Low profile Beamspring project
Posted: 28 May 2019, 00:23
After getting a 3278 last year I wanted a more portable version, while it does fit in my backpack it's not ideal for travelling.
- 1:1 reproduction of the mechanism (excluding the large coil spring)
- No reliance on existing parts
- Low profile (different return mechanism)
- MX/Beam mount (smooth beam/selectric caps are my favorite)
Thoughts on silo beam
I started before I was aware of any reproduction effort, perhaps I'll end up preferring that switch when I get a chance to try it. For me there are a few drawbacks:
- no beam/selectric cap support
- complicated custom PCBs (5 parts per switch?), for capacitive sensing it's just a pin header for the sense board.
- click decoupled from actuation, for linears analog sensing seems nice though.
- The original switch was modelled in FreeCAD 0.17, I'm planning to refine the model.
- Lower profile assembly requires recently released FC 0.18 and a2plus addon. Actuation can be simulated using the included macro.
- Beam keycap is parametric but finicky, top angle and YZ offsets can be adjusted as well as dish shape. The reason for the cuboid cutout is the initial SKCM version I did.
Assembly overview: https://gfycat.com/DazzlingFearlessCapeghostfrog
Initial print demos (enable sound):
Click demo/abuse: https://gfycat.com/ShallowNippyGlobefish
Rear (unevenness is due to the kinked beamspring): https://gfycat.com/RightGlisteningIndianabat
Image gallery: https://imgur.com/a/dX2BbpP
Thoughts/progress on each component
My board was missing a few keycaps which I modelled, 3dprinted and later resin cast. I've done the same for the original housing and slider. So far I've only 3dprinted the low profile version in ABS, after smoothing all sliding surfaces it's not too scratchy and quite robust.
The lower profile housing and slider is based on the original model, with unchanged actuation related dimensions but two smaller coil springs (SKCM orange) positioned in the corners opposite the beam. It's 21.4mm from PCB surface to bottom of keycap, the original is ~36.7mm. I used M2x8mm flat head (laptop) screws for slider>beamspring and housing>plate attachment which seems to work fine.
I currently don't have a housing "lid" but instead use the top plate for alignment/mounting. There are currently only circular plate holes so no routing is required, the two alignment holes eliminate original manual alignment issue.
I'm considering a rigid top mold with inserted threaded/linear rods to increase accuracy and limit wear, the deep pillars of the original housing stretched and eventually ripped the mold. Initial test piece was promising.
I'm also considering dampening, the rubber pieces from dampened SKCM could work for actuation (flyplate up + slider down), landing pads are also an option. PCB/plate could be dampened for the return.
After accidentally kinking it during measurement I neutered a single original slider. I haven't done any further research but spring steel sheet etching might be viable
Flyplate/beamspring attachment hook
Laser cut stainless steel SMT stencils (conveniently the same thickness) could be used for testing, JLCPCB rejected my drawing with 156pcs crammed into the default $6 stencil size due to "too many holes", I'll try fewer on my next PCB order. The bending could be done with a 3dprinted jig.
A resin cast (PU) test piece with metal shavings mixed in triggers consistently. The shape is easy to cast and the volume is just 0.35ml. For consistency a whole-keyboard batch with proper powder can be premixed.
Commonsense controller + custom board.
Lasercut acrylic for testing, likely PCB or metal for final
- Mold for housing/slider
- Look into beamspring etching/other processes
- Order hook sheet (SMT stencil)
- Dampening for both flyplate and slider, possibly PCB/plate surfaces
I'd appreciate any input, particularly on lower force springs or alternative return mechanism.