Problems with Traditional Gasket Sandwich Isolation MountAs mentioned before, plate misalignment can cause issues in gasket sandwich isolation mount. For there to be isolation, the plate can’t touch the top or bottom case, so there is always a little wiggle room. The plate should be perfectly centered, but this relies on eyeballing the plate location when building.
Take this mounting tab on the Chimera, for example. The yellow plate is centered in relation to the gasket cutout highlighted below in red. But during a build, someone could misalign the plate, as nothing is constraining its movement prior to final assembly, resulting in a build that looks more like this:
Note how the plate is not centered vertically or horizontally, yet still fits into the gap meant for the gasket.
Problems with Common Potential Solutions to this IssueMany designs have added extra alignment pins to help align the plate perfectly, but this suffers from the drawback of breaking pure case to plate isolation. Usually, these pins are made with extremely tight tolerances - maybe a 0.05mm gap between the plate and pin. In practice, though, the plate usually touches the pin. Vibrations from the plate during typing can transfer to the case via these pins, rather than through the dampening poron gaskets, impacting sound.
This is the solution I used on Cerberus - where isolation really wasn’t a goal, as the plate touched the top case anyways. Note how there is a tiny tiny gap between the pin and plate - but in reality, they will almost certainly touch. For mounting styles where isolation is a goal - this isn’t an ideal solution because it breaks isolation.
Other designs change away from poron, and instead use silicone “socks” to provide isolation. The silicone socks make contact with the top case, bottom case, and plate, and essentially lock the plate into position by taking up all available space. In my opinion, while this does help simplify the build process, and make a keyboard easier to build, it does not replicate the sound and feel of the isolation provided by poron. So I didn’t want to fall back on this option.
Our SolutionThe CK980C offers perfectly aligned gasket sandwich isolation mount using poron
without any direct case to plate vibration transfer. We’re able to do this using an extra part.
As in a normal gasket isolation mount, gaskets are attached to the top case in the gasket locations:
Note that we also have top mount screw locations also present on the top case.
Next, the plate is top mounted to the top case:
Then - we add gaskets to our extra piece. These gaskets would go on the bottom case in a more traditional gasket sandwich isolation mount.:
Next, we attach this extra piece to the top case.
In this image, you can see the top mount plate screw as well as the screw to attach the extra part to the top case.
Finally - we remove the screw holding the plate to the top case. The remaining screws only hold the extra part to the top case:
The end result is a plate that is perfectly aligned and fully isolated via poron gaskets.
Essentially, we rely on the top mount plate locations to perfect the plate alignment, then remove the top mount screws so that the poron gaskets can provide their isolation. The case is designed so that the plate will not touch the top case once the gaskets are installed and the top mount screws are removed.
As a result of this, though, the plate will sit at slightly different heights depending on if the plate is gasket isolation mounted or top mounted - but the difference is only 0.1mm, and the case walls are designed to hide any gaps under switches when GMK caps are used regardless of mounting style.
Much thanks to Cipulot and James from AKB for giving me a bunch of feedback on this board!
