The Curta.org Bulletin Board

[Paul1967]

I have taken delivery of my Type II today, while cosmetically I cannot fault it, functionally it has a problem.

I wonder if this is common and is it likely to be easy to remedy.

Basically it regularly jams half way round the cycle.

I have narrowed the jamming down to when the revolution counter is being decremented.
i.e. doing a subtraction or doing an addition with the reverse lever engaged.

During subtraction it doesn't always jam but I have just noticed something odd on the white numbers.

Reversing lever pushed fully upward: If I set the revolution counter to 1001 then I pull the crank out to do a subtraction, the rotation will feel a bit tight but the revolution counter now reads the following for each successive subtraction

99991000
99980999
99970998
99960997
99950666 then it jammed solid and I didn't want to start again.

Moving the reversing lever will un-jam it every time.

I guess that sequence of numbers is a clue to the problem.

Anyway a few photos of the machine (just quick ones on my phone)

[murff]

Most Curtas are not used for more than 40+ years. So the primary oiled and calibrated mechanics is not working properly...
The only thing you can do is to clean the accessible parts (it's up to your skills how deep you can disassemble - and later assembly the Curta).
Another possibility is that your Curta is jammed by forcing some (not allowed) operation which bent some of the delicate parts...




In your case it could be the slightly displaced position of the little gears (setting gear, reversing gear, double setting gear or tens carry gear) on the transmission shaft.
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[Paul1967]

Thanks for the suggestion.

I noticed that the some of the input sliders were initially stiff which gives a clue to how long it had been since being used.

Anyway I have decided to send it back for a refund. Hopefully that will go ok.

[davhamm]

Whats the serial number so others can be aware their might be an issue.

[murff]

(maybe)

519419
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[Paul1967]

[murff]

OK, the serial number was difficult to read on your last picture...



I would pay (all in excellent state)
- $800 to $1000 for an all black Type 2 Curta
- $700 to $900 for a gray one with metal crank
- and for the later one with plastic crank $600 to $800.

So for a not properly running late Curta I would pay ... maybe $400 to $500
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[davhamm]

Not sure what Currency Murff is quoting in his reply.

Using EBAY number you paid US $1,126.62

I just paid US$937.50 for this one. It is in Amazing condition. The foam on the bottom of the can, does no even have indentations, from the curta. Guessing its spent it's life laying down on a shelf. Came in a anti-oxidizing bag even. Very nice. I feel I got a really good deal on this,

Prices seem to be moving upward on Ebay.

If you can wait, deals show up, but if you want it now, you will pay more. Avoid the french seller on ebay, he is asking way to much. Still amazed to see he does sell some of his from time to time.

[murff]

US$
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[davhamm]

Link didn't show up Here is the link to the one I bought
http://www.ebay.com/itm/Curta-Type-II-Mechanical-Calculator-528671-Near-Mint-Condition-/252328394437

[danbrew]

'ya beat me on that bid by $10. curious if you used something like auction sniper or just put down a high bid?

i ended up buying 518651 for about the same price a few days later.

[mwu]

I know this has already been returned, but from my experience (so far) building my 3D printed Curta, it sounds like the carry operation between the fourth and fifth revolution counter digits is failing to engage the tens bell properly.

There are multiple things that can cause that, but misalignment of the carry gears are a likely cause. That can happen if the tens carry lever in question is misaligned, bent, or even broken. I have dealt with all three of those while building my Curta. Misalignment was the most common for me. If that is what the problem was, your hardware might have been in good shape (potentially minus some dirt as murff suggested) and just needed a tuning.

I think due to variations in friction, spring strength, and other factors, the Curta was designed to have some adjustability in the alignment of the tens carry lever bearings which hold the tens carry levers in place. During assembly the bearings are adjusted to the point where if the lever is in the lowered position the tens bell will lift it enough that the spring takes over and lifts the lever the rest of the way up. If the position of the tens carry lever bearing is too low or too high that reset won't work right and results like this may happen. Also if it is misaligned, the gear may not fully engage the carry tooth and get a partial rotation. If that happens the locking gear above it won't engage the locking ring on the tens bell properly and the whole device could seize.

I spent hours adjusting my 3D printed Curta. Plastic is not as rigid as metal which could have caused some of my difficulty since my levers may flex more. However a real Curta is also 3x smaller so they would be tiny adjustments which may make adjusting a real Curta even harder.

Anyway, since it's already been returned I hope this info is interesting if not helpful.

[Paul1967]

So based on the numbers being produced thats where you think the likely problem is.

It's not returned yet, I have still have it in front of me.

The seller originally offered me a partial refund, if I thought I could repair this myself then I would negotiate with him and keep it.

There is a very good set of photos and some guidance on stripping them down here http://www.vcalc.net/disassy/

I know it's a type I but I presume it's 99% the same.

I have miniature tools and can buy whatever I do not have. I have nice angle poise illuminated magnifier on my work bench.

I am sure I could dismantle to a point an reassemble it. My worry is if I find something I cannot repair.

He is not in a hurry for it back so I have a few days to make up my mind.

I wonder how far I would have to dismantle it to clearly see those parts that may be broken/bent?

[davhamm]

I use Gixen just enter you high bid and forget it. Where did you end up buying from another ebay auction?

[mwu]

You would need to remove the outside layers to see. -- this point: http://www.vcalc.net/disassy/tn_Img_2981-3106.jpg. It might be difficult to see the problem (there are lots of parts) and it might not.

After having said all this, I will now argue the devil's advocate. These are old devices and things can break during disassembly. A guy I know broke the circlip that holds the upper carriage on just getting as far as that picture above. Also, the problem inside may be the result of broken / loose pieces inside that can fall out during disassembly.

None of that would scare me, but I have built most of one and feel pretty comfortable with its mechanics (although it would all be 3x smaller). If it does make you uncomfortable, I suggest continuing the route of returning it.