The Clock Repairer's Handbook by Laurie Penman

Author:Laurie Penman [Penman, Laurie]
Language: eng
Format: epub
Publisher: Skyhorse Publishing
Published: 2011-03-06T22:00:00+00:00

Hand-cut wheels

Clocks whose gears were cut by hand should have replacement wheels made by the same techniques, in addition to which, if you do not have machinery that can be adapted to gear cutting, the only solution is to cut by hand. It is not a dreadfully skilled business, nor is it a long-winded one when you have polished up your skills.

Make a gear blank with root diameter, pitch diameter and outside diameter scribed on its surface; clear centre-lines across it and a hole cut in the centre for mounting on a collet afterwards (Fig 165). The centre-lines will tell you if any error came about as the bore was drilled and they will also enable the crossings-out to be made neatly. Free-cutting brass, or engraving brass, is best for blanks; obtain it in the hard or half-hard condition.

Take a large sheet of paper, mark a centre and then draw out a large circle four or five times the diameter of the blank. Using compasses or dividers, divide the large circle into as many equal parts as the teeth on the gear. This will be a matter of trial and error, but the error can be reduced considerably by tackling the job in the right way.

First of all draw a line from one side to the other (a diameter). If the count of teeth is to be an even one, the divisions that you determine can be set around the circle from each end of the diameter. Deal with one semicircle at a time and, when the dividing has reached half-way around this, move to the other end of the diameter and begin again there so that the divisions meet at the half-way point; any error when the two sets of divisions meet can be averaged over the last two or three marks. Repeat the method on the other semicircle (Fig 166).

If the count is an odd one, discover the setting for your dividers by trial and error and then straddle the centre-line at one end with a division and proceed as before, using these two points where you used one end of the diameter before. The other end of the diameter forms the other starting point, of course.

For counts divisible by four, it is a help to using drawing instruments to give an accurate quartering first, and for counts divisible by six one can make use of the well-known method of constructing a hexagon — the radius that drew the circle divides the circle into exactly six parts.

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