In watchmaking, everything matters, but without consistent power, the watch will not run. Understanding how to service the mainspring barrel for automatic movement is one of the things you have to get right.

In our video, Watch Lubrication for Beginners we don’t go get into servicing the barrel, so we are going to dive in right now.

Since 70% of the original power coming out of the mainspring is lost by the time it gets to the escapement, it’s absolutely critical that you give the barrel the ability to do its job.

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Finding and Opening the Barrel Lid

To start, locate the lid as it fits into the barrel, and with the lid facing up, push down on the sides until the lid pops off. This may seem simple, but for first-timers, it can be a bit tricky.

Opening a Mainspring Barrel

Drawing the Mainspring Coil Orientation

Before removing the mainspring from the barrel to service it, it’s a good idea to draw out the orientation of the mainspring coil to ensure that you put it back in correctly.

Drawing Mainspring Orientation
Drawing Mainspring Orientation

Removing the Mainspring to Service the Barrel

To remove the mainspring, take bronze or brass tweezers and get under the inner coil of the mainspring. Slowly turn the barrel until enough of the mainspring comes out so that you can get your fingers under it, then walk the mainspring out of the barrel. This process requires some finesse, and it may take a few attempts to get it right. Make sure to hold onto the barrel tightly.

Removing Mainspring with Tweezers
Removing Mainspring with Tweezers

Inspecting the Mainspring

After removing the mainspring, inspect it to make sure that it’s sitting flat and has not become set or tired. If it has become coned and won’t sit flat on your table, it’s not going to sit flat in the mainspring barrel.

This will cause the mainspring to rub either on the top of the lid or the bottom of the drum, which creates additional friction and lowers the available power out of the barrel. This is an amplitude killer.

A Mainspring that has become Coned
A Mainspring that has become Coned

Purpose of the Mainspring Bridle in a Automatic Barrel

The mainspring bridle creates a release valve inside the barrel that prevents the amplitude from getting too high, which could cause the mainspring to break or the escapement to start knocking.

The curved bridle applies pressure between the end of the mainspring and the greased barrel wall, and when the spring is wound up to a certain point, the mainspring will slip, releasing some of the stored energy inside the spring.

Mainspring Bridle on Automatic Mainspring
Mainspring Bridle on Automatic Mainspring

Inspecting the Mainspring Bridle

In your service of the mainspring barrel, check the bridle to make sure that it looks normal and is not misshapen or bent. If the bridle is damaged, the mainspring will not slip properly, usually unwinding too soon, reducing the power reserve of the mainspring barrel.

Damaged Mainspring Bridle
Damaged Mainspring Bridle

Checking Mainspring Slippage

One of the first things to check when inspecting a watch barrel is mainspring slippage. If the mainspring slips too soon, it can cause faster rates, while if it doesn’t slip at all, it can cause too much amplitude, potentially breaking the impulse joule if the watch is knocking.

Servicing the Mainspring Barrel and Lid

Inspecting the barrel and lid is also crucial. You don’t want to see any gouges or scrape marks on either of these parts, as wear can interfere with the mainspring’s winding and unwinding process, creating additional friction and lowering the amplitude.

Why Some Mainspring Barrels have Grooves

In higher-quality movements, you’ll see grooves machined into the barrel walls. These grooves function as stops for the bridle as it slips inside the barrel, controlling the amount that the bridle can actually slip at any one time. This maintains the highest possible safe amplitude for the mainspring barrel.

Grooves inside Mainspring Barrel
Grooves inside Mainspring Barrel

Checking the Free Running of the Barrel Arbor

The next thing to check is the free running of the arbor inside the barrel. To do this, pre-clean the parts, reinstall the arbor inside the barrel and attach the arbor to an arbor vise. Then, spin the barrel with your fingers and look at the barrel to see how freely it spins around the arbor. The barrel should spin freely and not feel tight as it’s spinning.

Barrel Mounted on Arbor Vise
Barrel Mounted on Arbor Vise

Inspecting the Mainspring Barrel Lid

If the barrel does not spin freely, the first thing to check is the barrel lid. Make sure that the lid is actually flat, as it can become domed in shape when opening up the barrel. Use a straight edge on the top of the barrel to visually see how flat the lid is. If the lid has been dented, it can create extra friction between the arbor and the barrel lid.

Inspecting Barrel Lid for Flatness
Inspecting Barrel Lid for Flatness

Checking for Barrel Bridge Friction

If the lid is domed or crowned up, this can increase the end shake of the arbor inside the barrel, creating slop and possibly rubbing on the underside of the barrel bridge, creating friction that reduces the amplitude.

