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Chapter 2—The Frame

The frame of a clock will generally be made of two flat plates joined together at or near the corners with pillars. All parts are usually made of brass except in exceptional cases where we might get a steel frame fitted with bushes. The plates are sawn and filed to size, and, after ensuring they are flat and square, they should be held firmly together with clamps, preferably the toolmakers’ type, while two or three small holes are drilled through somewhere near the corners. These holes are to accept pins or rivets that are used to ensure the plates do not separate during operations; once the pins and rivets are in place, the clamps can be removed.

The next task is to mark the position of the pillars that join the plates together and drill the holes for them; we will come to how they can be fitted shortly. Occasionally clock designs do not have this type of plate; instead they are made with strips of brass, more often than not cut into fancy shapes, and instead of four pillars there are only two, one at each end. The principle of joining them together and drilling the pillar holes remains exactly the same, however. As building progresses, other differences will emerge. For example, there will not be a pendulum, so they will not be fitted with a back cock.

Four basic pillars. There are several ways of securing them and, in this instance, locating lugs have been machined on the ends, which are tapped to accept screws.

The Pillars

Generally speaking, the pillars, or spacers as the layman would call them, will consist of brass bars that may or may not be shaped. Shaping is a matter for the individual builder and, in a limited way, is the opportunity for him or her to express him or herself. Fitting the pillars to the frame is done in several ways: some are hollow and a stud is pushed right through and the parts held secure with a nut, or perhaps the ends of the pillars are machined down and threaded to accept a nut. In other cases they are drilled and tapped and screws passed through the frames into them. A third alternative is to machine a step in the pillar ends and pass this through the holes in the frames, which are then secured with a taper pin, fitted in a hole drilled across the step. One thing that is common to all these methods is that, when assembled, the frames must be rigid and square.

The two plates held together with the four pillars and with the barrel fitted for test purposes.

Pillars should generally be made of brass, unless another material is considered more suitable. The securing threads can be external for use with nuts, or internal for screws. The shape is only limited by the constructor’s imagination; some suggestions are shown above.

Setting Out the Train

The most common way of setting out the train is to scribe a straight line lengthwise down the plates and to set the escapement, center or hour wheel, and the great wheel and barrel along this. The third wheel has to be set at one side in order to allow the pinions and wheels to mesh. Just occasionally we come across another design where the escapement and hour wheel are in line and both the third wheel and barrel offset. This is very rare and any details required for such an arrangement would be available from the drawing and any instructions that might go along with it.

Marking Out

Sometimes clock plans will give measurements showing where pivot holes will be placed; if not, it will be necessary to work out spacing for oneself. Start by lightly dot punching a suitable place for the great wheel on the centerline. Use a depthing tool to mark out a position on the line of the minute wheel; this means meshing the great wheel pinion with the minute wheel so they run very smoothly and without any binding. When satisfied with the meshing, use the tool to make a second mark on the line that has been marked on the plate.

A homemade depthing tool with a number of spare spindles. The design of the tool is similar to the commercial models and requires the use of a heavy spring.

Depthing Tool

A depthing tool is something that some people will not have come across before; it is a tool for setting out gears to ensure that they run smoothly. They can be bought, but for normal purposes a homemade device will do just as well, those that are purchased being far more sophisticated than necessary for occasional clockmaking purposes. The tool is simply a means of meshing wheels and pinions, or two wheels, or the escape wheel and pallets, so that a check can be made to ensure they run properly. A professionally made tool will be spring-loaded and fully adjustable, but good results can be obtained from a simple device consisting of two lengths of bar that swivel together with two holes to accept punches. The punches are the same diameter as the wheel arbors, and so the wheel and pinion are simply slipped on and adjusted. If different-sized arbors are likely to be used, fit brass bushes that can be interchangeable. One of the punches is set in the mark already made and the other is lined up on the line on the plate. A slight tap with a small hammer and the correct place for the arbor of the hour wheel is marked. John Wilding, who is one of the finest clockmakers in Britain, recommends a piece of slotted bar for the same purpose, an idea that works very well.

The back cock must be absolutely square, otherwise the pendulum cannot operate properly.

The depthing tool being used to assemble a plexiglass (Perspex) wheel and a pinion. The tool is adjusted until they are running freely and then it is locked in position. The tool is placed on end, and a smart tap with a hammer on each spindle leaves indents at the correct spacing ready for drilling. As well as obtaining the distances for wheels, the tool can also be used to check the working of the escapement.

A much simpler depthing tool consisting of two pieces of strip steel fitted together with a screw. The spindles are the right size for the wheels, and when they are slipped in place, the necessary adjustments are made. The spindles act as punches to locate the hole positions in the plates.

The tool is now used to set the distance of the third wheel, which cannot be sited on the line because it would then be impossible to mesh all the wheels properly. There is no specific angle at which to set the third wheel and this, plus whether it should be set to the right or left of the line, is a matter of individual taste. Generally speaking, an angle of about forty-five degrees is used; whatever happens, make a note of the angle just in case it needs to be referred to later. Having decided where the wheel will be going, repeat the operation with the depthing tool so that a mark is made for the third wheel pivot hole. From there the tool is used to lay out the distance from the third wheel to the escape wheel, and exactly the same procedure is used. The mark should be made on the line used by the great wheel and minute wheel, and that is the clock train marked out. Holes for the pivots can be drilled, but don’t forget they should be drilled undersize. When the plates are separated, they can be opened out with a taper reamer so they are a nice running fit with the pivots.

There is still one more operation required in order to make all the pivot holes, because the pallets of the escapement also need to be set. The pallets and the escape wheel are mounted in the depthing tool and adjusted until they work smoothly in the same way as before.

Makeup of the plates, showing typical position of pillars and back cock.

The plates are now complete, except that if the clock is to use a pendulum, a back cock must be fitted. This is a bracket that supports the suspension for the pendulum, which can be fabricated or milled from a solid block of brass. It takes the form of a bridge to clear the pallet arbor, the pivot of which locates in a hole in the cock, the suspension being fitted on the arbor between the plate and the bearing. It is essential for the good running of the clock that the cock is secured firmly to the plate and will not work loose. It is also essential that the escape wheel arbor when fitted to the cock is at ninety degrees to the plates.

Some people like to fret out the plates to make an attractive pattern, and this is a matter of individual taste. The fretting will obviously need to be done with the plates secured together. One way of doing this is to draw a suitable pattern on paper, taking care to avoid all pivot holes, cut out the pattern, stick it on the plates, and cut around it. Do not try and chain drill, but drill a couple of holes in strategic places, and use a piercing saw or a power-operated scroll saw, if one is available, to complete the job. Finally, clean the edges of the cuts using small files.

The back cock in position and the crutch temporarily in place.

Something rather unusual in back cock construction, consisting of four spacers and a plate, which is bushed to accept the escape wheel arbor as the plates, in this instance, are made of steel.

The plates in position and the movement assembled.