Double Brunsviga

This is an interesting machine, not least because it is the first machine that I have restored cosmetically beyond the usual cleaning and polishing.  I regard this as a machine that has narrowly avoided being lost to history.

Machines of this type were used for co-ordinate transformations, gunnery calculations, and complex number calculations.  Since obtaining this machine, I managed to locate this Artillery Manual from 1944.  It is noted that the worked examples in the manual (in Chapter 2 specifically reference the Twin Marchant machine then in use in the British Army; however, the examples can be modified to suit the Brunsviga.

Brunsviga Model D13ZK

Double Brunsviga 032

Serial Number: 223277

Date: 1940s ?

Capacity: 10x8x13 + 10x8x13  (But only the right-hand bank has a revolutions counter)

Price paid: £75

The model number indicates (Z) that the revolutions counter has tens (zehn) carry and a combination (K) clearing option – in this case, the right hand lever clears only the revolutions counter, or the revolutions counter and the input registers, depending on the position of the switch on the right hand side of the front plate (position 1 for rev counter, position 2 for rev counter plus input registers).  The lever on the left clears the input registers, and the result registers (accumulators) are cleared independently via the lever to the right of each register.  There is no back transfer facility on this machine.

The switch in the centre of the front plate selects either (left) both rotors rotate in the same direction, or (right) they rotate in opposite directions.  In the central position, the left-hand machine is disconnected, and the right-hand machine operates as a normal 13ZK.

The revolutions counter is unusual (in common with other German made Brunsvigas) in that the number wheels are marked with two sets of numbers; white numbers count positive revolutions, and red numbers count negative revolutions, with the numbers on display automatically selected by the position of the slots in a sliding masking plate.

When any of the registers are partially cleared, red indicators are visible next to the relevant register, and the machine is blocked.  A green indicator shows next to the revolutions counter when it is reset.

Numbers can be entered directly into either of the accumulators by depressing the lever on the front left of the appropriate register and rotating the rubber-tyred wheels below the register.  Or they would if the rubber on some of the wheels hadn’t perished.

Cosmetic Restoration

I have stated elsewhere on this site that I like machines to look used.  However, this can go too far!

The only mechanical restoration involved getting everything moving with WD40 and lubricating oil, while avoiding getting oil on the pinwheels themselves.  The most recalcitrant part was the sprung pin in the main crank which was rusted firmly in place – without moving this, the crank could not be turned at all.  Once this was freed, the machine was found to move quite well.  The carriage was also rusted in place.  Again, plenty of lubricating oil and not so gentle persuasion got it moving again.  Despite decades of neglect, internally the machine is actually in reasonable physical condition.

All of the panels were removed, and the paint removed (if possible) using paint stripper and wire wool. The front panels were made from aluminium, which proved easier to strip then the steel panels.  Where stripping was not possible, the panels were roughened with wire wool and resprayed.

Black acrylic car paint was used to spray everything, and, after allowing time for drying, the recessed numbers and other details were filled with acrylic paint, the excess being wiped off with a damp cloth while the paint was still wet.

The main crank handle and the resetting cranks were rubbed with wet or dry paper (wet, in this case) to remove the rust and peeling chrome plating, as were the strips holding the decimal markers.

While it’s not perfect, it’s a lot better than before.

Before:

Double Brunsviga

Double Brunsviga

Double Brunsviga

After:

Curta 019

Double Brunsviga

Double Brunsviga

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