Iron & Metal - The Making Of a Spring

Sunball Easy Chair

 

Designed by Gunter Ferdinand Ris & Herbert Selldorf in 1969-1972, it was produced by the renowned ceramics manufacturer, Rosenthal of Selb, Germany. Made of fibreglass, aluminum, and steel, the interior has a multicolor Suede upholstery, stereo, swiveling black plastic shelves 5'6" W x 4'11" H (167cm W x 150 cm H). About 30 of the Sunball Chairs were produced, in white, yellow, and other colors at the end of the 1960's and first few years of the 1970's. Designed for outdoor or interior use. Two quarter spherical swiveling sections are hinged on massive counterbalancing clock springs and can be secured open or closed with a manual twisting lock. The Space Age Sunball resembles an astronaut helmet, or Pac Man. The hinges are primarily lathe turned of steel and aluminum. The ball rests on a rotating base. One was recently sold at Sotheby's for 24,500 GBP on Sept. 27, 2007, and another was offered at the Palais Dorotheum auction on Dec. 24, 2009.

 

fabrication of a 5' diameter clock spring

We show the fabrication of a 5" diameter "clock" spring. The steel type must be selected appropriately, then heated and bent in specially designed jigs and fixtures, tempered, and annealed, before final finishing. If there are any mistakes made during the process, the spring will break, or be too weak to do its job. Properly made, the spring will work for a hundred years or more. We show here the making of a matched pair of clock springs used for counterbalancing the lid of a Modern Ball Chair designed Gunter Ferdinand and Herbert Selldorf and manufactured by Rosenthal in Germany in 1968. The Sunball Chair is one of five dozen made.

 

A jig and tooling are made for turning the heated spring steel stock

A jig and tooling are made for turning the heated spring steel stock, 1" wide x 1/4" thick. The beginning must be securely anchored around a solid steel machined core.

 

The spring is repeatedly heated during the process

The spring is repeatedly heated during the process. If not red hot at the right temperature it will develop stress cracks and break. Note the thin spacer stock wound into the steel too. This will be discarded later.

 

The steel must be hot enough to be wound around the core

The steel must be hot enough to be wound around the core.

 

The steel bar with variably spaced bearing

The steel bar with variably spaced bearing provide suitable leverage for the blacksmith to turn the thick steel stock, and sufficient tightness to the coil.

 

The clock spring is removed from the spacer stock

The clock spring is removed from the spacer stock which will be discarded.

 

The steel must be tempered in a special oven

The steel must be tempered in a special oven, at just the right temperature. Too hot or cold, and the spring will be unusable.

 

After tempering, this type of steel is oil quenched

After tempering, this type of steel is oil quenched. The metal clips that hold the spring are critically important to prevent the spring from unwinding in the oven, or warping. That would ruin the spring.

 

The spring, thousands of degrees Fahrenheit

The spring, thousands of degrees Fahrenheit, ignites the oil, quickly quenched and completing the tempering process. After tempering, the spring will be heated at a low level, approximately 800 degrees Fahrenheit and allowed to cool at a controlled rate, to anneal it. Annealing removes brittleness. If not annealed the spring would shatter in use.

 

New springs, together with the tempering jig

New springs, together with the tempering jig. These are still to be polished. Polishing removes microfractures or fissures in the surface, that could travel and cause breakage.

 

New springs, together with the tempering jig

This is the Sunball chair. The 7" diameter springs are concealed behind steel plates.

 



By Peter Triestman

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