EEVblog #1332 - Facit Mechanical Calculator

[EEVblog]

Teardown (partial) of a Facit 13 digit mechanical calculator from 1967.

John Wolff's mechanical calculator website: http://www.johnwolff.id.au/calculators/Tech/FacitC1-13/C113.htm

[WN1X]

I love old mechanical calculators and typewriters. I really hope you can find a resource to get your Tacit running again.

[EEVblog]

I love old mechanical calculators and typewriters. I really hope you can find a resource to get your Tacit running again.

It's possible with the info on that guys's page, it's just a metric crap ton of work.

[HwAoRrDk]

Judging by the photos, the info on that site was for a hand-cranked version, right? But then, the model number was identical? Seems odd.

Oh, wait, Dave's is a CA1-13. And has more keys, so not exactly the same as described on Mr Wolff's site.

[bsfeechannel]

Although mechanical calculators ceased to be produced in the seventies, you can find people who kept using them long after that. I acquired three mechanical calculators a few years ago. Two were not working. And the only one that is working belonged to a lawyer and has a maintenance sticker from 2012. Crazy.

[tigrou]

This video might give some insight about how it works :


It's the same as the motorized version (it can perform + - * /) but with less automated steps and the need to crank an handle to get results.


How it works :
TLDR; everything is done as a series of additions.

Addition : input first number, crank the wheel. input second number crank the wheel again.
Eg: 0 + 12 = 12
12 + 450 = 462

The main idea is to use pinwheels which have an adjustable number of teeth (between 0 and 9).
Because each wheel is coupled to a counter, each rotation, they add a number from 0 to 9 to the result.
Those wheels are coupled together by a carry mechanism.

- Subtraction : same but the other way around. just crank the handle reverse way.
- Multiplication : it's done as a series of additions :
let's say you want to multiply 78521 by 32
input 78521
crank the handle two times (2 x 78521)
shift input to the left (785120), crank the handle three times (3 x 785210)
- Division : input dividend. crank the handle. input divisor. crank the handle reverse way to subtract divisor from dividend, until it reach zero or less.
the number of times you spin the handle is the quotient
what is left is the remainder.
Eg: divide 72 by 22
72 - 22 = 50 //1
49 - 22 = 28 //2
26 - 22 = 6   //3
quotient is 3
remainder is 6
proceed with the rest until you reach a quotient equal to 0 or enough precision.

[eti]

Teardown (partial) of a Facit 13 digit mechanical calculator from 1967.

John Wolff's mechanical calculator website: http://www.johnwolff.id.au/calculators/Tech/FacitC1-13/C113.htm

Dave, your video is SO good. One thing, please, don't refer to yourself as "dumb#ss Dave" evebn if you say it in passing, as self-deprecation. You are such an immensely gifted, talented man and so knowledgeable in so many areas, but we can't all have full-strength, in-depth knowledge about everything - but that doesn't make you "dumb#ass Dave" - you are such a blessing to those for whom you spend your life exploring, investigating and informing, I don't think it is right or proper for you to - even jokily - put yourself down, you are an amazing man. 

When we say things like this, even in jest, they can subconsciously sink into our spirit and affect us, and that's not a good thing, and can, sometimes, rub off on others and cause them to feel that way about the gaps in their own skills and talents, too.

Take care mate, thank you

[eti]

I love old mechanical calculators and typewriters. I really hope you can find a resource to get your Tacit running again.

It's possible with the info on that guys's page, it's just a metric crap ton of work.

Maybe he'd repair it for you, for a fee?

[Bud]

"To subtract, turn the handle in the opposite direction"

Brilliant !! How many of you could have guessed ? 

So Dave , in your motorized version, reverse the mains plug to subtract 

[poot36]

Check this video out on a mechanical teletype restoration:

It shows how to clean the mechanical parts with simple green.

[amyk]

Video all of it as you take it apart, every single step, and it will help greatly how to put it back together! I know it would probably not be very suited to an electronics channel, but I think a lot of viewers here would like watching a very long video of that...

[Fungus]

The greatest mechanical calculators were the Curtas - like having that big desktop machine in a handheld.

https://en.wikipedia.org/wiki/Curta

[Dag]

Hi Dave,

I have succesfully restored some Facit calculators, including one CA-13, ie the same model you got. Mine is now in perfect working order and I am happy to try to assist if you want some advice and/or if you want to compare the status of your CA-13 with the one I got.

These devices was well constructed are quite serviceable.

In order to avoid that the user enter additional keys while it is carrying out an operation (that would really be a problem in case of mechanical calculators), it contain mechanics that locks all keys until the current operation is completed. This means that if something goes wrong, the calculator will appear completely stuck and locked until the issue has been resolved and the device is back in ”ready for entry”-state again. The consequence of this is that many times the calculator seem to be completely locked and in worse condition than it (many times) really is.

So my advice for now is that you first disconnect the motor and check the function of the motor, the relay and sparc supressor (the latter two in the tin box). Do not engage the motor connected to the rest of the machine until you fixed things that may have been mechanically stuck. My advice is that you find and fix those things with the motor disconnected and handcrank the machine. In my case I had to replace some of the caps. Then my machine was working again.

Another Facit I restored suffered from several parts being stuck (due to dried out oil and full of dust etc). Once the places that was stuck had been fixed (looots of oil and tweaking of the parts to make them move) it started to work perfecly again.

Good luck and let me know if I can be of any help. Cant promise success but at least hopefully you may be able to find where the problem(s) are.

Hopefully you can get to the point where you can experience the joy of dividing 355 with 113 (approx of pi) and see how the machine step by step walk through the full divison through repeated subtraction and its wonderful automatic underflow management. 🙂

/Dag

[EEVblog]

Thanks. Great to have my suspicion confirmed that the stuck keys were some interlock thing.
Not sure if I'll ever find time to try and restore thing thing though 

[Kuber]

Just think of all those mechanical parts and linkages as if they were logic gates, and the complexity of the circuit.  It's a mechanical logic system...a spring acts as a 'pull-up' resistor might, etc, etc.  I once repaired IBM selectric typewriters - maybe not as complicated as this calculator, but a mechanical marvel nonetheless.