Cases

Knowledge and Understanding

1 Shapes of Wristwatch Case

There are too many shapes of wristwatch cases to name, other than maybe a few classic designs which are worth mentioning.

1.1 Round Case

The round case is still extremely popular, as it allows the biggest dial area for the size of the case and is an exceptionally versatile form. Also, it is the easiest shape to make water resistant. Apart from the earliest 20th-century wristwatches, round cases are extended top and bottom to include integral lugs to which the strap or bracelet is fixed. Very early wristwatches sometimes had separate strap bars soldered to the case, but these are rare nowadays. With few exceptions, round watches use round backs.

2. Rectangular Case and Tonneau

Two other shapes that have a timeless elegance are the rectangular case-figure 1 and the tonneau- figure 2. The tonneau is basically rectangular but has slightly bulging sides (and sometimes the top and bottom edges bulge, too), giving it a cushion-like shape -see figure 1.  The word “tonneau” is French for “barrel”. 

Figure 1
Figure 2

 Some rectangular and tonneau watches are curved when looked at edge-on, so they follow the curve of the wrist and thus fit very closely and neatly. Early rectangular and tonneau watches were fitted with rectangular movements and had rectangular backs. In modern watches, the curve is just built into the case.

Gradually, some manufacturers introduced the tonneau case for round movements by soldering a counter into the case — essentially an adaptor which fitted into the case and had a circular hole in the middle for the movement. The counter also had a rim to which a round, snap-on back would be fitted. In the late 20th century, the practice was abandoned, and nowadays rectangular cases with the appropriate machined round opening are commonplace.  

Another classic design of women’s watch — still popular to this day — is the baguette. This is a long, slim rectangular form that is almost always curved to fit the wrist more closely-figure 3

Figure 3

2 Casing Rings

Watch manufacturers like to sell their watches in a vast range of different sizes and shapes. However, watch movements are expensive to develop, and it would be prohibitively expensive to make a movement especially to fit each shape and size of case.

Instead, watch manufacturers have a range of standard movement shapes and sizes which they use for all their watches.

A large case could hold a small movement simply by machining only a small hole in the middle of the case. However, this makes the case very heavy and uses a lot of material. Instead, manufacturers make the case with a much larger hole, and then use a plastic- see figure 4 or metal adaptor ring — a case ring — to position the movement in the case. The outer edge of the case ring matches the case opening, and the inner matches the shape of the movement.

Casing rings are called by many names today but are typically made of plastic in lower grade watches and machined metal in higher grade watches-figure 5.

Figure 4
Figure 5

Some casing rings are screwed down to keep a movement secured in the case.

When a new style of case is designed, all that is required is for a new case ring to be designed to hold one of the manufacturer’s standard movements. The same case could have a different movement fitted simply by using a different case ring.

The case ring allows any shape or size of movement to be used in any shape or size of case (provided, of course, the movement is not too big for the case).

3 Snap-Back Cases

The two most common types of fastening for the back are snap backs and screw backs.

Snap-backs are the older type. They are cheap to manufacture but have one or two shortcomings. Firstly, it is more difficult (but by no means impossible) to make them water-resistant, especially after repeated opening and closing, as the snap action must compress the gasket sufficiently without the risk of the gasket popping the case open again. This will always need to be done with a press.

Secondly, snap back cases are opened by forcing a blade between the back and the body of the case. This always runs the risk of leaving a mark, although use of the proper opening tool does mitigate the risk. Many snap backs have lips to make opening easier- figure 6

figure 6

The snap action is achieved by snap rings, one on the case and one on the back. The rings must be forced over each other to open or close the case. These must be made quite precisely so that the force required to fit and remove the back is just right, and for it to hold any water-resistant gasket in sufficient compression.

The back is designed to distort elastically very slightly, allowing the snap rings to pass over each other.

Snap backs can be opened a variety of ways, but the most used method is the case knife for lower gade movements are -figure 7.

