Sunday, May 17, 2015

Mirror Clock Project Part 5 - Weight, Pulleys, Pendulum, & Dial

With the case for the mirror clock mostly finished (Part 4) I now had the task of fitting the movement, and making/modifying all the accompanying parts to go with the clock.


Since this is an entirely custom made (and custom sized) creation, there are very few stock items available that would "look right". One of these parts which you might think would be easy to find are pulleys. Sadly the pulleys available from supply houses basically only cover the most basic styles, with most looking mass produced and much later than the period I'm aiming for (1900s vs 1830s). One of the only suitable pulley choices that would work fairly well without any modifications are standard Banjo clock pulleys. I found that they were a bit too large, so I opted to modify some existing "Seth Thomas Regulator" style pulleys.

First, let's have a look at some good examples of original mirror clock pulleys:

As you can see from the photos, a lot of these pulleys are very plain with flat metal saddles in either steel or brass. These are the pulleys I decided to modify. I would have preferred them without rings in them, but these were the size I wanted, and the motion works wheels on the movement also have rings, so it still matches.

Unfortunately I didn't really take any in-between photos, so I only have the finished product. All I did was remove the existing saddles, knock-out the centre pins, and broach the centre holes to remove the burred texture. Once that was done, I turned two small centres with projecting pins, and cut some brass saddles. The saddles were heated and bent, drilled, filed, hammered in place, and then the projecting pins were filed flat to the saddles. Quite a bit of work for just 2 pulleys, but I think they make a big impact on the overall project since they're very visible once the door is open.


The pendulum on this clock is more or less a standard Banjo pendulum, but shorter, and with a "block" top rather than a keyhole style. As-received, the pendulum top had been fabricated from round stock, so I decided to file it down into a rectangle. Once I had figured out the correct length for the pendulum, I filed a rough cast brass blank for the rating assembly and mounted it to the rod.

I wasn't happy with the threads on the rating "stem" and the brass was so soft that it twisted as I was cutting them. I decided to hack that off completely, and silver-solder a threaded steel stem to the rating assembly. The problem was that cast brass is much too soft and pliable, since it isn't work hardened. I really didn't think the threads would last long, so I opted for steel threads. Below is the completed pendulum with rating assembly. The brass bob is "new old stock".


This clock would need a custom weight to drive it. Both because it was driving a custom movement, and also because it needed to have a custom shape.

This was my very first time casting anything in lead. For years I've been saving lead scraps, fishing weights, and tire weights for use in clock weights. The large old pot below shows most of my current lead stock (about 45 Lbs). The bulk of this scrap comes from old fishing weights that I bought years ago at a yard sale.

If you are thinking about doing any lead casting yourself, please do your research on the subject, and work safely. Molten lead is VERY heavy, and in its liquid form is at least 600F. Work OUTDOORS, wear gloves, and avoid the fumes. I suggest watching several online videos, or reading about it from people who do a lot of bullet casting (there's lots of good info out there including where to look for free lead).

To cast lead weights for clocks, simple wooden boxes can be used, however they can only be used once.

For this particular movement, the driving weight needed to be just over 13Lbs.

When I was unmoulding the weight, I thought the wood had completely melted (burned) and that the weight was deformed, but the odd shape seen below is only from a thin little bit of rough projecting edges.

The top had to be chiseled free.

My original weight was done with a fancy curved top. Any rough edges can easily be shaved down with a coarse file. Note that the weight hook was set into the weight mould before pouring.

The bottom was quite rough.

I was very happy with the weight, and I even formed the hook, and antiqued the lead; not long after this, I discovered that I made a huge mistake. I forgot to allow enough space for the weight to fit around the dial.

This meant that the weight was useless as-is, and I had to re-melt it and cast it again in a new mould. The new mould was made without a fancy top, and with a simple notched corner to allow clearance for the dial. Here is the recast weight:

Note: the hook was placed in the centre, but I had to bend it back a bit so that the weight would hang down properly in the case.

The bottom of the weight turned out a lot nicer on this second casting.

Lead patina was applied and then everything was good to go!

A small side note: Most mirror clocks simply use one pulley, with the weight hanging down below the centre line of the dial (directly off the winding barrel). In those cases, the clocks are also taller than mine, so there's enough space for 8 days drop. In my clock, to get the full 8 days, I needed to have the weight travel vertically as much as possible. I had calculated that I would need about 35" of weight line, which added up to about 20" compounded with a pulley to drive the clock for 7 days. With my two pulleys and a 4 1/2" tall weight, I am able to get just over 8 days running time.

The movement is a custom creation made for me by my good clockmaker friend Jim DuBois from Texas. It is made from a standard "Howard style" Banjo clock movement, and he fabricated new custom plates for it in a "D" style. To accommodate the difference in height for my case, Jim also modified one of the wheels/pinions to give me a 20" pendulum. The movement is mounted through the backboard with two large (custom) machine screws (also made by Jim). The top weight and pulley hooks are simple eye bolts with a small section cut away. The Maltese minute hand is only temporary.

The pine panel for the back of the mirror hasn't been trimmed to size or antiqued yet.

Also, the blocks on the wall are currently keeping the clock from swinging to the right under the weight, since I haven't yet screwed it to the wall.

Dial Blocks

To mount the dial, rough wooden blocks are typically used. These are not really my preferred method for mounting a dial, but all mirror clocks used similar blocks. Original examples usually include the use of 2 or 3 wooden blocks to affix the dial. These can be at 12 o'clock and 6 o'clock, in a T formation, or 3 blocks radiating outwards (roughly equally spaced).

Because of some clearance issues with the hands, the pendulum mounting stub, and other minor annoyances, I decided to dish the dial slightly. Most dials on mirror clocks are flat, but occasionally dials from this period were dished. To dish the dial, I made two wooden forms, which were simply clamped tightly over the dial to gently curve it.

The dial is one of the only "stock items" I used for the clock. It is a regular Banjo clock dial, and I have removed the existing silk-screened numerals.

The dial was fitted with 2 cut tacks (upholstery tacks) and 1 swiveling bottom nail. The dial edge has 3 notches that reference against these 3 points.

More soon.