The Curta.org Bulletin Board

[bcarter1234]

I recently acquired a Curta Type II with one known issue and a second that I was not aware of.

It has a bent main shaft. The bend is approximately 15 degrees. The crank rotates smoothly and will function as it should in the upper subtractive position. The bend is sufficient to keep it from going all the way down into the normal additive position. The bottom of the crank hits the top of the clearing lever pivot so I have not been able to test that function.

It appears from some searching that a bent main shaft was common enough for instructions to be printed regarding how to straighten one. I'm inclined to attempt to straighten it. Does anyone have any personal experience in doing so? Do you recommend it?

The second problem will likely cause me to return it. As I mentioned I can so far only test it with the crank in the raised subtractive position. With all the setting knobs in the upper zero position one crank of the handle subtracts 10 from the product rather than subtracting nothing. So for example if I set 140 and do one turn of the crank the machine will subtract 150 instead. If the first setting knob is in any number from 1-9 the result is correct after one crank. Additional turns make matters worse.
Setting of 143
1 turn will subtract 143, correct.
2 turns subtract 396, 110 too much.
3 turns subtract 549, 120 too much.
4 turns subtract 792, 220 too much.
5 turns subtract 1945, 1230 too much.
6 turns subtract 2198, 1340 too much.
This does not sound easily correctable. Let me know if I am wrong.

Thanks in advance for any advice.
_________________
Take care,

Brent

[mwu]

It sounds like the carry levers are not being triggered correctly. Subtraction is handled through addition. One off errors are usually because one digit does not carry to the next making the result one less in that digit than it should be.

One thing to check is to ensure that the upper carriage can seat completely down against the rest of the calculator.

[bcarter1234]

Thanks for the response. It sounds like it needs servicing as opposed to a simple adjustment.
_________________
Take care,

Brent