Sunday, February 26, 2017

Bushing a Piccolo Post

This piccolo came to me for a repad from another music store, and was curiously already disassembled when I received it. Only after starting work did I discover that one of the trill key posts was stripped out, so its pivot screw wouldn't hold in place. I suspect that may be why it was taken apart and aborted before reaching me. Bushing the post was a fairly quick and straightforward job.

First a small piece of brass was turned, faced, drilled, and tapped to make the bushing.

The rib holding the posts was removed from the body, and the offending post was drilled out to receive the bushing.

The brass bushing was tinned - solder was flowed on to it then wiped off - before installing it in the post. Tinning the part leaves a very thin layer of solder bonded to the base metal, so that in this case it could be installed in the post and the parts heated without having to flow any additional solder that might bleed into the screw hole. Once the parts reached the flow temperature of the solder, the bushing would be bonded to the post. 

The bushing is soldered in place. I used a 94/6 tin/silver solder alloy, which is stronger than tin/lead alloys, especially when using such a small amount on a small contact area. The reason for soldering from this end is that it's easier to set the faced end of the bushing to the desired counterbore depth in the post, cut off the excess flush with the edge of the post, and clean up the edge. If done from the other end, the the bushing would have to be counterbored after cutting off the excess.

After soldering and cleanup. The bushed post is the one on the left.

From the other side. This is the side where the point of the screw will come out and engage with the key.

After reinstalling the rib on the body and checking the fit of the screw, it was necessary to counterbore the bushing a little bit more, which is simple when there's already a counterbore established to guide the cutting tool. 
Since the bushing is completely obscured by the key on one side and the screw head on the other, this is a completely invisible repair.