The Curta.org Bulletin Board

[Toshbins]

Hi. I have got myself a beautiful Curta Type 1: 21031.
It is pretty immaculate for a 70 year old (has certainly aged better than me visually) and came with what appears to be the original cardboard box, but is siezed sold. I’ve got the bottom off and the handle and just waiting for some circlip pliers to come before trying to get the carriage off. It won’t move up and down despite the rotating mechanism being in the rest position. None of the sliders, nor the reversing slide move at all. The cogs all look hazy so I suspect they are seized to the shafts.
I have an ultrasonic cleaner, but haven’t got the confidence to dunk the whole Curta in, and am conscious that there are differing opinions as to what to use - water - detergent - petrol (despite the ultrasonic cleaner saying not to use flammable liquids) and the wisdom of dunking the whole thing.
I’ll see how I get on once the pliers have arrived, but I suspect the if the carriage won’t move now, it’s not going to then either.

[Toshbins]

Well, I bit the bullet and just submerged the bottom half of the Curta into the ultrasonic bath, with just water and the cleaner detergent that came with the machine. Each time I did it, just for a few minutes, something else freed off. One by one the bottom pivots from the slider rails came out and then each gear wheel started to free off; enough to get all the slider rails out.
I’m more and more confidant that it’s just all gummed up, and with patience I should get it stripped down.

[Kmcqueen]

Don't continue to turn or force anything. I would look at some teardown guides to familiarize yourself with the basics. You should take off the lower two screws that hols the plate on - slowly slide/remove the lower half of the Curta. I can promise the grease has frozen the sliders and probably hardened into the lower end of the mechanism (preventing the handle from turning....which is possible half turned preventing the upper carriage from moving also)

You can either slowly clean/soak the lower end and the shafts of the sliders with Isopropyl alcohol and a q-tip. Or slowly submerge the Curta in about 1.5 inches of alcohol to just clear the lower end (don't submerge the upper part for now). There's a possibility you will need to really teardown the upper complex part....but start at the bottom and see what happens.

[Kmcqueen]

This teardown is really nice and has fantastic pictures!!
https://www.vcalc.net/CU-Disassembly/index.html

[Toshbins]

Thank you.
Yes, I’ve read through a lot of the posts on this site and found the site you mention too.
I’ve managed to get the majority of the Curta apart and it’s clear that apart from the gears all being gummed to their shafts, the tens mechanisms are all covered in white powdery corrosion.
The only thing I’m nervous of now is taking off any of the little c-clips. Some are less accessible than others and I don’t want to have to make new ones if I break any.
I think I may be ok with stripping everything apart from them, using the water bath and then following the oiling and greasing instructions.
The main thing is that nothing appears bent or broken at all, so I’m hopeful of a good rebuild when I get back from holiday.

[Kmcqueen]

I think I would avoid water. Most of the Curta is moisture safe.....except for a few steel parts like small springs in the setting shaft levers, round ball bearings (the first time I took one apart I had things soaking in a small container of alcohol and evidently there was a bit of water in the bottom....rusted all the ball bearings from the top carriage - had to replace them) and a few other parts. I would stick with alcohol. Once you carefully start removing the tens mechanisms (one at a time) - it's pretty easy to clean, oil and replace. You can clean the tranmission shafts and gears without removing any of the c-clips. A little slow but you can do it!

[Toshbins]

Thank you for the advice. The sliders did get wet in the ultrasonic cleaner, but now that they’re off I’ve oiled them so I hope they’ll be ok. The carriage and counters etc. all look clean and free, so I won’t be putting that in the ultrasonic. I’ll take it apart and reassemble after checking.
The ultrasonic machine has made a great job of the bottom half so I’ll use it for the shafts and gears and maybe the tens sliders, but I can dry them all easily afterwards.
I’ll let you know how I get on.

[Toshbins]

I got a bit overconfident. It was going so well. All the brass gears and the tens sliders were cleaning up well with a little bit of vinegar, so I thought I would take the last few off to be able to get to them better. The first c-clips came off easily, but the then the third one broke as I took it off.
So now I need a new c-clip .
I seem to recall one of you guys making them so I’ll see if I can find the thread, unless I can find a replacement anywhere?

[Toshbins]

Well, I’ve finally finished.
Romano in Italy were very helpful with a useful suggestion for getting around the broken spring clip problem. However I managed to make a new clip by starting with a staple gun staple and filing it down to fit. It isn’t sprung but I bent it around the shaft and it works fine (I just hope I don’t have to take it off again).
There are other pitfalls in the reassembly, but with the useful videos and photos on vcalc I’ve managed it.
All working perfectly.

What do I do now? I suppose I’ll have to start looking for a type 2.