Thursday, May 27, 2010

Pipe Organ Progress Report

A few entries ago we posted news about the pipe organ that I'm presently building in my shop at home, where I built all the exhibits I contribute to Mindport.

Things are moving forward slowly. All 32 pipes are finished and laid out on the floor, more or less in the pattern they will be finally mounted. They'll be spaced out wider than you see them here, and mounted in two tiers, since their tone is affected by anything spaced too close to them.

Presently I'm working on the keyboard. Initially I'd intended to build all the keys from scratch, but after building the first key I thought- there must be a better way. So I went searching on eBay and came up with a set of keys salvaged from an 1888 vintage Weaver Organ, made by a now-defunct company that was originally based in York, PA. The set cost me $50 and will save literally weeks of work. Well worth the investment. Here's a picture of the inscription on one of the keys:

Still, the keyboard is proving to be a challenge. Devising a mounting scheme and installing the keys requires quite a degree of precision in order to get the spacing and alignment even. To add to the challenge, the keys are not perfectly uniform, so they'll need to be fudged a bit by sanding them here and there, and bending the pins that hold them in position once they're all in place.

The keys will be mounted on top of an airtight pressurized box, the "wind chest." Inside will be 32 "flapper valves" connected by thin wires to the ends of the keys. When you press a key, it lifts a small piece of wood from atop a hole leading to a tube, through which the pressurized air then flows to the appropriate pipe. In the photo below, all the white keys are mounted and now it remains to repeat the process with the black ones.

Of course the pressure in the wind chest has to stay constant no matter how many pipes are sounding, otherwise the tones would not be consistent, since the pitch and timbre change slightly according to pressure. Hence a device is necessary to accomplish that end. The air that drives the organ will be supplied by a blower whose output is funneled into a pressure regulator consisting of a diaphragm and a valve. As the pressure in the wind chest decreases with more pipes sounding, the diaphragm actuates a valve allowing more air to be admitted from the blower to compensate.

There's quite a bit to do yet on this project. As with nearly everything I build, the job turns out to be bigger than I anticipated. I'm glad that I opted to keep this instrument of minimal size, with only 32 notes. Once I do 32 of any part I'm grateful not to face another dozen or so. Also, as the notes become lower in pitch, the pipes become so large that they require a lot of expensive maple, not to speak of becoming physically unwieldy to build in my very small workspace. As you go farther up the scale, the pipes require more and more precision in order to arrive at proper pitch. So this is an optimum range for an instrument if it's required to be of manageable size and cost.

It's probably fortunate that previous to starting such projects I keep myself in denial about what will be involved. Otherwise it I might think twice about starting at all!

Kevin Jones

No comments:

Post a Comment

Site Meter