MX KeyGuard – Parametric Clip-On Keyguard for Logitech MX Mechanical

What it is

A keyguard is the oldest and most widely prescribed keyboard accessibility aid there is: a rigid plate that sits just above the keys with one opening per key. You can rest your whole hand, forearm, stylus or head-pointer on the plate, drag across it, and only the key you push down through an opening registers. Occupational therapists recommend them for tremor (Parkinson's, essential tremor, MS), cerebral palsy, spinal-cord injury, stroke recovery, single-finger and mouth-stick typing, and for anyone whose hand drifts or bumps neighboring keys.

Commercial keyguards cost $80–150, are laser-cut for one specific keyboard, and nobody makes one for the MX Mechanical. This one is free, prints on any bed ≥ 170 × 140 mm, and every dimension is a parameter you can change for one specific person.

How it works

• Clip-on, zero modification. Three tiles rest on the MX Mechanical's own top case via front and rear legs, ribs drop into the two key-block gaps, and a 2 mm skirt wraps the case with short snap lips that tuck under the case's bottom chamfer. No adhesive, no screws, no opening the keyboard. Pull the front edge to pop it off.

• Every opening is 1.5 mm above the keycap and sized 2.2 mm inside the keycap edge (13.5 mm for a 1u key, 5.5 mm walls between keys) with a 0.8 mm finger-friendly flare on the top edge. That leaves the key fully pressable but makes it impossible to hit two keys at once.

• Tactile locators: recessed rings around F, J and numpad 5 so the home row can be found by touch.

• Space bar is bridged in the middle so the plate stays stiff over the widest key (it is still pressable from either side).

• Rear cut-outs keep the USB-C port and power switch fully usable with the guard fitted.

• Tiled with drop-in dovetails. The MX Mechanical is 434 mm wide, so the guard splits into three tiles (150 / 165 / 145 mm wide) that joint with vertical dovetail tabs running the full height of the skirt. The seam through the main block steps between rows so it always runs through the wall between two keys — no key is ever split.

• Fits a Prusa MINI, MK3/MK4/CORE One, Bambu A1 Mini, Ender 3 — all three tiles are ≤ 165 × 136 mm.

Presets (pick the one that fits the person)

All four presets are included as ready-to-print STLs. If none fit exactly, generate your own (below) — it takes 15 seconds.

Make it yours (the parametric part)

Where to get it: download MX_KeyGuard_source.zip from the Other files tab on this page. It contains mx_keyguard.py, mx_layout.py, the render/drawing scripts and a README. Requirements: Python 3.10+, then pip install cadquery shapely.

Everything is generated by mx_keyguard.py (Python, CadQuery + shapely — both pip install-able). The keyboard geometry in mx_layout.py was measured directly from Logitech's official MXMecha_Dummy.step.

python3 mx_keyguard.py --preset finger # the default
python3 mx_keyguard.py --preset finger --inset 3.0 # smaller openings for a child's finger
python3 mx_keyguard.py --preset finger --plate 3.2 # thinner plate (lighter, shorter reach)
python3 mx_keyguard.py --block LWIN CAPS FN3 NUMLOCK # no opening over these keys
python3 mx_keyguard.py --merge UP,LEFT,DOWN,RIGHT # one opening over the arrow cluster
python3 mx_keyguard.py --no-hooks # plain skirt, no snap lips (rests in place)
python3 mx_keyguard.py --tiles 1 # one piece, if you have a 440 mm bed
python3 mx_keyguard.py --list-keys # all 110 key names

Per-key opening sizes, tactile keys, chamfer, clearance, hook depth, tab size and seam positions are all fields of GuardConfig at the top of the script. The key-name map image in the gallery shows which name is which key. Every run exports STEP (editable) + STL for each tile and a full-assembly STEP.

Printing

• Orientation: the *_PRINT.stl files are already flipped — finger surface down on the bed, skirt pointing up. No supports needed: the opening flares are 45° overhangs and the hooks have 45° faces top and bottom. The bed texture becomes the surface your hand rests on.

• Material: PETG recommended (the snap lips flex a little more forgivingly); PLA works fine. A satin/textured sheet gives the nicest touch surface.

• Settings: 0.4 nozzle, 0.2 mm layers, 4 perimeters, 20 % infill, 4 top/bottom layers. Each tile is roughly 70–100 g and 5–7 h.

• High-contrast option: add a filament change at 0.6 mm (Z) — the finger surface prints in one colour, everything else in another, so the openings stand out for low-vision users.

• Tolerance on the dovetails is 0.15 mm per side. If your printer runs tight, a few strokes with a file on the tab; if loose, a drop of CA glue in the joint.

Assembly (2 minutes)

1. Drop the three tiles onto a flat table upside-down (skirt up) and press the dovetail tabs together: Tile 1 into Tile 2, Tile 2 into Tile 3. They only go in vertically, so they cannot slide apart once on the keyboard.

2. Turn the assembled guard over and hook the rear edge over the back of the keyboard first (the rear lips tuck under the rear chamfer).

3. Press the front edge down until the front lips click under the front edge. Check the plate sits on the case with no rock.

4. To remove: lift the front edge with a fingernail under the skirt at one corner.

Bill of materials: filament only — no screws, magnets, inserts or glue required.

Who it helps, concretely

• A person with an intention tremor can rest the heel of their hand on the guard and slide to the key instead of hovering; the wall stops the finger from landing on H when they meant J.

• A single-finger or stylus typist gets a physical "funnel" into each key and can lean on the plate between presses instead of holding the arm up.

• Head-pointer and mouth-stick users get a tip-guide that won't let the stick skate across three keys.

• Blocking Caps Lock / Windows / Lock removes the three keys most often hit by accident during a spasm — the ones that silently change what every following keystroke does.

Designed on Logitech's official MX Mechanical CAD dummy (Printables model 1846004); the generated guard was boolean-intersected with the dummy to confirm zero interference and the exact 1.5 mm keycap clearance shown in the section drawing.