Correcting Problems with the Mainspring Barrel

Correcting a Domed Barrel Lid

If your barrel lid has become domed, you can easily correct it by using a staking set or a hand-setting pusher. Simply push the barrel lid gently until it sits flat in the barrel. If you’ve pushed it down too far, you can push it back in the opposite direction by pushing on the arbor from the other side of the barrel.

Correcting bent Lid with Staking Tool
Correcting bent Lid with Staking Tool

Checking for Good End Shake

If your barrel spins freely, take the opportunity to visually inspect what a good end shake in a barrel looks like, so you can file this away in your brain as a visual reference for future inspections.

Dealing with Scratches and Egg-Shaped Holes

Scratches inside the barrel arbor holes, in the barrel drum and lid are a common problem caused by excessive amounts of lubrication mixed with grit.

Scratches are always going to be there but if it gets too bad, the holes can become egg-shaped and they will require re-bushing, so if you are new, finding a new barrel may be the best option.

Polishing the Barrel Holes

When polishing the lid or the barrel drum,  insert a toothpick from the outside of the barrel charged with Polinum into the hole, as these barrel arbor holes have a slight taper to them that acts as an oil sink to hold the oil around the arbor.

Using the taper of a toothpick works perfectly for polishing these holes. If the Polinum is not coarse enough for the scratches in the barrel holes, switch to a 0.5 micron diamond paste.

If you can’t find Polinum, Red Rouge also works well.

After polishing, clean the area up and inspect the holes again under high magnification. What you’re looking for is to see the holes shining like a mirror.

Polishing Arbor Holes
Polishing Arbor Holes

Removing scratches inside the barrel holes is crucial to reduce the amount of friction between the barrel arbor and the barrel drum. If the holes in the drum and the lid are scratched, the arbors are also going to be scratched.

Removing Scratches on the Arbor when Servicing Mainspring Barrel

 To polish the arbor, insert the arbor into an arbor vise and use a felt pad in a rotary tool for polishing. Make sure the arbor is secure, so the rotary tool doesn’t throw the arbor across the room.

Slowly push the arbor pivot into the felt until the arbor penetrates into it, and then charge the felt tip with the polish. This works effectively for polishing both the upper and lower parts of the arbor at the same time.

Polishing Arbor
Polishing Barrel Arbor

Clean the arbor again and check to see if all the scratches are gone. If not, use diamond paste and then repeat with Polinum. With all the scratches gone, the arbor should shine like a mirror.

Lubricating the Mainspring Barrel Walls

In manual wind movements, you don’t lubricate the barrel walls, but in automatic movements, lubricating the barrel walls is essential for the mainspring and the bridle to function properly. The lubrication prevents excessive friction and ensures the mainspring, and the bridle can slip properly.

Lubricating Barrel Walls: Best Practices

Method 1: The 3 Dot Method to Apply Barrel Grease in Automatic Barrel

The first method involves putting three drops of grease spaced out evenly around the barrel walls. While the slipping bridle will distribute the grease evenly around the barrel wall, this method can produce a lot of problems, especially if you don’t have a lot of experience doing it.

3 Dot Barrel Lubrication Method

Issues with Method 1

Firstly, the mainspring has to be fully wound and unwind at least seven times before the lubrication can be completely spread out, which can be a challenge if you’re working on a self-winding only movement.

Secondly, it can be difficult to judge how much of a dot of grease to put on these three locations, as the amount will change depending on the diameter of the barrel and the size of the mainspring. Additionally, the grease can get pushed down into the bottom of the mainspring barrel or cause contamination, which will lower your amplitude.

Method 2: Applying a Light Coat of Grease

My preferred method is just putting a light coat of grease along the barrel wall. The biggest challenge with this method is merely making sure that you keep the grease centered on the barrel wall and don’t get it all over the bottom of the barrel or in the groove that the lid sits in. This is definitely something that you want to take your time doing, but it’s well worth the effort to get it right.

Lubricating Barrel Wall Method #2
Lubricating Barrel Wall Method #2

Installing a New Mainspring

 Orientation and Installation

 When working on a watch, it’s often necessary to install a new mainspring. This is especially important when working on an automatic barrel. To ensure success when installing a new mainspring, it’s important to check the orientation of the spring before proceeding. If you need more information on mainspring select

Using a Mainspring Winder vs Hand Winding

 If you’re planning on reusing the old mainspring, or the new mainspring coil that you got,  is too large to actually fit inside the barrel, you should use a mainspring winder. While it’s possible to install a mainspring by hand, the chances of the mainspring becoming coned and creating a friction problem are pretty high.

However, if you’re new to using a mainspring winder, there’s definitely a learning curve, and you’re probably going to screw up a couple of springs trying to figure it out.

Using a Mainspring Winder

To use a mainspring winder, start by inserting the mainspring into the winding barrel. Make note of the direction that you’re going to be winding the spring into the winder. Then, insert the winding stem into the center coil of the spring. As you wind it, make sure that you keep the lid of the stem tight against the winding barrel itself, otherwise, that spring is going to come popping out.

