Multi Calculator Kit

[teenix]

I've thought about the home grown case option a lot since soldering together an NP-25 kit last year. There was an injection molding machine at the techshop near me when I visited an open house there and I've considered signing up for classes just so I could churn out some cases and buttons. But I have a full time job and a million other things to do.

Another option I'm looking into: Hand-molded Sugru (see: https://www.amazon.com/Sugru-Mouldable-G...B075XS15RC)

I've experimented with a couple of non-calculator applications but I've thought about using sugrue either for creating negative molds and/or for molding actual buttons and face plates or cases within a suitable mold.
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Yes, it is a bit of a problem.

I imagine access to a 3D printer might help quite a bit.

I'm sure a thin but sturdy keyboard frame could be designed out of a square cross hatch pattern about 5mm or so high and 1 or 2mm wall thickness, with the frame holes where the keys would be. The top surface would be flat and solid and be about 1mm thick.

The key pads could be a simple C shape cut out of the top surface from inside each of the underlying frame holes (Say a 1mm gap all around). Most of the bottom edge would still be connected to the top plate for flexibility. That way if you press the pad it will tilt over and downward. This would then activate the switch sitting just below it with only about 1mm of movement required.

Some extra supports for the key frame would have to be high enough to sit on top of the PCB over the switches and provide places for some mounting posts for small screws from under the PCB. There should be no pressure on the centre area of the keyboard as the switches will take the finger load for each key press.

The key pads will not protrude above the top flat keyboard surface so a simple vinyl overlay could be used for any of the keypads.

I was thinking of 0.3mm thick fridge magnet material or similar. It prints nicely on a suitable inkjet printer or from a printing company and is flexible. If there is a thin strip or two of metal glued under the keyboard frame edges then the label should cling to the surface and be interchangeable easily. The 3D printed key frame could have slightly raised edges to keep the label in place. Holes could also be in the face for the display LEDs and switches with some clear red perspex glued from underneath.

A bit of design work I'm sure, but someone with expertise might be able to help.

I have completed a "garage mockup" of a HP-45 with a real HP-45 next to it for comparison.

It is a bit rough especially around the switches as the overlay is just on paper, but the switches work ok just underneath. The case was just a general purpose ABS plastic case which I cut down. The cable is powering the calculator via the USB port although batteries can be used.

cheers

Tony