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Merritt’s Antiques has a new 3/4 inch by 0.0165 inch by 96 inch mainspring for American clocks. It is part no. P-1956, currently selling for $7.00 each individually (quantity discounts are available). It is a higher quality, American made version of their P-1496 that I have blogged about earlier.

I bought one of these springs to test. The quality appears to be excellent. The thickness measured as specified, 0.0165 inches. It is tempered to a nice uniform blue, and is well finished with a nicely made, neatly attached loop end.

It seems to have plenty of power, as the coils open way up when the spring is first uncoiled. It may be too strong for some clocks.

Tomorrow I am going to install it in an Ansonia long drop octagon clock with early type movement.

Many American antique clocks with open (not in a barrel) mainsprings use a “standard” mainspring of 3/4″ wide and approximately 18 thousands of an inch thick. There is a lot of variation in these springs between manufacturers, and across clocks made by the same manufacturer. I will comment more on these variations later.

In general, these clocks will work with thinner mainsprings if the pivots are polished and the necessary bushings installed properly. Also, some of these clocks show severe wear to the mainwheel teeth. Installing a thinner mainspring can reduce future wear.

Merritt’s Antiques has a mainspring specified as 3/4″ x .0165″ x 96″, part number P1496. Some of the springs in the first batch I received were about .0155 inches thick. They provide plenty of power for many 8-day American antique clocks, and have worked perfectly in the following applications so far:

• Ingraham oak kitchen clock, ca. 1880, for both time and strike.
• Ansonia oak kitchen clock, 4 pillar movement, strike side (this spring is also fine for the time side, as the original mainsprings are about the same thickness, in fact, even thinner springs would work).
• Waterbury oak kitchen clock steel plates, brass bushed, time and strike springs (this movement originally had thin mainsprings).
• Ansonia oak kitchen clock, 5 3/4 inch tall 5 pillar movement, time and strike springs
• Ingraham time only store regulator, deadbeat escapement, clock runs 15 days on one winding.

The mainsprings in this batch can be identified by being packaged in red, yellow and orange boxes.

In the Waterbury clock mentioned above (my job no. 4369), the new strike mainspring broke in September 2007. I replaced it with the same type of spring Sept. 28, 2007 (0.0155 inch thick).

About 1880, a fine Ansonia Regulator A, time only with calendar, was purchased for an office. The clock was enjoyed by many descendants of the original owner. It was well maintained, and always gave good service. In the late 1990’s, the clock was taken to a repair shop, and the repairman said he could not fix it! So he installed a chiming battery operated movement! The clock was passed down one generation, and the present owner was horrified at the indignity inflicted upon the clock. She asked me if I could find an original movement to install. I said I would try, but that it would take some looking, as the clock needs an earlier type of movement than is commonly seen.

After searching eBay for four weeks, I saw the exact movement we needed. It even had the original brass calendar hand and the hour hand. I bought it, and found a source for a good reproduction pendulum. A colleague supplied an original type minute hand to me. We had the case touched up, and an old glass painted with “Regulator A”.

I installed a Merritt’s Antiques P-1956 mainspring, as described in this post. This spring is 3/4 inch wide, 0.0165 inch thick, and 96 inches long. It is of excellent quality, and provides the correct amount of power.

I overhauled the movement of this clock recently. One of the teeth on the escape wheel was too short, so I inserted a new tooth.

Both mainsprings are original Seth Thomas mainsprings that measure 0.0165 inch thick. The strike speed is adequate, but I wouldn’t want the mainspring to be much weaker. The pendulum takes a fantastic swing, about three times the escape arc. The time mainspring could be quite a bit weaker and still have plenty of power.

This clock appears similar to the College Series “New York” with a different base and glass. It is also very similar to one of the “Capitol” series with a different base and glass.

My job 4526.

Many 30 hour spring driven American antique shelf clock are operating with mainsprings that are WAY too strong! The original springs are often stronger than necessary, but clock repairers have replaced then with springs that are even stronger!

A nice little (17-3/8 inches tall) Seth Thomas I have now (in for adjustment and to have the minute hand properly fitted) has a replacement time mainspring that is feels very strong when it is being wound, at least twice the force that is needed! The clock ticks very loudly! I am going to recommend to the customer that the movement be overhauled and the spring replaced. Or, if he doesn’t want to have that done, I will explain and write on the bill that the mainspring is way too strong, is causing excessive wear, and the clock should not be operated very often.

Job no. 4525

This great looking clock has the original time and strike mainsprings, and only a small amount of mainwheel tooth wear (about 5%).

T: 3/4 wide x .0172 inch thick

S: 3/4 wide x .0172 inch thick

Label on back of case

The 8 day time and strike movement

Back of movement

My job no. 4501

American antique one day spring driven clocks often have mainsprings much stronger than necessary. This can cause severe wear to the mainwheel teeth. Shown here is a Waterbury walnut case kitchen or shelf clock, ca. 1880. The movement has a patent date of September 22, 1874.

The movement has the original strike mainspring of 1/4 inch wide by 0.019 inches thick. Yes, this spring is very thick, but it is not very “springy” and does not provide much force, so there is NO wear on the mainwheel teeth.

The time spring was a replacement of 1/4 inch wide by 0.0157 inch thick. There is about 30% wear to the time mainwheel teeth. I replaced it with a mainspring 5/16 inch wide by .0125 inch thick by 45 inches long (actual specifications: 8 mm x 0.33 mm x 1150 mm). This spring provides plenty of power, enough for the movement to run about 48 hours on a winding. This spring is part no. PM-CS510 from The PM Company. They have a great online and printed catalog, including hard to find parts for Swiss travel clocks.

My job 4365

The movement is designed to accommodate 5/16 inch wide mainsprings.

As received: the time mainspring was 3/4 inch wide by 0.0175 inch thick, and the strike mainspring was 0.0165 inch thick. There was very bad T4F pivot hole wear. The strike train had virtually no wear.

Showing front time pivot holes 3, 4, and 5 before bushing. Note excessive wear on #4

After the overhaul, (I did no bushings on the strike side), the pendulum motion was excessive, and the striking sounded sluggish. I swapped the time and strike mainsprings, and then the pendulum motion was excellent (could still have been less) and the strike sounded fine. Here are the final values of the mainspring sizes (remember that these are ORIGINAL OLD mainsprings, if they were being replaced, thinner spring should be used):

Time Spring: Original old 3/4 x 0.0165 inch

Strike Spring: Original old 3/4 x 0.0175 inch

The bottom of the clock showing date code “6091L” which means December 1906.

My job no. 4487