Installing Mainspring into Winder
Installing Mainspring into Winder

 Installing the Mainspring when Servicing the Automatic Barrel

Once the spring is fully inside the winder, reverse wind until you can feel that the tension has taken off the spring. Then, slowly work your tweezers under the cap as you gently pull the stem out to about an eighth of an inch or so, just enough so that you can get your tweezers inside the winding barrel.

Inserting Tweezers into WInder
Inserting Tweezers into WInder

The first thing you need to make sure of is that the hook has been released from the hole of the inner coil of the mainspring. If it’s not, continue to reverse wind as you’re gently pulling the stem up. Then, using your tweezers, hold the spring down while slowly pulling the stem out of the center of the mainspring. Be very careful while it’s still at the thickest part of the winding stem.

Hold the mainspring down with your tweezers until you can pull the stem all the way out. Then, simply insert it into the barrel, make sure that the barrel’s on a solid surface, and push the mainspring out. By following these steps carefully, you can successfully install a new mainspring in your watch barrel.+

Installing the Arbor and Lid

Using an Arbor Vise Installation when servicing Automatic Barrels

When installing the arbor into the barrel, it’s important to make sure the hook is locked in place at the end of the mainspring. For this process, I prefer to use an arbor vise to hold the arbor while I insert it into the spring.

Although tweezers can be used, they may not be the best choice if the center coil is too tight, as there is a high chance of the arbor flying off into the distance. The arbor vise, on the other hand, is a secure and reliable method that I’ve never had a problem with.

Installing Arbor with Arbor Vise
Installing Arbor with Arbor Vise

Service the Mainspring Barrel: Using a Barrel Closer for Lid Installation

 Once the arbor is installed, the next step is to install the lid. I recommend using a barrel closer to apply even pressure on the barrel lid to secure it in place. Once you hear it snap in, visually inspect the lid to ensure that it’s closed properly.

Barrel Lid Closer
Barrel Lid Closer

Checking Arbor Hook Security

 After the barrel is fully assembled, it’s crucial to check that the arbor hook is secure on the mainspring. This can be done by winding it before it goes into the movement, by holding the barrel in your fingers and turning the arbor with the arbor vise.

Buying Used Mainspring Winders

Mainspring winders are a tool that many new watchmakers avoid due to their expense. When looking to purchase a used mainspring winder on eBay, the biggest problem is finding ones that actually have a hook that can grab the hole in the center of the mainspring.  Worn hooks will not be able to wind up the mainspring in the winding barrel.

Although Chinese mainspring winders may be more affordable, the quality of the hook is questionable and may not withstand the torque required to wind up the mainspring.

For hobbyists, purchasing a half or full set of Bergeron mainspring winders is unnecessary and overkill. Professional watchmakers use these sets because they work on a variety of watches, from tiny ladies watches to big old pocket watches.

Right Hand Winders vs. Left Hand Winders

There seems to be a lot of confusion among watch enthusiasts about mainspring winders, particularly about whether to buy right hand or left hand winders. In this section, we’ll break down the difference between the two and provide some clarity.

Identifying Right Hand and Left Hand Winders

 To determine which winding stem you need, simply turn the mainspring so that the very end of the innermost coil where the hook hole is, is at the 12 o’clock position. If the very tip of the innermost coil is pointing to the right, you’ll need a right hand winder. Conversely, if the tip of the innermost coil is pointing to the left, you’ll need a left hand winder.

Right Hand Winder
Right Hand Winder
Left Hand Wind
Left Hand Wind

Swiss vs. Japanese Movements

Generally, Swiss movements wind clockwise, requiring a right hand winder (Bergeron winder with a red dot). Japanese movements, on the other hand, usually rotate counterclockwise, requiring a left hand winder (Bergeron winder with a blue dot).

Choosing the Right Size Winder

Bergeron Winding Barrel Numbers

 Bergeron winding barrels come in various sizes, and it’s important to choose the right size for your mainspring barrel. The number 5 fits into a 9mm barrel, the number 6 fits into a 10mm barrel, and the number 7 fits into an 11mm barrel. These three sizes cover most average size mainspring barrels. However, for smaller or larger watches, you may need to buy additional sizes.

Measuring a Winding Drum
Measuring a Winding Drum

Cost-Effective Option

 If you’re looking for a cost-effective solution, I recommend purchasing individual winding barrels as you need them. You can purchase a single handle (either blue or red) and the individual size winding barrels, instead of spending a large amount of money on a Bergeron half set or full kit. With just a couple hundred dollars, you can have the best mainspring winder on the market for wristwatches.

Bergeon Winder Selection
Bergeon Winder Selection