The Delacour Boring Machine
for Butts, Hammers etc.

Click on an image to see it at full size

Description:—This machine is designed to perform all precision boring jobs on piano action parts. In practice it is mainly used for the boring of hammer-heads and butts. I built the machine in about 1982.

The height of the drill is adjusted by a wedge under the base block of the motor. The angle of the carriage is adjusted by the small light-coloured knob, whose stainless steel shaft acts as a strong spring to keep the carriage firmly in contact with the base. The tray is pierced with six threaded holes for screwing down a variety of guides or holding attachments adapted to the job in hand. The pictures show two such guides, one for the grand hammer and the other for an old style of upright butt.

The angle of the tray is adjusted by turning the large knob. The stainless steel screw, with a pitch of 1.5 mm moves the transparent wedge 1 mm for every 4 flats of the brass dome-headed nut and, owing to a special curve at the top of the wedge, each millimeter’s movement turns the tray 1 degree, so that a sixth of a turn of the knob (1 flat) changes the angle of the tray 0.25°.

The box attached with 4 screws is designed for the attachment of a vacuum pipe to suck up the drillings as one works. To the top of the box is screwed a sliding stop which is positioned to stop the motion of the carriage at the desired bored depth.

The box and the back block are bushed, piano-fashion, with bushing cloth and the sliding rods, firmly screwed to the carriage, are of polished silver-steel so that the sliding motion is absolutely straight and very smooth.

The hammer-head holder is adjustable at the back with two small protruding screws to bring the centre line of the hammer moulding to the centre line of the tray, so that the drill will pass through the mid-point of the moulding no matter at what angle the hammer is bored. The broad-headed screw at the tail end is adjusted at the beginning of the work so that no movement is possible of the tail from the flat front surface of the holder. The operator pulls the felted end of the hammer-head towards the front of the holder with one hand as he pushes the slide handle with the other. The positioning and removal the hammer-head involves simply putting it there and taking it out; no special clamping is involved. The holder is provided with a slot to allow for changes in bore length from set to set or substantial changes within a single set of hammers. The head of the tail screw allows for minor variations in bore length as are common in most sets of accurately bored hammers.

A practical example:— It is found by measurement that the angle of hammer Nº 29 is 10° and that the strings straighten out progressively until hammer Nº 54, where they continue at 0° to the top. Now 10° is achieved by turning the screw 40 sixths of a turn and we have 25 hammers to bore at an angle, so if the screw is turned one or two flats for each successive hammer, as in the table below, the desired result is achieved. Alternatively, for the extremely fussy, one can equally conveniently turn 1½ turns per hammer, making up the remainder with a few turns of two flats. The scale on the aluminium wedge guide keeps note of the actual degrees. A mark on one of the six flat of the brass nut allows one to know when one full turn has been made.

29 — 036 — 243 — 150 — 2
30 — 237 — 144 — 251 — 1
31 — 238 — 245 — 152 — 2
32 — 239 — 146 — 253 — 2
33 — 140 — 247 — 154 — 2
34 — 241 — 148 — 2
35 — 142 — 249 — 1