Neater Pressure Box Catch

by Melvyn Wright

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Neat Pressure Box Catch
Rather than have a catch on top of the pressure box, pressing down on top of the lid, I decided to make it like an organ key frame.  These consist of a catch with a hole in it that engages with a pin in the edge of the key frame lid.

The catch was made from a suitable strip of mild steel, about 1/2" wide and 1/16" thick, bent to shape at the top as shown in the photos.  I fixed it to the front wall of the pressure box with two M4 screws which screw into a tapped plate inside the pressure box (the tapped plate is shown in the first photo).  The holes in the pressure box are slotted, so that the whole assembly can be moved up and down for adjustment.  Nuts and washers could be used here instead of the tapped plate, but it would be more fiddly to adjust, and care would have to be taken to ensure there were no leaks.

The catch engages with a pin protruding from the edge of the pressure box lid.  This consists of a sawn-off nail about 2mm diameter and sticking out about 4mm.  The hole in the catch is oversize, to facilitate easy engagement.

To adjust: close the pressure box lid, push the catch down to compress the seal by the required amount, then tighten the screws.

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