For cases that require a higher level of protection from scratching, there are specialized professional grade tools like this Horotec case back opener-figure 8.

figure 7
figure 8

Most snap backs will just snap back on with finger pressure, but occasionally you will run into one that needs to be installed with a tool. They make tools specifically for case back installation, but a watch crystal press will work just fine.

The screw back is, in many ways, a better design, although it too has shortcomings. The body of the case has an internal thread cut around the periphery of the opening, and the back has an external thread cut into it. Notches, dimples, or “teeth” are cut into the back so that the blades of a case opener can engage with them and unscrew the back — see Figure 9.

figure 9

4 Screw Back Cases

One minor disadvantage of the screw back is that it is easy to cross the threads. Although this should never happen to a professional horologist, it does happen, and great care must be taken to ensure the threads are correctly engaged before tightening the back.

Another — perhaps theoretical — shortcoming is that as the back is screwed down onto the gasket, it subjects the gasket to powerful shearing or “tearing” forces as the back turns against the gasket. To reduce the possibility of tearing or distortion, gaskets should be moistened with silicone grease before fitting, which also lubricates the screw thread when the back is screwed down as well as improving their water resistance qualities.

Russian watch manufacturers adopted a rather elegant solution, in which the back is placed into position, and then clamped down by a separate, threaded retaining ring. This means the back is not rotated against the gasket, eliminating a possible cause of damage or distortion — Figure 10 and Figure 11

Figure 10
Figure 11

4.1 Screw-Back Removal

Screw on backs can be removed many different ways.  The first is with a soft rubber ball- figure. The ball is pressed onto the back and twisted. The friction of the rubber works well as long as the back is not on too tight. The best use of the rubber ball is to screw on the back to ensure that you are not cross threading the back-figure 12.

The next option is using a two-prong wrench-figure 13. Once you start putting steel onto steel, you run into the risk of scratching the case back. The two-prong wrench, is the least desirable tool due to its high probability of slipping and damaging the watch. The use of a case holder is strongly advised to securely hold the movement while trying to turn the tool to open the case back.

Figure 12
Figure 13
Figure 14

A better option is the Jaxa wrench-figure 14. The Jaxa tool has 3 adjustable prongs so you will get better leverage. It also comes with different tip styles to handle different size movements and notch styles. The downside to these first two tools is that when the case back as been tightened down for an actual waterproof case. The chances of slipping out the notches goes way up.

The best option is a dedicated bench style case back remover- figure 15. These style openers securely hold the case in a holder which is held in a track under the prongs. Once the prongs are properly spaced for the notches, the prongs get be held in place with a set screw that prevents the prongs from coming out of the notches. The large wheel provides leverage and easily breaks any case back seal. Once the seal has been broken, you can use the rubber ball to finish unscrewing the case back.

Figure 15

Other Types of Screw on Backs

The standard notches in a case back are by far the most common style, but of course there are others.

Rolex Style

The Rolex or oyster style screw on case back-figure 16, has a series of tight ridges around the perimeter of the back- figure 16. These require a special die cup that fits over the notches to be able to grab them so the back can be turned.

There are inexpensive handsets available- figure 17, as well as die sets that work with a bench top opener like Bergeon or Horotec.

Figure 16
Figure 17

Pam or Breitling style case back

These case backs can have anywhere from 10 to 15 sides-figures 18 & 19, so there is no one set of tools or dies to fit all of them. Just like the oyster style back there are wrench style openers-figure 20 and there are also dies available for the bench top openers-figure 21.

Figure 18
Figure 19

 

Figure 20
Figure 21

If you are a home watchmaker, the quality of the watches you will be working on will greatly dictate the type of case opener you want to use. Hopefully it should be obvious that if you are working on a Rolex, Panerai or Breitling, you don’t want to take any chances damaging the case. If this is what you’re going to be working on you definitely want to get a bench top opener.

That doesn’t necessarily mean that you have to buy a Burgeon benchtop opener. This is one of those areas where a Chinese clone that has specialty dies for Pam or Rolex style case backs may not be available as an ad-on so pick your bench top model wisely.

