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32-keyless Trumpet Organ

5 Keyframe

The organ's keyframe is a bit of a misnomer, as there are no keys. The term is also used on keyless organs as outwardly it looks the same, and it's used the same. My drawing shows the main parts of the keyframe.

The keyframe houses, on the left, the tracker-bar which reads holes in the music; and music transport rollers driven by belt and pulleys from the turning wheel, on the right. Above the tracker bar is a roller for keeping the music in good contact. This roller was made from a nylon rod, grooved to allow air to escape through the music holes. The transport rollers, fitted with gears to keep them synchronized, were made from wood dowel covered with rubber tube, and sprung together for grip on the music. Silver-steel spindles were fitted to all rollers.

The design of the bridge is a little different from normal, as I wanted it to be kept compact. Normally, the rollers are sprung by long leaf springs pressing down onto the top of the roller bearing blocks which are normally guided vertically within the construction of the bridge. But to save space here I made them as levers pivoted from a central point, and individually sprung by small coil springs around specially-made adjusting screws. These screws protrude from the top of the bridge for adjustment as normal. The drawing does not show the latch, which was formed from a discarded stainless-steel flat spanner.

Another innovation in this keyframe is the adjustable tracker-bar. The bar is made from hexagonal brass rod, with suitable hexagonal location recesses formed into the frame's sides. Allowance was made for the tracker-bar to move laterally for adjustment to the alignment with the music (in cases where the music requires slightly different tracking). A strong spring at the back of the frame pushes the tracker-bar against a hexagon-head adjustment screw mounted at the front of the frame.

Above left: The brass tracker-bar (shown upside-down) is fitted with tubing ends. These were "glued" into position using alcohol-based shellac. Removing a damaged tube in the future will be a simple matter with the application of methylated spirit (denatured alcohol).

Above right: The rubberized transport rollers, fitted with gears purpose-made by Bob Wallington. After the rubber tube was fitted to the wood core it was trimmed on the lathe creating a rough surface for a super grip on the music card not requiring a super-strong spring.

Above left: The two oak beams with their two braces form the basic key-"frame". At the top of the picture are the hinge parts for fitting the bridge; the brass tracker-bar is in the centre, shown with the tracking adjustment spring at the back and adjusting screw at the front. You can also see the hexagonal recess in the back frame beam. The other two small parts are the bearings for the lower transport roller.

Above right: Looking at the keyframe bridge showing the nylon grooved roller on the left and the upper transport roller behind its gear on the right. Also shown are the adjustable springs pressing down on the pivoted lignum-vitae bearing blocks.

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