The Art of Making and Repairing Clock Parts
A clock like any
mechanical device, works best when clean and properly lubricated.
Neglect is rarely the friend of an antique clock. Even with the
best of care, all clocks are subject to wear. In time, every
clock will need repair or replacement of at least some of it's
wear-prone parts.
The most common site of wear in a clock is in it's bushings. These are the holes drilled through the endplates of a clock to accept the pivots on which the gears turn. The following photo shows a badly worn bushing from a 100 year old Connecticut-made clock.
The most common site of wear in a clock is in it's bushings. These are the holes drilled through the endplates of a clock to accept the pivots on which the gears turn. The following photo shows a badly worn bushing from a 100 year old Connecticut-made clock.
An oval bushing (badly worn)
With the
proper tools this repair is quite straightforward to repair. The
damaged hole is enlarged on it's original (pre-wear) center with a
precision drill/reamer. A brass or bronze insert of the proper
outside diameter, hole diameter and thickness is then press fit into
the enlarged hole. The new bushing is reamed and polished to accept the
pivot of the gear with the proper amount of freeplay for correct
operation. If these bushings are allowed to wear too much, the
entire gear may move away from it's corresponding pinion to cause the
movement to skip teeth or jam. Regular checkups, (I
recommend every 3-5 years) will catch this wear before it can lead to
more damage.
On some older clocks, lubricant from the mainspring can get transferred to the teeth of the great wheel (this is the large gear directly adjacent to the mainspring). When this happens, dust is attracted to the teeth of the gear. (NOTE that clock gears are designed to run dry; no lubricant is used on the teeth, only the arbor pivots). Another way that lubricant ends up on the teeth of a gear is when some well-meaning handyman sprays WD40 or some other spray lubricant on the entire movement to fix a clock that will no longer stay running. When lubricant is applied to the teeth of a clock gear, this may temporarily get the clock going again, but very quickly, dust and dirt attaches to the teeth. This will cause the teeth to literally grind themselves away. This always leads to the need for a much more expensive repair; gear or pinion replacement or realignment. If a pinion gear is worn, sometimes it is possible to relocate the large gear in contact with it, sliding it up or down on it's arbor to contact an unworn portion of the pinion. If the large gear is worn too much, often the only solution is wholesale replacement of the gear. On Connecticut-made antique clocks, it is sometimes possible to find a suitable replacement from a "parts" movement, or in rare cases, common gears and pinions are available commercially (particularly for modern German movements).
If gear replacements are unavailable, the last resort is to cut a new gear using a milling machine with special cutters and a dividing head. The dividing head is a geared tool that can precisely measure out equal spacings in degrees. If for example a gear is required that has 100 teeth, the dividing head is set up to reproducibly move a gear blank 1/100th of a revolution in order for the gear cutter to precisely cut out the space between two teeth. The dividing head is then moved another 1/100th of a revolution and the space between the next two teeth is cut. This is repeated until all 100 teeth are formed.
Cutting a gear
For some clock repairs there is no substitute for hand-making a replacement part from scratch. In these cases, especially in the case of very old English and German movements, the tools of the trade are a jeweler's saw and a metalworking file. I have make duplicate parts in many cases using just these two tools in the same way a clockmaker worked 150 years ago. When an old English or pre-Industrial Revolution American movement comes into the shop, and has missing, broken or worn out parts, handmaking replacements is most often the only solution, since the original parts were themselves handmade.
This is the part of clockmaking that I enjoy most and connects me to the original clockmaker. It's like taking a time machine back to an era when clocks were made to special order and a clockmaker worked magic with often sub-standard metals and crude manual tools. Many's the time I've seen a 200+ year old movement with imperfect brass endplates having bubbles and voids in what should ideally be a smooth surface. The marks of the original clockmaker's planishing hammer can sometimes still be seen even with his later efforts to file the brass smooth (planishing is the technique of hardening cast brass by hammering). The compass marks are often still visible in the brass endplates where the original clockmaker laid out the gear pattern. It's like touching history. Along with the honor of handling such old mechanical devices, there comes a responsibility to be as true as possible to the original intent of the clockmaker and to minimize the potential diminishment in the authenticity of the original work. This is a responsibility that I do not take lightly.
On some older clocks, lubricant from the mainspring can get transferred to the teeth of the great wheel (this is the large gear directly adjacent to the mainspring). When this happens, dust is attracted to the teeth of the gear. (NOTE that clock gears are designed to run dry; no lubricant is used on the teeth, only the arbor pivots). Another way that lubricant ends up on the teeth of a gear is when some well-meaning handyman sprays WD40 or some other spray lubricant on the entire movement to fix a clock that will no longer stay running. When lubricant is applied to the teeth of a clock gear, this may temporarily get the clock going again, but very quickly, dust and dirt attaches to the teeth. This will cause the teeth to literally grind themselves away. This always leads to the need for a much more expensive repair; gear or pinion replacement or realignment. If a pinion gear is worn, sometimes it is possible to relocate the large gear in contact with it, sliding it up or down on it's arbor to contact an unworn portion of the pinion. If the large gear is worn too much, often the only solution is wholesale replacement of the gear. On Connecticut-made antique clocks, it is sometimes possible to find a suitable replacement from a "parts" movement, or in rare cases, common gears and pinions are available commercially (particularly for modern German movements).
If gear replacements are unavailable, the last resort is to cut a new gear using a milling machine with special cutters and a dividing head. The dividing head is a geared tool that can precisely measure out equal spacings in degrees. If for example a gear is required that has 100 teeth, the dividing head is set up to reproducibly move a gear blank 1/100th of a revolution in order for the gear cutter to precisely cut out the space between two teeth. The dividing head is then moved another 1/100th of a revolution and the space between the next two teeth is cut. This is repeated until all 100 teeth are formed.
Cutting a gear
For some clock repairs there is no substitute for hand-making a replacement part from scratch. In these cases, especially in the case of very old English and German movements, the tools of the trade are a jeweler's saw and a metalworking file. I have make duplicate parts in many cases using just these two tools in the same way a clockmaker worked 150 years ago. When an old English or pre-Industrial Revolution American movement comes into the shop, and has missing, broken or worn out parts, handmaking replacements is most often the only solution, since the original parts were themselves handmade.
This is the part of clockmaking that I enjoy most and connects me to the original clockmaker. It's like taking a time machine back to an era when clocks were made to special order and a clockmaker worked magic with often sub-standard metals and crude manual tools. Many's the time I've seen a 200+ year old movement with imperfect brass endplates having bubbles and voids in what should ideally be a smooth surface. The marks of the original clockmaker's planishing hammer can sometimes still be seen even with his later efforts to file the brass smooth (planishing is the technique of hardening cast brass by hammering). The compass marks are often still visible in the brass endplates where the original clockmaker laid out the gear pattern. It's like touching history. Along with the honor of handling such old mechanical devices, there comes a responsibility to be as true as possible to the original intent of the clockmaker and to minimize the potential diminishment in the authenticity of the original work. This is a responsibility that I do not take lightly.
