A new hobby lamp had to come. Plastic fatigue had occurred in the old one, the hood had broken off and hung gloomily from its two-wire cord. Internet promised to send a new lamp for 15 euros, but left the shipping costs in the middle and could not rule out that the thing would arrive already tired. That’s why I bought a new hobby lamp from Aurora for twice the price.
Once at home the switch did not work, luckily Aurora gave a new lamp without hesitation. Its switch didn’t work either and it’s left that way. Aurora can’t help it either, it’s all Cheap Chinese Crap from those containers in the Suez Canal. Once the button of the switch was stuck with tape, the lamp burned excellently. And light that won’t go out is also light.
More annoying was that the lamp was not easy to put in the right position, while that is exactly what the hobby lamp is all about. Within certain limits, he must allow himself to be pulled into any desired position with the little finger. The question was what was wrong here.
Adjustability was the new thing
Hobby lamps as they are sold today are faithful copies of the ‘Federzugleuchte’ used by the company in the 1950s. Midgard was conceived. Midgard was founded in 1919 by engineer Curt Fischer who made his name with the design of all kinds of adjustable lamps such as the scissor lamp (Scherenlampe) of 1919. Adjustability was, say, the new thing and the adjustable lamps from Midgard were so aesthetic that a great if Walter Gropius of Bauhaus installed them everywhere.
Many of Midgard’s adjustable lamps were rods that mimicked the action of the human arm, including the ball joint of the shoulder, the hinge joint of the elbow, and the great range of motion of the wrist joint. The light bulb was in place of the hand. The old Midgard lamps remained in the desired position thanks to the high friction in the three ‘joints’.
The British car designer George Cawardine, ‘fascinated by the interplay of forces between levers and steel springs’, invented an adjustable lamp in 1932 in which a strong diminished friction in the joints was compensated by the pulling force of four steel springs. To be ‘Anglepoise Lamp’ became a great success. Later Cawardine designed adjustable lamps that resemble Curt Fischer’s ‘Federzug’ and perhaps he was with it even earlier, as he died in 1947. Yet today’s cheap hobby lamps seem to be based solely on Fischer’s design. (Variants shows the nice Wikipedia entry ‘Balanced-arm lamp’.)
The Federzugleuchte consists of two parallelograms of nearly equal size, connected by an isosceles trapezoid. The single bars of previous designs are doubled although, you might say, it didn’t have to be. It benefits the smooth pivoting of the lamp if it is pure parallelograms, but that is often lacking in the Chinese replicas. Then the short sides are not the same length.
Locking down is weird
What the Chinese apparently have not been told is that there are steel springs in the hobby lamp to allow more movement in the hinge points and that it is therefore weird to fix the hinges. What they could have come up with is that the ends of the two parallelograms within the trapezoid should be able to rotate freely from each other.
Well, more interesting is the question of whether the Federzug could do without friction in the pivot points at all. Now that the heavy energy-saving lamps have been replaced by light LED lamps, this is once again conceivable. The upper parallelogram, which actually represents a forearm, lends itself best to an examination. The rotating effect (the ‘torque’) that the combined weight of the LED lamp, fitting and shade exerts on the trapezoid increases as the forearm becomes more horizontal, but at the same time the two steel springs are stretched more (which increases their tensile force). So it could be. The configuration is so confusing that we at AW couldn’t figure it out this week.
It is more understandable than the interplay of forces in the classic letter scale that is illuminated here by the hobby lamp. An Eastern European replica of the ‘Concav’ letter scale that the German Philipp Jakob Maul designed around 1915. It is also known as quadrant weigher. The cast iron of the original design has been replaced by urinal steel in the replica.
Another parallelogram can be discerned, but this parallelogram only prevents the dish from tipping. In essence, the Concav is a balance with unequal arms that are also bent 50 degrees apart. The long arm measures 145mm, the short 35mm. The letter exerts a clockwise torque on the arms, the 80 gram counterweight wants them to be counterclockwise. If it is known that the scale itself weighs 55 grams and that all other weights are negligible, then it can be calculated that a 200 gram letter will push the long arm 49 degrees out of the vertical. It only requires a sine table, but of course you have to know how to decompose forces.
A version of this article also appeared in NRC Handelsblad of 23 October 2021
A version of this article also appeared in NRC in the morning of October 23, 2021
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