ClockInfo.com

I just overhauled an Ansonia oak shelf (kitchen) clock (my job no. 4357). It has the 4 pillar 8 day time and strike movement of dimensions 5 x 3-1/4 inches. The original mainsprings in these clocks are 3/4 inch wide and typically about .0155 inch thick. The previous repairer had installed a time mainspring .0185 inch thick! The loop end of the spring is labeled “USIBEL FRANCE”. I replaced this spring with a new spring that is 3/4 inch wide, .014 inch thick and 108 inches long. The pendulum motion is great (running arc slightly more than twice the escape arc).

I have seen (and discarded) these thick USIBEL FRANCE mainsprings many times before. They were sold by clock parts suppliers such as S. LaRose as “mainsprings for 8 day American Clocks” and sometimes described as the finest mainsprings, made in France. I guess they were fine for many repairers, as they are so strong that they will make a clock work without being correctly repaired! I have measured some of these springs to be as thick as .019 inches! Just by winding the clock, you can feel that they are way too strong. If used for too long, they will cause severe wear to the mainwheel teeth.

The force that a mainspring provides is proportional to the cube of the thickness: .0185 cubed divided by .0155 cubed is 1.7, so the USIBEL spring is providing 1.7 times the force of the original spring (actually it is even worse, as modern steel is better than steel made 100 years ago. So the new .0185 inch thick spring is probably at least twice as strong as necessary.

I used a no. 77.303 from R & M Imports that is specified as 3/4 x .017 x 120 inches. The springs I received have an actual thickness slightly less than .014 inch, and I shortened a spring to 108 inches and re-attached the loop end. This spring seemed so weak when uncoiled that I wondered if it would have enough power! But it works great for the time train, as mentioned in the first paragraph. NOTE TO MYSELF: Next time, leave the spring 120 inches long - there appears to be plenty of room.

Note: R & M has a no. 77.301 mainspring that is specified as 3/4 x .014 x 108 inches that may be German made, and seems stronger than the spring discussed above. I like the 77.303 the best.

It is interesting to compare the force provided by the USIBEL spring to the force provided by the .014 inch thick spring: .0185 cubed divided by .014 cubed is 2.3. This mean that the USIBEL spring provides approximately 2.3 times the force of the .014 inch thick spring. A clock running with the thick spring will wear itself out prematurely!

If you have an heirloom antique American clock that you want to pass down to future generations, make sure your clock repairer does not (or did not) install mainsprings that are too thick. Original mainsprings should be kept in the clock, unless there is a good reason for replacement (broken, too strong, rusted or damaged).

Merritt’s Antiques has the P1496 mainspring in the red, orange and yellow box again! Last week I received 12 of them. I took two springs, measured them to be .0158 inches thick, cleaned and lubricated them, and installed them in a Seth Thomas 89C movement in an Adamantine mantel clock (my job no. 4396). These springs are perfect for this type of clock. The pendulum motion is good but not excessive.

I just overhauled a Seth Thomas 89C movement for an Adamantine mantel clock (my job no.4401). Both the time and strike mainwheels had significant tooth wear. The mainsprings had the ST logo and may be original, and the thicknesses were .071 for the time spring and .073 for the strike spring. To reduce future wear, I replaced both spring with the Merritt’s P1496 mainsprings, measuring .0155 inches thick. They provide noticeably less force, yet are plenty strong enough to run the clock, provided that the movement has the pivots polished and necessary bushings installed. See this post for information on these mainsprings.

Note 9-11-07: The strike train must be almost perfect to run reliably with this thin of a mainspring. My customer brought the clock back into the about shop two weeks after he had picked it up, saying that it did not always strike. I first established that the mainspring had enough torque by letting the spring down 10 turns from fully wound up (simulating a running time of 10 days).  The striking still ran. I wound it back up, and found that occasionally the strike would not go into warning, and that it was always when gears S3 and S4 were in a specific relationship. I let the mainsprings down, and removed gears S3 and S4. S3 had significant wear on the tooth tips, and there was slight wear on the pinion wires of S4. (With a stronger mainspring, this would not have caused any problem). I reversed the wires in S4 so that S3 would engage with the new portions. Then I removed gear S3 from its hub, turned it over and re-installed it, so that the unused side of the teeth would be employed.

I just repaired a Seth Thomas “Queen Anne” wall clock with time and strike movement. It is a large movement (about 7 1/2 inches tall), much larger and heavier than the standard American movement. In Tran Duy Ly’s book “Seth Thomas Clocks and Movements”, the movement is listed as #85, and the mainsprings are specified as 3/4 wide by 11 1/2 feet long by .018″ thick. On this clock, a previous repairer had messed up the escape wheel teeth. I trued them using the Webster escape wheel tooth straightener, then topped the teeth slightly in the lathe to bring them all to the same length, then carefully removed the burrs. I tested the movement, and the .018″ mainspring seemed to have WAY more force than needed for the time train. I tested a long thin mainspring intended for 31 day clocks: 3/4 x .015″ x 170″, and it had plenty of power for the time train, but was too weak for the striking (it could barely run the strike train until the mainspring was run down 8 turns, but striking was very slow). Thus, I kept the .018″ mainspring for the striking.

After pivot polishing and bushing, I cleaned and assembled the movement. The escape arc is .62 degrees according to the beat scale, and the running arc (not even fully wound up) is 2.5 degrees. Thus, this thin mainspring has plenty of power for the time train. The strike speed sounds normal with the 0.018″ thick mainspring.

Summary:

Seth Thomas Queen Anne Time and Strike Model:

Time mainspring: 3/4 x 0.015″ x 170″ (length is not critical)

Strike mainspring: 3/4 x .018″ x 130″ (length is not critical)

I received a new batch of P1496 mainsprings (3/4″ x .0165″ X 96″) from Merritt’s antiques. They are made by a different supplier than the ones I wrote about recently. The ones I really like come packaged as follows: Each spring is wrapped in oiled paper, then in a plastic bag, then in a red, yellow and orange box. Six springs are contained in a larger red, yellow and orange box.

The newer springs are each wrapped in a plastic bag, and 10 springs come in a brown box. I have not tried one in a clock yet, but I did measure the thickness of one spring: .016″ which is fine, I prefer that they be thinner than .0165″ rather than thicker. You need to check these springs before use, as there were some in the past (from a different supplier) with inner ends that were too brittle.

Merritt’s has informed me that they expect to have more of the springs in the red, yellow and orange boxes by mid-July.

I just overhauled a Seth Thomas called “The Giant, No. 2″ shown in Tran Duy Ly’s Seth Thomas book as being made ca. 1904. The movement is 8 day time and strike with inside escapement and is labeled 8 1/4 (this movement model was later called no. 89 and was made in several pendulum lengths for mantel and shelf clocks. It came in many variations).

This clock had a pair of original Seth Thomas mainsprings (.0182″ thick strike and .0175″ thick time) that would have been ok to leave in the clock, but I wanted to make it easier to wind and reduce future wear

I installed a pair of Merritt’s Antiques P1496 springs that measured .0162″ thick. The pendulum makes a large motion with this mainspring, indicating plenty of power!