Hermle clock movements used numbers on the barrels. This number is stamped on the barrel cap and can only be seen sometimes by removing the barrel from the clock. This chart will tell you the size of the mainspring that is contained inside of the barrel.
|Barrel Number||Mainspring Dimensions MM|
|10||17 x .45 x 1490|
|11||17 x .42 x 1500|
|20 & 56||17 x .38 x 1200|
|21 & 50||17 x .40 x 1200|
|31||12 x .34 x 1150|
|32||12 x .42 x 1100|
|33||12 x .32 x 1150|
|40||17 x .38 x 1100|
|41||21 x .40 x 1550|
|42||17 x .40 x 1100|
|52||17 x .42 x 1200|
|54||21 x .42 x 1900|
|55||21 x .45 x 1800|
Removing a barrel and spring
Most often the barrel with the mainspring inside of it can be removed from the clock without disassembly of the clock movements outer plates.
This can be done with a mainspring let down tool, a device that allows you to hold the tension of the mainspring with your fist rather than your precious and fragile fingers. The idea is to put the mainspring let down tool over the square post that the key is to go onto, and then move the "click" out of the way with a flat screwdriver, and slowly allow the mainspring to unwind in your fist as you control the speed of the unwind easily with your whole fist rather then the fingers with a key.
To try this with a key usually ends up being a painful experience on the fingers. You will see the click that with its tension spring that your supposed to hold back, this click is what holds the mainspring to wind in only one direction.
Of course if the mainspring is broken, there usually is no worry as there is not much tension on the mainspring to begin with, but just to be safe on the movement, its best to be sure is in the totally unwound position.
Hole End Mainspring replacement service
Send us your clock barrel and we will swap out the mainspring within that barrel with a new one, and send it back. The price for this service is $75 and includes the cost of the mainspring. When you add this to the cart and check out online, you will be paying for shipping. This shipping charge is your prepayment for the barrel to be shipped back to you.
What we will be doing is removing the broken or worn mainspring from the barrel in a safe way first off. Then measure the spring thickness and width and stretching it out to get the length. Next we will use the chart to get the right spring from the list and then pull that spring from the inventory that is already here with us. The installation of the spring will be done with the special tool called a mainspring winder.
Please send the barrel and the broken spring to Clockworks PO Box 339 Huntington MA 01050 with a copy of your receipt.
If you would like to send in your barrel with the broken mainspring, please order at this link.
Installation Service $75
Assessment of damage
When a hole end mainspring breaks in the barrel the impact may have caused damage in the rest of the gear train. It is possible that the pivots that go into the outer plates have bent or the arbors bent some, its best check on this before finding a mainspring.
If the movement is 25-30 years old, it has lived its life anyway. A new movement would be less trouble, cheaper than a over haul, and would last another 30 years, and easier than the repair process.
If you would like to explore the new movement option rather than replacing the mainspring, Please provide the movement numbers off of the back plate of the movement itself and email this information to [email protected] There is another option also, just send us the clock mainspring barrel and we will swap it out with the correct new mainspring for a fee.
Measuring the Hole End Mainspring
A Hole end mainspring is use when the mainspring is contained in a brass barrel.
What is being measured below is the sizes of the new mainspring to match up to the old one.
The width is measured first and matched up to the width below, then the thickness is measured with a micrometer, then the approximate length.
Match the width first, you can then see what spring is closest in thickness and length that will be closest to the old one.
The diameter column is what the spring will fit best, in the inside diameter of the brass barrel. WARNING: Wear safety glasses and gloves if working with a hole end mainsprings, they can and will be dangerous. If you choose, we have a mainspring replacement service, all you have to do is send us the entire barrel.
- Movements (4)