Hole End Clock Mainspring

About Hole End Mainsprings

The type of springs that are wound in a brass barrel enclosure is known as a Hole End Mainspring.

First, measure the Hole End Mainspring by taking the spring out of the brass clock movement barrel.

Then the mainspring has to come out of the brass barrel in order to measure it. There is no other way to do this task. This sounds easy but carefully read the following text on how to do this safely.

Warning

WARNING: Always wear safety glasses and gloves when working with hole end mainsprings. They can, and will be, extremely dangerous to work on. Removal can be violent so please be cautious and know that springs always store power when it is in a coil for so long.

The spring can be broken, or off the hook from the center, and still have an extreme amount of power in the spring. Of course, it can whack, cut and may even shatter, into pieces. So, severe damage to fingers and eyes is a real possibility so protective gear is mandatory.

Let us do it instead

Clockworks offers a mainspring replacement service so send us the entire barrel and avoid the hassle altogether. We will use special tools to safely remove the spring, measure it, and swap it out for the new one.

Measuring Hole End Mainsprings includes the thickness, the length and also the width. Then a comparison of these measurements to the mainspring chart will show the appropriate spring to install. If sending in the barrel, please leave the mainspring in the barrel.

Do not remove it. This is because we need to know which way the clock mainspring gets wound inside the barrel. If the spring is out of the barrel the direction will not be known. Of course this is important in order to replicate the same direction with the new one.

Measuring Hole End Mainsprings

Measuring is done to get the size of the new mainspring to match up to the old one. Measure the width first, then measure the thickness with a micrometer. Then the final measurement is the approximate length. Take all those numbers and compare them to the chart.

Width

Width of Hole End Mainsprings is done first. Measure this in inches or millimeters with a digital micrometer. Then see which spring matches the best in width to the old one.

Thickness

Once the width of the clock spring is written down and you are in the right location of the chart, continue with the next measurement. The thickness of the Hole End Mainspring is done next.

This measurement can be in inches or millimeters with a digital micrometer. Take this measurement and compare it to the chart along with the width measurement. Then see which spring comes closest to the old spring.

Length

Measuring the length can be the hardest part of this. Close enough is sufficient for this. If the spring is way too short it only means the clock will not run for 8 days.

So more frequent winding will need to be done. It is not easy to uncoil this spring to get the length. What we end up doing is putting one end in a vise and stretching it out with a tape measure. Of course when you let go it snaps back quickly and wildly.

Diameter

This is just the width of the inside of the clock barrel. As we said before, the barrel is what houses the Hole End Mainsprings.

The barrel inside diameter is in the list because it can help determine the size of the spring that can fit into that space.

If there is no match for the Hole end Mainspring

Sometimes there just is no match for a mainspring and another size has to be put in. It’s a tough choice at times what to substitute with in this situation. As far as the width goes it’s best to go with a skinnier one instead of wider. The spring that is too wide will make the barrel cap not go on, or stay on.

The thickness is pretty important to hopefully get right. If it is too thick it will put up a fight getting in the barrel and may not want to go in. If it is too thin it may not run the clock. The length is the duration the clock will run such as 8 days or less if it’s too short.

Hole-End Clock Mainspring replacement-service

Hole-End Mainspring Replacement Service

$120.00

Add to Cart

For a Hole-End Clock Mainspring replacement-service, all you have to do is send clockworks the clock barrel. Once we have the barrel, the old spring will be taken out.

Then it is just a matter of installing the new mainspring. When sending in the mainspring, be please sure to leave the Hole-End clock mainspring within that barrel.

The price for this service is $150 and it includes the cost of the Hole-End mainspring, as well as the shipping to return the barrel and new spring back to you.

What will be done

Clockworks.com will remove the broken, or worn, spring from the container in a safe way. The next step is to measure the thickness and width of the spring. The final measurement requires stretching out the old spring in order to get the length.

Next we will use the mainspring chart for reference so that the correct spring will be put into the barrel. We will then pull that spring from the inventory that is already here with us at Clockworks.

The installation of the spring will be done with a special tool known as mainspring winder. Once the new spring is safely within the barrel, the cap snaps back into place and the mainspring is then on its way back to you.

Please send the barrel with the broken Hole-End clock mainspring to us. Sent it to Clockworks 10 E Main St Rd., Huntington MA 01050. Please send with it a check for $150 and a note with the contact information.

Removing a clock mainspring barrel

Often a clock mainspring barrel can be taken out without disassembling the clock movements outer plates, on Hermle or Kieninger clock movements. The mainspring will also still stay inside the barrel.

Letting down the mainspring power

The mainspring let down tool allows the release of the mainspring with the fist rather than the fingers.

Put the mainspring let down tool over the square post the key goes onto. With a flat screwdriver, move the click out of the way.

The click has a tension spring that needs to be held back. This is what holds the mainspring so that it winds in only one direction. Slowly allow the mainspring to unwind in the fist.

This method lets the control the speed of the unwind with the whole fist rather than the fingers. Unquestionably, doing this with a key will result in a painful experience on the fingers.

Of course, if the mainspring is broken, there usually is no worry since there isn’t much tension to begin with.

After the barrel is out

Once the power has been let down, the next step is to yank out the winding arbor shaft. The clock mainspring barrel should then fall out the side of the movement. After the barrel comes out, you can see the number that is on the barrel end cap.

This will tell what hole end mainspring to order. Locate the mainspring by using the hole end mainspring chart.

Be sure to check the movement for any damage as a result of the mainspring breaking. In particular, inspect the teeth of the gears, as well as the arbor on the next wheel up. This could have consequently been bent.

Hermle mainspring barrel numbers

Mainspring barrel number to size spring