Opening Vintage Pocket Watches

There are many types of systems that case makers used to seal watches into their cases. Here is a video from a friend of mine that covers all the different styles of cases and how to open them.

5 Three-Piece Wristwatch Case

The three-piece case consists of a main body (a) with a removable back (c) and a removable bezel(b) — see Figure 22. The bezel is almost always snapped on, whereas the back may be snapped or screwed. The bezel often has a very tight snap action, as they need to be removed far less frequently. Always look around the bezel for a notch for inserting a case knife.

Figure 22

Three-piece cases tend to be associated with better quality watches, although modern manufacturing techniques make this association a little tenuous. A three-piece case allows the body and the bezel to be made — or plated — with different materials, which can give an attractive appearance to the watch — see Figure 23 & 24

Figure 23
Figure 24

Dive watches would fall into this category as well. Dive watches most often have a rotating bezel that a diver would use to time how long they could stay under water depending on how much air was in their scuba tank. Diving bezels most often have a removable bezel insert that sits in a groove on the top side of the bezel itself so that it can easily be replaced.

6 Two-Piece Wristwatch Case

Most two-piece watch cases have the bezel and body integrated into one piece or a body with no bezel at, all along with a removable back and are by far the most common style of watch case. Two-piece watch cases can utilize any number of back styles like snap back, screw on or screwed on backs— see Figure 25.

Figure 25

However, in the early to mid-20th century, the opposite arrangement was sometimes used with the back and body made as one piece, along with a removable bezel. These are commonly known as monocoque (pronounced maa·now·kaak), cases or as a front loader.

 In these watches, the movement is withdrawn from the front of the case after the bezel and crystal have been removed

Watches with monocoque cases are typically seen in higher end watches as the cost to manufacture a case from a single block of metal is much more than cases cut from multiple pieces. There are also many advantages to front loaders. They tend to be more rigid, there is no chance of a back gasket failing and allowing water inside and they often have a flat back making it a very comfortable watch to wear.

There are many ways that manufacturers have utilized this style of watch case, but they all share one thing in common, the movement is installed from the front of the watch. Here you can see an example of the Patek Philippe Nautilus with a monocoque case. Notice that even with a separate back this is considered a monocoque because the movement is still installed from the front.

There are many ways that manufacturers have utilized this style of watch case, but they all share one thing in common, the movement is installed from the front of the watch. Here you can see an example of the Patek Philippe Nautilus-figure 26, with a monocoque case. Notice that even with a separate back this is considered a monocoque because the movement is still installed from the front.

Figure 26

With the multitude of different front loaders manufactured, many with their own procedure for disassembly, uncasing them should be approached the following way to prevent potential damage.

6.1 Remove the Crystal

Crystals are going to be held in either as a compression fit, armored or with a tension ring. We will be going into much more detail in later lessons on crystal removal and replacement.

Start by removing the bezel with a good case knife or bezel removing tool. Make sure to look for a notch between the bezel and body of the case to slip the blade or bezel opening tool into. It’s also possible there is no removable bezel so make sure there is a visible seam between the bezel and body.

Figure 27

Compression fit watch crystals fit into an angled groove around the case opening. The opening that the crystal fits into is roughly .20 to .30 mm  smaller than the outside diameter of the crystal. See figure 27

If the crystal is a compression fit, you can use a standard crystal lift to remove the crystal by slightly tightening the lift on the crystal until it is compressed enough to pull out- figure 28.

Figure 28

Armored crystals have a tension ring inside the crystal that will just lift out after the bezel has been removed. The bezel usually holds it in place. Armored crystals can sometimes also be removed with a crystal lift but should be installed with a crystal press which we will be covering in the next part 2 of this lesson.

There are also watches that have a flat watch glass. There are a couple different ways to remove flat glas. The first is to with a crystal pump. Pressurized air is forced into the case through the stem tube and and the air pressure will force the watch glass to pop out. See figure 29

Figure 29

The second way to remove the glass is with a mini suction cup. See Figures 30 & 31

Figure 30
Figure 31

Once the crystal has been removed, you need to analyze the opening to determine how the stem is to be removed. Both single stem and split stems are used in front-loading watch cases.

