February 13, 1930. The Model Engineer and Practical Electrician.
thickness of the stone so that it rests in a sink slightly below the surface of the plate, and a circular groove is then turned round it and the metal burnished over it by means of a small conical burnisher. Holes so set are said to be rubbed in as opposed to screwed in; in the latter the hole is set in a brass setting and fitted into a hole in the plate and held by the heads of two or three screws screwed into the plate and pressing on to the rim of the setting to hold it in place as is seen in many watches. In jewelling a regulator clock, one of two methods may be adopted, either screwed-in countersunk jewel settings as above, or the holes may be set in collets having a flange. The pivot holes in the plates are opened out for these to fit and the flange is drilled and corresponding holes drilled and tapped in the plate for screws to hold them in position. This is a more simple procedure and is quite satisfactory, but the countersunk holes make a more workmanlike job, especially if the screws are also countersunk. Supposing it is desired to jewel a regulator clock having plates 4 in. thick; the following method may be adopted or it can be modified to suit existing conditions. If the clock is already made and the train run in, the jewel holes must be obtained to fit the existing pivots, if not, the holes may be obtained in manufactured ruby or sapphire seven millimetres in diameter by two millimetres thick, with holes for the smaller pivots No. 50 drill wire gauge or No. 35 for the larger pivots, which carry the second, minute and hour hands. If the pivots have not been made they should be turned and polished to fit the jewel holes and the train run in the brass plates, the pivot holes are then opened out to the size of the settings. To set the holes a length of good brass rod, or, better still, gunmetal rod, is drilled through its centre with No. 2 drill (twist-drill gauge) ; it is then cut up into the number of pieces required, each being 3 in. long. Each piece is fixed to a small brass faceplate—which fits the lathe perfectly true—by heating it and the faceplate in a Bunsen burner or a spirit lamp with a layer of shellac, it is then run true on the lathe by holding a piece of pegwood on the handrest and gently pressing it against the edge of the hole in the brass until the shellac sets. The hole is then enlarged with a small inside tool till the jewel hole fits the cavity and lies a little below the face of the brass. It must be an easy fit and the jewel must not be forced in or it may be cracked. By moistening the sides of the jewel with some shellac dissolved in spirit and replacing it will keep it in its place. A groove is now turned out round the hole to leave a thin wall of brass standing up round it; by applying an agate or steel burnisher this is burnished over the jewel, and, if carefully done, it will be firmly fixed in its setting. If the amount
turned
removed
and
over
cleaned
is excessive,
up with
a
it
can
small
be
hand
graver. When all the required holes are set the plates must be prepared to receive them. For the sizes given two counterbores will be required, one 15/32nd in. diameter and the other 7/16th in. The centre pins of each must be of the same size. The pivot holes in the plate must now be enlarged to the same size as the pin of the
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counterbore ; the plate must be clamped in the drilling machine and a suitable-sized drill for this purpose passed through all the holes. The larger counter bore, 15/32nd in., is fitted in the drilling machine and must run perfectly true. If the drilling machine has a stop enabling the depth of cut to be limited, it must be set so that the counter bore will cut a hole 5/32nd in. deep;
Fig.
Plate
1.—View
of a
of the
Outside
of the Front Movement
Regulator, showing the Disposition the Jewelled Pivot Holes.
of
if this is not available a collar must be fitted to the counter bore to attain the same result. All the holes can now be counter bored to the required depth. It is important to note that it is the under surface of the back plate and the front surface of the front plate which have to face the counter bore in drilling, as the jewel
settings are put in from the outside of each plate. The smaller counter bore is now fitted in the
drilling machine, its pin placed in the hole at
