Mechanical calculators: FACIT NEA

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This machine was manufactured by FACIT in Sweden, in 1946 (see here). I bought it at an online auction site, in April 2019, and my first electrical FACIT. There was no way of knowing if the motor would run, since the seller only said it was completely jammed, and that he didn't have the power cable. In spite of two missing keys and a missing clear acetate window, I bought it anyway, since it was a bargain (less than $25) and due to the fact that photos showed the machine in its reset state, so I believed the seller didn't open it up or anything. Exterior was quite banged up, full of scratches and flaking paint, but nothing serious.

This machine is similar to the TK, and was manufactured at about the same time. According to John Wolff, FACIT's first electrical machines from the 1930s only replaced the crank with a motor. The NEA is more sophisticated than that. Attached to the electrical motor, the machine has a set of mechanisms that replace the rotating crank to the right, and buttons for subtraction, multiplication and division. Clearing the input register is done using the motor (“zero” button to the right), but clearing the accumulator and the counter requires using the levers to the left.

Multiplication is semi-automatic, meaning that the operator has to hold down the multiplication key and wait for the required multiplicand digit to show up in the counter, then moving the carriage left, and repeating the process. Division is fully automatic, though: after the dividend is input and added to the left of the accumulator, the input register is cleared automatically and the divisor can be keyed in and also shifted to the left. Then the division key starts up a mechanical algorithm by which subtractions and carriage moves to the right go on automatically until the remainder is zero or the precision limit is reached.

My TK was my first restoration, in which I found nothing broken, so I expected the same from the NEA. Upon arrival, I cleaned it up a bit, and went through the usual spots where a FACIT locks up. I soon got the clearing levers and the keyboard to work. I also put together a first version of a power cable. Testing the motor, I was able to clear the input and perform adds with the first digits – I dared not making anything more complicated and risk forcing the motor. With patience and observation, I eventually got it working correctly.

However, the NEA and the ESA-0 have a plastic gear early in the power train. None of my manual FACITs have anything like this. The plastic gear is probably meant as a “fuse”, so that if something seriously locks the machine, this gear can break and the rest of the mechanism remains unharmed. In my NEA, one tooth was already missing from this gear, and my efforts soon caused another to break, and then two more, so it's become unusable.

I measured the gear, designed it in SketchUp and had it 3D-printed, with the help of colleagues from the Robotics lab at UFMG. I added 1mm in its thickness to try to make the teeth a bit stronger. The result can be seen in the photos below. The replacement gear, printed using ABS filament, fit perfectly.

(I was told by gear makers that the plastic gear material is called “Celeron”, as the Intel chips).

I'll now design and try to 3D print the missing keys, fix the transparent windows, and probably repaint the case and have the reset levers chrome plated, to make it look new.

Have a mechanical calculator stored somewhere, and want to get rid of it? Send it to me!

1946 FACIT NEA s/n 271545

As purchased

 As purchased

Broken original gear and ABS 3D-printed replacement

 Broken "celeron" gear and 3D-printed gear

New gear in place (SketchUp design here)

 Gear replacement

More about this machine

The evolution of FACIT calculators

Video: a FACIT NEA performing a division

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facit_nea.txt · Last modified: 2019/06/15 10:29 by clodoveu
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