 6.2 Notched Case

The simplest to identify and remove is when the stem is sitting in a notch that has been cut into the case for the stem to sit in like on this Rado watch case- see figures 32 & 33.  When the case is assembled, the bezel covers the notch and holds the stem in place. The movement should just lift out.

Figure 32
Figure 33

6.3 Single Stem (access through dial)

 A single stem used in a front-loader that doesn’t have a notch needs to be released somehow from the movement. In this Seiko, there is an opening at the edge of the dial to give access to the stem release -See figure 34.  

Figure 34

If there is no access found to a stem release lever, look for a ring round the dial that locks the movement in place-See figure. In some cases, the ring will need to be turned to unlock the movement from the case and to gain access to the release lever.

6.4 The Split Stem

The split stem has two parts. The female end is secured into the movement with the setting lever and the male part of the stem is attached to the crown-See figure 35.

Figure 35

On some monocoque case watches with split stems,the connection point will be outside the case tube and you will be able to see the split stem connection when you look inside the case. Turn the crown so that you can see where the male and female part of the stem are connected and then just lift the movement with dial and hands out of the case- see figure 36.

Figure 36

Some split stems have the connection inside the case tube and they will have to be pulled apart to separate them. When you see that the case tube extends behind the dial, that is a good indication that the stem needs to be pulled apart- see figures 37 & 38.  This can be done with a couple different tools-See figures 39 & 40.

Figure 37
Figure 38
Figure 39
Figure 40

Finally, you may occasionally come across some Timex watches which are made as a three-piece case, but during manufacture, the body and back were glued together. In effect, it is a two-piece case, although it looks like a three-piece. Again, the watch is dismantled by removing the bezel and drawing the movement out of the front.

7 Case Backs attached with Screws

You will occasionally come across a watch that has the bezel and/or back held down by screws around the periphery — see Figure 41. The back opens as you would expect. When removing a screwed-down bezel, take extra care not to damage the screw heads — these screws are on permanent display.

Figure 41

Be aware that some bezels have fake screws around them. Do not try to undo them! They are usually very soft, so they will mark easily and often shear off.

8 Watch Case Sizes

We do not talk much about watch case sizes these days. However, up until the early 20th century, it was quite usual to buy a watch and specify the case you wanted.

The size of the case refers to the size of the movement it will take. For instance, an American Pocket Watch size 16 case could be bought from a number of manufacturers, and it would correctly fit a size 16 movement from any of the American watch manufacturers, such as Hamilton, Waltham, Elgin, etc.

The Swiss used the ligne as their unit of measurement: one ligne (pronounced “line”) being roughly 2.256 mm. The ligne is sometimes symbolized as ‘”, e.g., 16 1/2””. The ligne continued as a unit of measurement for watch movements until the latter years of the 20th century, when most manufacturers and suppliers began to quote sizes in millimeters.

You can download a Ligne Conversion chart HERE.

The size of the movement refers to the largest diameter across the plates. Rectangular movements are given two measurements: the widest point along the length and across the width.

9 Watch Case Materials

9.1 Stainless Steel

I have mentioned stainless steel first because it is such a good material for watch cases- figure 42. It is cheap (and thus there is no pressure to make stainless steel watch cases thin and flimsy); it is entirely unaffected by contact with the human body; it is resistant to challenging environments such as moisture, salt air, or saltwater; it is non-magnetic (in the grades used for watch cases); it is tough and durable; and it can be given a range of pleasing finishes. It is not as hard as some metals, so after hard use, it can become scratched or dull. On the other hand, it can readily be polished.

Figure 42

9.2 Platinum

Platinum is very expensive. It is usually alloyed with iridium to make it hard enough for watch cases. It is white in color. The high cost means it is rare in watch cases. See figure 43

Figure 43

9.3 Gold

Gold — when used for watch cases — figure 44, is almost always alloyed to make it harder. The purity is measured in carats. 24-carat gold is pure; 18-carat gold is eighteen twenty-fourths pure; 9-carat gold is nine twenty-fourths pure, and so on.

