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Torsion-bar Ride for Morse-code key?

November 23, 2014

 

I’ve seen and used some slick Morse code keys over the years, and collected several of them. When I read that Steve Roberts, W1SFR, had designed a new straight key based on a torsion bar, however, I scratched my bearded chin. My last exposure to the concept of torsion bars came in junior high school, when I dabbled oh so slightly in auto mechanics.

 

Well, I’m here to tell you that unusual though they may seem for this application, torsion bars work quite well for keys. The result, at least in Steve’s case, is one of the smoothest keys I’ve ever used. It takes a few on-air contacts, or a few minutes with a code-practice oscillator, to get used to it. The hurdle, I suspect,  is mainly psychological: Structurally, the key looks like it’s missing important elements found in typical straight keys, so it must not behave like one.

 

In fact, it’s missing nothing.

 

In place of the traditional spring — either in front of the trunnion for a key like the venerable J-38 or behind it for so-called pump keys — Steve’s key uses a brass rod that spans the rear of the black-granite base. That rod serves as the trunnion as well as the spring.

 

I had to do some homework to remind myself how a torsion bar works. It’s all in the twist. The key’s arm is attached to the bar, held fast by a set screw at the back end of the arm. Press down on the key and the bar twists along its axis; it does not rotate freely. The amount of twist the torsion bar can deliver is determined by the material it is made of — in this case brass — as well as its thickness and length.

 

Within the limits set by the bar itself, the amount of tension can in principle be adjusted by sliding the key’s arm toward or away from the center of the bar. The center of the bar provides the stiffest resistance, which falls off toward either end. In practice, Steve found a sweet spot, then flattened the back of the bar a bit so the arm’s set screw wouldn’t slip when an operator depresses the key. As with any straight key, the gap between contacts is fully adjustable.

 

The approach not only provides smooth action, but for an open key, it’s remarkably quiet — as quiet if not more so than keys with hinged covers hiding their innards.

Oh, did I mention that the key is drop-dead gorgeous?

 

As far as I can tell, the torsion-bar design got an initial, high-profile push on the pages of QST, the American Radio Relay League’s monthly journal. In the December 1982 issue, Thomas Leary, W0VTP, publish a brief description of a single-lever paddle he built based on the torsion-bar concept. He designed it for use with iambic keyers, but the paddle could be wired as a side-swiper, also known as a “cootie.” He included detailed plans for building the paddle. Steve mentions the article as the inspiration for his version of Thomas’s paddle — in addition to the straight key —  in a video he’s posted on his website.

 

My key arrived on Nov. 8, just in time for the Straight Key Century Club’s monthly Weekend Sprintathon — the perfect opportunity to give the key a prolonged test drive. After several hours of heavy use, it became clear that this key would be a keeper!

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