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Canister pad removal

 
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rq3



Joined: 15 Mar 2017
Posts: 11
Location: USA

PostPosted: Wed Mar 15, 2017 11:30 pm    Post subject: Canister pad removal Reply with quote

I have a Type I that works extremely well, and the storage can still has its original foam pads, both top and bottom.

Is there a recommended method to remove the old bottom pad? It's hard as a rock, and I'd like to replace it with a new grey silicone foam pad.

I'm hesitant to use any thing aggressive, but if anyone has experience with this, I'd love to hear it.
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murff



Joined: 27 Oct 2009
Posts: 592
Location: Switzerland

PostPosted: Thu Mar 16, 2017 8:10 am    Post subject: Reply with quote

Hi rq3...

Metal canister: you can use a solvent - let it soak for an hour - and then remove the brown mass ...

For plastic canisters it becomes more difficult - carefully remove the hard mass with wooden tool (for example from bamboo). Do not use solvents!

As replacement please check also this solution:
https://curta.org/phpBB2/viewtopic.php?t=490
https://curta.org/phpBB2/viewtopic.php?p=924
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rq3



Joined: 15 Mar 2017
Posts: 11
Location: USA

PostPosted: Thu Mar 16, 2017 9:21 pm    Post subject: Reply with quote

[quote="murff"]Hi rq3...

Metal canister: you can use a solvent - let it soak for an hour - and then remove the brown mass ...

For plastic canisters it becomes more difficult - carefully remove the hard mass with wooden tool (for example from bamboo). Do not use solvents!

As replacement please check also this solution:
[url]https://curta.org/phpBB2/viewtopic.php?t=490[/url]
[url]https://curta.org/phpBB2/viewtopic.php?p=924[/url][/quote]

murff, thanks so much for your reply. My canister is metal, and I'm not sure what solvent would be safe to avoid removing the interior finish. Is it paint, or some kind of fused porcelain?
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murff



Joined: 27 Oct 2009
Posts: 592
Location: Switzerland

PostPosted: Thu Mar 16, 2017 9:32 pm    Post subject: Reply with quote

It's polished anodized aluminum - and should be resistant against usual solvent (e.g. a normal brush cleaner)
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rq3



Joined: 15 Mar 2017
Posts: 11
Location: USA

PostPosted: Thu Mar 16, 2017 11:57 pm    Post subject: Reply with quote

[quote="murff"]It's polished anodized aluminum - and should be resistant against usual solvent (e.g. a normal brush cleaner)[/quote]

With the theory of "do no harm", I first soaked the canister in hot water, which softened the pad, but only on its surface. I then filled it with ethyl alcohol, knowing that would not harm a lacquer surface. The pad actually hardened, but the alcohol didn't hurt the finish. I then tried lacquer thinner, which had no affect on either the pad or the finish.

Since the hot water seemed to have the most effect on the pad, and none on the canister, I gently boiled the canister in water for about 30 minutes. All of the pad basically dissolved and floated away, leaving a sticky brown mess on the surface of the water. The pot was easily cleaned, and the canister looks like new, after a gentle wipe with a Magic Eraser.

I'll be replacing the pad with grey silicone sponge from McMaster-Carr. If Curt had access to this, I'm sure he would have used it.
https://www.mcmaster.com/#silicone-sponge/=16sa2as
It's exactly the right color, thickness, and hardness. Plus, it's platinum cured silicone, so it should last forever, and won't emit fumes that might harm the Curta.

I'm still working on the "mushroom" on the top of the canister, since its a two part assembly (rubber and cotton fabric), and my canister doesn't look anything like the original assembly drawings. The drawings show the mushroom as being external to the "post" part of the canister top. Mine is a rubber "plug" inserted into a relatively very tall "tube" in the canister cap, but still has the cotton pad. I'm going to research this a bit before I commit to replacing the original.
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rq3



Joined: 15 Mar 2017
Posts: 11
Location: USA

PostPosted: Sat Mar 18, 2017 11:32 pm    Post subject: Reply with quote

My German is not good, but with the help of Google, and a friend who speaks technical German, we have reviewed the 10130 and 10131 drawings for the Type I Curta.

The large bottom canister pad was made of "grey, foam rubber, 54 mm diameter and 3 mm thick" (moosgummi). It was glued to the bottom of the canister, with an unknown adhesive.

The top canister pad was made of "natural rubber (paragummi), 15 mm diameter and 14 mm thick", with a 10x7 mm declivity to make it more "springy". It had a cotton surface 1.5 mm thick where it contacted the handle of the Curta. The cotton was adhered to the rubber with an unknown adhesive.

In the United States, McMaster-Carr (mcmaster.com) sells almost exact replacement materials, with the benefit that they are more modern and less likely to deteriorate and corrode the calculator:

Bottom Pad: Part Number 1059N368
Top Pad Tube: 5054K571
Top Pad Felt: 8334K15
15 mm Punch: 3418A15

Careful measurement reveals that the calculator itself was gently compressed between the large bottom foam rubber pad, and the small top rubber with its cotton contact surface. They both compressed to keep the calculator "suspended" in the canister.

The large pad is a no brainer. It is self adhesive, and is simply cut to a diameter of 54 mm, and carefully adhered to the bottom of the canister.

The top pad is a small project. The tube is cut to a length of 14 mm. The punch is used to cut a 15 mm diameter disc of felt. The felt is then adhered to the end of the tube, and the tube is filled to half its length with RTV silicone, and allowed to cure. I would recommend AT LEAST 7 days of cure time before using this assembly! The RTV emits acetic acid during cure! This assembly is then inserted into the existing aluminum tube inside the top of the canister. No adhesive is required. It is retained by friction.

The result is a modern replacement based exactly on the original Curta Type 1 drawings, that results in what the factory intended, with the benefit of modern materials and no damage to the original canister or calculator (God forbid!).

Many thanks to murff to steering me in the right direction!

Because of the age of these machines, the rubber compounds were actually...rubber. From trees. After all of these years, the rubber has degraded to the point that it will actually float away if gently boiled in water for half an hour, and will absolutely dissolve in turpentine given time (over night, or over several days). Neither will hurt the black anodized canister surface.

I hope this helps someone, and again I want to express my thanks to murff for steering me in directions I wouldn't have gone otherwise. His input was invaluable!
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rq3



Joined: 15 Mar 2017
Posts: 11
Location: USA

PostPosted: Fri Mar 24, 2017 1:44 am    Post subject: Reply with quote

OK, now I've done this twice. Just received a Type II, with the same "moosgummi grau" pad in the bottom of the cannister. Hard as a rock, and now brown (braun), and certainly not grau (grey).

I gently boiled the canister in water, watching it this time, and after about 5 minutes the old foam rubber (moosgummi) turned grey and soft. It was easily removed in one piece with tweezers. There was little residue left in the canister, confirming that there was no adhesive used originally.

Again, a quick wipe with dish detergent, hot water, and a sponge quickly removed all remaining residue.

On another note, it seems that some of the original white "O" rings are still in good shape, but discolored. A five minute soak in household bleach diluted 50% with hot water removes almost all of the staining. Rub the "O" ring gently with your fingers , and when the staining is gone, drop it into white household vinegar to neutralize the bleach. Rinse in hot water, allow to dry, and apply a light film of DC-4 silicone grease or Krytox grease.
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