The common purities for gold watch cases are 9, 14, and 18 carats. You also see the decimal system used to indicate purity. For instance, 18-carat gold is marked .75 and 9-carat is marked .375 to indicate the proportion of pure gold in the alloy.

Gold is alloyed with a range of other metals, including silver, copper, and zinc. Lower carat alloys are harder than high carat alloys. Pure 24-carat gold is the softest of all. The particular choice of metals to alloy with gold affects its final properties, in particular its color.

As well as a pleasing appearance, gold is highly resistant to corrosion and oxidation (although these qualities diminish at lower carat values). In that respect, it would seem to be good material for a watch case. It also has a high perceived (and actual) value, so a gold case is regarded as prestigious.

Figure 44

On the other hand, it is very soft compared with, for instance, stainless steel. In addition, the high cost means that most vintage gold watch cases are often very thin. The softness, combined with the thin construction usually used means gold watch cases tend to be delicate and flimsy. They can be easily damaged, and it is quite common to find dents in them.

Nevertheless, despite these objections, gold remains a popular material for expensive watches.

10 Hallmarking

Hallmarking is an essential process for marking items made from gold, silver, and platinum to ensure their purity. The process dates back to 1300 when the Worshipful Company of Goldsmiths was responsible for guaranteeing the purity of precious metals. Today, hallmarking remains a guarantee for manufacturers, importers, retailers, and purchasers.

Assuming that testing demonstrates the item’s sufficient standard, a series of marks are applied by punches, laser marking, or engraving. Hallmarks must include the sponsor’s (maker’s or manufacturer’s name) mark, the metal and fineness (purity) mark, and the assay office mark. There are assay offices in London, Birmingham, Sheffield, and Edinburgh. The assay office in London also applies two optional marks: the date mark and the traditional fineness mark.

Common Control Mark and Convention Marks

The International Convention on Hallmarks in 1972 agreed that the assay offices in the United Kingdom can strike (stamp) the Convention Hallmark-Figure 45, which is recognized by all member countries in the International Convention. Similarly, hallmarks from other member countries are legally recognized in the UK. Imported items bearing the Convention Hallmark do not need to be re-hallmarked in the UK.

Figure 45

White Gold

White gold is a variant of gold that has been alloyed with palladium in the proportion of six parts gold to one part palladium. It has a white color and is subject to hallmarking. There is no specific hallmark for white gold. It’s marked the same as yellow gold.

Rolled Gold

Figure 46

Rolled gold is made by bonding a plate of gold (of not less than 9-carat purity) to a bar of silver or non-precious metal, and then rolling them together. The final thickness of the gold on the outside is a minimum of 10 microns. A micron is 0.001 mm (a thousandth of a millimeter), so 10 microns is about 0.01 mm or approximately 0.0004 inches.

It’s important to note that 10 microns is very thin, and the gold can easily be removed by polishing or normal wear. Thicker gold layers provide greater durability. Manufacturers would offer cases designed for a certain lifespan, for example, a “20-year case” -figure 46 with a gold thickness of about 0.003 inches (about 76 microns), and a “10-year case” with a gold thickness of about 0.0015 inches (about 38 microns). This information gives an idea of how long a 10-micron layer might last.

It’s important to note that 10 microns is very thin, and the gold can easily be removed by polishing or normal wear. Thicker gold layers provide greater durability. Manufacturers would offer cases designed for a certain lifespan, for example, a “20-year case” with a gold thickness of about 0.003 inches (about 76 microns), and a “10-year case” with a gold thickness of about 0.0015 inches (about 38 microns). This information gives an idea of how long a 10-micron layer might last.

Gold Filled

Gold filling is similar to rolled gold, but a plate of gold is bonded to both sides of the bar of silver or non-precious metal before rolling down. The two plates of gold are not normally of the same thickness. The gold on the outer surface of the manufactured article must be a minimum of 20 microns thick, while the inner layer is usually thinner.

