Date Wheel Replacement
There are many ways that an English Longcase clock can have a calendar feature, I would think the most common is where the calendar aperture is below the centre of the dial. This system uses one intermediate wheel, driven, from the wheel underneath the snail (see later pictures) and it has twice as many teeth as its driver, in other words, it rotates once per day. Fixed to this wheel is a pin or lever, which indexes the date wheel. In the example here, where the calendar dial is in the arch, there are 3 intermediate wheels, which are missing. With this arrangement there is more chance of trial and error, when making replacement wheels, hence this article.
So lets take some measurements and see what is needed, where do we start?
The first thing is to count the teeth in the driver wheel, the wheel under the snail.
These normally have 30 or 31 teeth but my example has 24, it doesn’t matter really, all that is needed is a wheel with double the amount of teeth, mine needs 48.
A good rule of thumb when looking for the diameter of the new wheel is, measure from the outside of the driver wheel to the centre of the post or hole and add 2mm to the radius, 4mm on the total diameter. I noticed on my clock that the drive teeth were quite shallow so I turned the wheel blanks a little smaller than required. I used a No 1 module cutter and cut the 48 teeth, due to the size of the blanks, this produced teeth that were thicker than required, my wheel cutting machine has an eccentric cam that allows the blanks to be rotated slightly and another cut taken around the wheels to thin the teeth.
A trial run showed that the wheels were the correct diameter, so onto making the pipes. I have found that the easiest way of finding the height of the wheel seat is to use washers over the post and place the wheel on top. When the height is found, take a reading and scribe this onto .250 diameter brass bar.
I drilled the pipe the same size as the top end of the post and I also turned the wheel seat at the same setting. After parting off the pipe I used a cutting broach to match the post taper.
I soft soldered the pipes onto the wheels and to keep the clean up to a minimum, I used 2 small pieces of solder under the wheel seat, apply heat and used peg wood to press the pipe down.
The last part of this job is to make the flag or lever that indexes the date wheel. I could have used a taper pin to act as the lever but thought that I would show an alternative that is found in better quality work.
A measurement was taken from the wheel surface to the dial plate, this was .500 inch and while the parts were together I sighted through to the root of the calendar wheel and marked the new wheel with a pencil (see picture No 10). A scrap piece of 1/16th brass plate was found and marked to correspond with 2 1/16th diameter holes drilled in the new wheel. These holes should be placed so as to leave room for the taper pin, which secures the wheel.
The plate was placed in the vice and I used a brass strip to act as a straight edge while filling away the waste metal, the 2 round pins were formed and riveted to the wheel. The flag was tested and I had to file off a small amount to get the action right, the acting part of the flag should be rounded over and there we have it, job done.
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