The Curta.org Bulletin Board

[davhamm]

Some are metal some are plastic (anyone have pics of each?) would be interesting to compare. I know somewhere I found a Chart that showed Type 1 and type 2 by serial number which were plastic which were metal.

Also I believe how they were attached some were riveted some screwed on but not sure of which where which.

Part Supply
-- Metal - Very low (maybe endangered) one sold Nov 2015 on Ebay for $60 I believe
-- Plastic - ???
-- Alternatives found / created --- ???

Comments / corrections?

[Pete]

I commissioned a small run of plastic clearing rings - they are indistinguishable from the originals and fit any/all plastic-clearing-ring-equipped machines. I think Murff put a picture up somewhere on his site, I sent him a few as a thank-you for all his advice.

If anyone needs a plastic CR I'll sell you one for $5, sorry to be so grasping but small production runs are startlingly expensive and I doubt I'll ever make back what I paid for them!

Metal ones, on the other hand...I have one spare myself bought years ago on eBay, but no machines requiring it. I'd be worried about the installation, too, I'm no watchmaker, and I would have to send it overseas to get someone else to do it. Frankly if a metal one broke on one of my machines I'd be inclined to make the same repair Contina used to do - replace the pop-up with a solid post and install a plastic CR.
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Cheers, Pete

[davhamm]

You say replace the pop-up What do you mean? I didn't know there was a difference in the plastic and metal levers.

Sounds like the plastic are easy to replace compared to the metal, whats the difference?

Thanks

[Pete]

The metal CR-fitted top carriages have two points of attachment for the CR. One, the pivot point, is a screw (don't turn the screw!) on early models and a rivet in later ones. The CR swivels on that pivot and then, in the metal-CR-fitted top carriage, it clicks into a spring-loaded latch which releases when depressed. This spring-loaded latch takes the form of a pop-up button, the CR notch clicks into it and you depress the button to release the CR. For storage in the canister the CR is unlatched and swivelled back out of the way.

On plastic-CR machines, the latch point has no moving parts, it is simply a solid post a couple of millimetres in diameter (much thicker than the metal latch fitting, which is less than 1mm diameter at the thinnest point). The pivot point is identical to the latch point on plastic-CR machines, too - you could pop it off and fit it backwards if you liked. When the CR is deployed you swivel the CR around the pivot and press-fit it onto the post, it "clicks" on. Obviously this method is inferior in that the CR will, being made of plastic, eventually deform and crack from being forced on and off the post, but I imagine Contina thought providing unlimited plastic CRs would be a hell of a lot cheaper and easier than having to take returns and disassemble/reassemble the top carriage just to replace a broken metal CR. Hence their policy when it came to damaged machines...I have an early BB type 2 with a plastic CR arrangement that is clearly a repair job (plastic crank too, someone dropped it on its head and got it fixed) but FUNCTIONALLY it is fine.

So that's the difference. Issue for us collectors is that if you have a machine with a broken METAL CR, you need to get the posts as well as the plastic CR in order to get your machine back to working order. And you'd need to take it apart, not for the faint of heart. Whereas if you have a broken PLASTIC CR, you just ask me for a replacement with your $5 and click the replacement one on and you're off to the races.
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Cheers, Pete

[murff]

... for comparison:




[ metal ]

to buy a metal clearing ring without the shown parts makes it more or less ... useless.
They are riveted, not screwed!



[ plastic ]


[ 3d-printed by Pete ]
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:: m u r f f
:: curta.li

[davhamm]

AWESOME..
I just learned me a whole bunch. Thanks.

[davhamm]

Found the serial number info.

TYPE 1
- Metal CR up through 58562
- Plastic CR on 74738

Type II
- Metal CR up through 541431
- Plastic CR on 557788

Source ; http://www.vcalc.net/cu.htm

[Pete]

One small note - the ones I had made were prototyped in 3D printing but produced by a CNC router, removing material. Stronger and massively cheaper than a 3D print run.
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Cheers, Pete

[davhamm]

On the metal levers that screw in. What does the screw go into. Is that attached to the top? I am assuming from the warning of do not remove screw that it is not attached and would just fall into the curta?

[murff]

Here the drawings with the details for the cleraring lever:

The lever is mounted with a rivet (10093 ... vernietet).
There are some Curtas with a screw, but as I know you can't remove this screw it from outside - it's locked...
(can't find the source...)




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:: curta.li

[stenella]

On early machines, the screw that attaches the metal clearing ring to the carriage goes into a brass nut on the inside. The screw will just turn and tun and turn ... and if you're unlucky the brass nut will fall off and you are ... screwed
Replacing it is indeed not for the faint of heart, but for the reasonably mechanically adept with the right tools (especially the circlips that hold on the carriage are a pain, and mind the tiny ball bearings that can fall out unexpectedly, always work on a tray!) it is quite doable. It ain't rocket science!

Cris