Gold Plated

Gold plating is a more modern technique that has largely replaced rolled and filled gold. The gold is deposited on the underlying metal through an electrolytic or chemical process. The gold must be a minimum of 9 carat purity and have a minimum thickness of 10 microns for the term “gold plated” to be used in marketing material.

Gold plating has a significant advantage as it can be applied after the case has been machined, reducing waste.

A Word About Gilding

The terms “gilding” or “gilt” are often used concerning watch cases, clock parts, and jewelry. Gilding is a generic term for any process of applying a thin layer of gold or something simulating gold to a surface. Gold leaf application to a surface is an example of gilding.

Several modern plating techniques can give items a gold-like or yellow appearance, even without containing any gold at all. Gilding metal, also known as “Pinchbeck,” after its inventor, is an alloy of 85-95% copper with the remaining zinc. It has a gold-like color but is more affordable than gold.

Formal requirements for the thickness of gilding or whether it contains gold are absent. Therefore, the terms “gilt” and “gilding” may mean very little, except that a layer of gold or something simulating gold has been applied.

Silver

Silver is rarely used for watch cases nowadays because it is softer and more expensive than stainless steel, which has a somewhat similar appearance. However, before the 20th century, it was popular as an attractive and lower-cost alternative to gold.

Sterling silver is an alloy comprising 92.5% pure silver and 7.5% other metal. Silver used in watch cases was often alloyed with greater proportions of other metals, especially copper, to make it more durable.

Silveroid

Starting around the 1880’s a nickel composition metal was used in watch cases. This metal looked very much like silver, but it was much cheaper, harder and it didn’t tarnish. Different case manufacturers had their own trademarks/brand names, but most of the names include “silver” as part of their name even though there is no silver in the case. Example trademarks include silveroid-figure 47, silverine, silveride, silverode, ore silver, alaska silver, and nickeloid

Figure 47

9.5 Chromium

Chromium is never used on its own for watch cases, but it is used to plate other metals, most frequently nickel and its alloys. It usually has a bright, shiny appearance and is quite hard and durable. However, it does not resist acid, so prolonged contact with skin can spoil its appearance. It can also cause adverse skin reactions in some people, so it is not used on the backs of watches.

9.6 Ceramic

The late 20th century saw some watch manufacturers introduce ceramic watch cases. There is a wide range of ceramics available. The ones used in watch cases are very hard, tough, and durable. They look very different from metal cases and thus play a valuable role in providing buyers with more choice.

9.7 Plastic

Most people associate plastic watches with the Swatch brand and their range of plastic-cased quartz watches launched in the early 1980s, although plastic had been used for watch cases before then.

Plastics are available in a vast range of colors and textures, providing unlimited possibilities for innovative designs. Most plastic parts are made by injection molding, allowing complex items to be produced very cheaply and in large quantities.

Plastics are generally tough, although they are typically softer than the metals used for modern watch cases, making them more susceptible to scratching. Over time, plastics can age and degrade due to exposure to the ultraviolet component of sunlight. As a result, plastic watch straps may fail more quickly than their leather or metal counterparts.

9.8 Titanium

Seiko can take credit for introducing titanium watch cases to the mass market (see Figure 48). Titanium has a unique dark grey appearance with a soft sheen. Although expensive, it is extremely hard and durable, allowing for thin cases without compromising strength. Additionally, titanium is very lightweight, making titanium watches remarkably light. Its poor thermal conductivity means that the watch does not feel cold when first worn. Moreover, titanium is highly hypoallergenic, making it suitable for people with skin allergies to other metals.

Figure 48

9.9 Others

Nickel has never been used on its own for watch cases but is alloyed with copper and zinc to produce what should properly be called nickel brass. It has a silvery white appearance and is often called nickel silver or German silver, although it contains no silver at all. Due to skin allergies resulting from its use, legislation controls the use of nickel, and regulations restrict nickel content in products that touch the skin. As a result, nickel has not been used in watch cases since the late 20th century.

Aluminum and its alloys have been used for watch cases, although not widely. After machining, it is anodized to give a durable, glossy, colored finish.