The Curta.org Bulletin Board

[lfoggy]

Hi All,
I am new to the world of the Curta having just purchased my first calculator, a type II from 1961. It looks to be in unmarked condition. Even the can has virtually no marks or scratches. I suspect its been sitting unused for a long, long time. The Curta works very well. Probably had more use in the last two weeks than it has had in the last 50 years !
The first thing I noticed was the crank handle was very stiff to turn on the crank arm. I removed the little retaining screw and pulled the handle off the pin and found there to be some thick and sticky congealed oil in there. Cleaned that off and turns freely now. Only other issue I've had is that very occasionally when subtracting, the crank arm gets stuck mid-rotation and needs jiggling to free. I am guessing there is some degraded lubrication in there somewhere, like the oil on the handle. What should I do ? Should the Curta be stripped down to its parts, cleaned in an ultrasonic bath, reassembled and lubricated, like you would do for an old watch or clock? How easy is that to do ?
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Lukas

[Toshbins]

Hi Lucas.
Look back a couple of months and you will see a thread about my first Curta. Mine was seized solid, but thankfully just from degraded lubricant and some corrosion on the brass cogs. I enjoyed the challenge of stripping and cleaning it, but it’s not for the faint hearted. I broke one of the tiny spring steel clips that hold some of the gears in place on the shafts. They are 0.1mm thick and pretty much unobtainable as replacements.
If yours is not too bad inside, you may be able to clean it sufficiently without taking any of those off.
Look at the website vcalc.net for a huge amount of information.

[Ravlen]

I'd be interested in hearing how this goes. I haven't had time to work on my own Curta for quite a while now, but mine does the same thing. Works flawlessly and smoothly on addition, but sometimes seizes up on subtraction and needs gentle "convincing" to finish the rotation.

I've talked about it in https://curta.org/phpBB2/viewtopic.php?t=779, and have completely disassembled it and cleaned it as best I could (it was in bad shape), but it feels like things are somehow not perfectly aligned or something like that. Some small issue that only arises on subtraction...

[lfoggy]

Thank you Toshbins and Ravlen, that's very useful. I make and repair clocks as a hobby so have a workshop full of machine tools and am used to small mechanisms but never worked on anything like a Curta. May take mine apart to have a closer look at it. Having said that, I played with it for a few hours today doing some square root calculations and it didn't get stuck at all during subtraction. I'm thinking that a bit of use has loosened up the sticky grease in there. Still, temptation to look inside may be hard to resist !
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Lukas