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Canister Pads and Bumpers

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Joined: 15 Mar 2017
Posts: 10
Location: USA

PostPosted: Mon Mar 20, 2017 11:56 pm    Post subject: Canister Pads and Bumpers Reply with quote

I want to add some new information to my previous post on this subject.
The silicone foam works extremely well. It is exactly the right durometer, thickness, and color to replace the original 3 mm thick gray foam rubber (moosgummi grau) specified in the Type I Curta engineering drawings.

However, I have learned that the original Curta pads were NOT glued in place, but just held in place by friction. This is true for both the top and bottom pads, and for both the Type I and Type II machines. This ONLY applies to metal canisters!!! I know nothing, nothing, about the plastic canisters!

For the Type I metal canister, if you purchase the silicone foam with the acrylic adhesive, cut the foam and its paper liner with a circle cutter to a diameter of 54 mm, and then remove the paper liner on the adhesive. Wipe the acrylic adhesive off with lacquer thinner and a paper towel. Do a good and thorough job. When all of the acrylic adhesive is gone, the surface will have a shiny, non-sticky, surface, and the foam will probably have "curled up" a bit, due to the lacquer thinner.

Place the foam disc in a warm place to let all of the lacquer thinner evaporate, and the foam disc will flatten. Then just place it in the bottom of the canister, shiny side down. It will look and act EXACTLY like the original moosgummi grau (Engineering Drawing 10130) for the Type 1.

Here's the neat part. The original tolerance on the thickness of these pads was 0.5 mm. If you cut two (2) pieces of the acrylic adhesive foam 3 inches square, and then press the two adhesive sides together, you can then cut a 66 mm diameter disc from the composite 6 mm thick foam which is also an almost exact replacement for the Curta Type II pad. It's about 0.5 mm too thick, but within tolerance.

I'll follow up with replacements for the Type I and Type II top pads when the materials arrive tomorrow.

Curt thought of everything. When new, the top and bottom pads (moosgummi and paragummi) were designed to gently "squeeze" the calculator as the canister was screwed closed, firmly but gently suspending the calculator within its canister. The calculator should not rattle within the canister when shaken. The function of the cotton pad on the top was to provide a low friction surface, so that the top crank was ever so slightly biased in the "backwards" direction when the canister top was screwed on (except for the very early canisters, which screwed on in reverse). The "backwards bias" locked the calculator into it's storage condition, preventing the internal parts from rattling around during transport.
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