Wooden clocks are driven, in the main by a single drive weight hung from a cord wrapped around the Drum, and it is this type of drive that we are going to look at in this article.
In the first clock, I ever built I used a piece of granite with a hook screwed into the top, it worked well but did not sit well with the traditional image of a clock. For a long time, my plans just included a simple Brass weight which looked the part but, to be honest, wasn't necessarily very easy for woodworkers to construct, so began a series of designs using fabricated parts and some proprietary items.
Design 1 uses a Plastic Tube with wooden endcaps and a threaded rod with nuts at the top and bottom to hold the whole together. I wanted the weight to be attached to the cord simply but a screw-in hook was not going to work with the threaded rod sticking out the top of the weight. This led to the design shown below that uses a Bowline knot on the end of the cord and a wooden hoop holding the nut inside.
With this Tubular construction, the weight is added to the Tube before it is fully assembled. My favourite weight type is of course Lead as it is the densest material that you can practically use and it comes either as Lead shot or as cylindrical weights of the type generally used for Sash type windows.
An alternative to Lead is to use Ball bearings, if bought in the form of 'Catapult shot' they will be much cheaper.
I struggled for a while to find the correct type of Knot to use to hook up the weight to the clock. The problem was that all the knots I was trying would slip until I came across the Bowline knot which is shown here, a bit more complicated to tie but once done it works a treat with no slippage.
Design 2 simplifies the design so that the construction can use a simple hook to connect to the cord hanging from the Drum.
The same weight type can be used as in the previous design but the construction is slightly different in that the top and bottom end plugs are screwed to the Tube around the periphery as shown above.
To make this design even more flexible you can cut a large hole in the Top End plug so that Lead shot can be poured in or out to adjust the weight.
I have the tube shown with a Brass colouring in the above illustrations, you can achieve this by spraying the colour to the inside of the tube before assembly or wrap a self-adhesive Gold film around the outside to achieve the effect.
Design 3 goes for a really simple solution using a standard bottle to hold either Lead shot or Ball bearings or even water depending on your weight requirements.
The illustration above shows how this works using a 500 ml bottle with a Ø28 mm neck, the Hanger showed here cut from plywood sits over the neck and beneath the Cap and the Loop in the Cord formed using the Bowline Knot slips over the bottleneck and then around and to the front of the hanger to engage in the two notches. This simple attachment allows the bottle to be hung on the cord simply and neatly.
I have used this little part numerous times when building prototypes as it allows for the easiest way to adjust the weight to get the clock running regularly without overloading it and putting too much strain on the parts.
Design 4 uses a similar approach with cans, if you own a 3D printer then you can print this Cap adapter to be fitted to the top of a can so that you can use it as a weight on your clock. Click here for a link to the STL file
Design 5 uses a very simple brass weight which consists of a section of Ø24mm brass bar with a length calculated to give you the weight that you need. In the end, I liked this solution best as it was so simple and the small diameter bar give extra clearance from the pendulum Bob which is necessary for some of the clock designs.
To attach the weight to the cord, form a loop at the end of the cord using a Bowline knot and then push the loop in the short hole at the end of the weight. Fit the short weight pin through the cross hole and through the loop and then let the cord take the weight.
The calculation for the length of the bar is as follows:-
Length L = Weight W/π x Radius r ² x 8.5 where 8.5 is the density of Brass in grams per cubic centre meter.
L = 500/π x 1.2²x 8.5 =12.9 cms ( I rounded it up to 13.5cm to allow for the hole drilled in the top.
Design 6 This is a variation of Design 2 where a single Pulley is incorporate to double the running time. The cord is passed beneath a Pully fixed to the top of the weight and the end anchored to the hook fixed into the clock frame. The only disadvantage to this is that you have to double the size of the weight as half of the weight is effectively lost as it goes into pulling on the Clocks framework.
