly, essentially flipping the movement over and building from the balance, up. Mass production meant more watches in use, which, as logic dictates, more watches in need of servicing. Thus, a more convenient construction was in order; enter, the three-quarter plate.
Three-Quarter Plate Movement
Made famous by A. Lange & Söhne, the three-quarter plate was a clever next step after the full plate. Instead of keeping the balance assembly on the outside of the back plate, a cutout was made, integrating the balance wheel with the rest of the innards, and leveling the balance bridge with the rest of the plate. The three-quarter plate is what holds down the going train and mainspring, and in some designs, another separate bridge is designated for the escapement wheel.
Lange’s three-quarter plate caliber L051.2 — utterly gorgeous
The most obvious benefit of the new design was a decrease in thickness, an important characteristic for the ever-shrinking watches. Breaking down the back plate into different parts also made servicing much easier, allowing the watchmaker to only remove just a single plate or bridge without disturbing the rest of the movement. For the benefit of the watch lover, the exposed gear train and partial view of the base plate called for a higher degree of finishing. This may have been a drawback for the watchmaker, but it’s certainly nice to look at.
As mentioned, Lange has made this design famous, but the three-quarter plate is in no way monopolized in Glashütte. Many Swiss watchmakers used (and still use) the three-quarter plate, most notably Jaeger LeCoultre, Lemania, and Peseux (one of the ETA origin watchmakers). The three-quarter plate design straddled the changeover line between the pocket watch and wristwatch, around the time between the World Wars, necessitating smaller and smaller movements. But despite the improvements, the next step sought to one-up the three-quarter plate.
Full Bridge Movement
Picking up steam in the 1930s, and carrying on well into the 1970s, the full bridge movement is arguably the most attractive and technologically superior back plate design. The name is aimed at the prototypical bridge that spanned across the width of the movement, holding the center wheel, and sometimes the mainspring, in place. Separate bridges are used for the balance, escapement wheel, the rest of the going train, and the mainspring (if not under the full bridge). Full bridge designs are often found with four or five bridges, but six bridges are not unheard of.
IWC Caliber 83 — showing off an uncommon 6-bridge construction
It’s hard to deny the beauty of a full bridge design. Because of the exposed parts and increased number of edges, finishing must be at its best. Another factor for the movement designer to consider is the shape and configuration of the bridges themselves. There’s no “half assing” the design – the layout must flow and show some sort of cohesion.
Aside from aesthetics, the individual bridges allow easy access to very specific parts of the movement. During the first couple of decades of the full bridge’s reign, service intervals were fairly short, with many folks servicing their watches yearly. With that in mind, it becomes even more obvious how beneficial the design was. Another benefit, although not a universal truth, is the overall higher level of finishing playing a part in performance enhancement – this, in addition to looking sexy. As imperfections are removed, moving parts are more likely to function as designed.
Patek Philippe cal 215 PS — a modern day full bridge design
As far as hand wound movements are concerned, the full bridge construction is the pinnacle. However, the high level of finishing dictated price increases, especially as quartz watches took hold. Mechanical watches were once again luxuries, so manufacturers needed to cut costs. This is partly why many of the movement designs you see today are a bit of a hybrid between the full bridge and three-quarter plate. There’s nothing inherently wrong with current designs; in fact, with service intervals getting longer, four or five separate bridges aren’t necessary.
It seems that many of the current full bridge designs (think Patek, AP, and JLC) are only found in high-end watches, putting them out of reach for the majority. Add in the prevalence of automatic movements, and you get the full picture as to why we rarely get to lay our eyes on new full bridge movements. Vintage is the way to go if you’re looking for the full-bridge aesthetic, namely IWC and JLC (in our humble opinion). You could also spend the rest of your life trying to get your hands on a Philippe Dufour Simplicity — and good luck with that.
We hope you enjoyed this primer on the evolution of hand wound movement designs. This article took a fair amount of research, and we’d specifically like to thank Carlos A. Perez, for his TimeZone articles on full bridge and three-quarter plate movements. They were an invaluable resource.
by 
