FocusBridge | Removable Numpad Keyguard for Logitech MX Mechanical

Give each key a clearer target

FocusBridge is an accessibility prototype for people who can press a key but find it difficult to isolate that press from neighbouring keys. This can include people with reduced finger control or involuntary hand movements, and people using a typing stylus.

The raised guide creates individual openings above the numeric keypad. Its intended purpose is to help direct a finger or stylus towards the selected key while leaving the main typing area uncovered. It does not change the keyboard's switch force or key assignments.

A removable guide, without modifying the keyboard

The keyboard sits in a three-piece tray on six soft pads. Four posts on the right-hand tray support a separate keyguard above the keycaps. A broad side tab provides a place to grip and lift off the guard for cleaning, adjustment or shared use.

The tray and posts support the guide independently of the keys. Assembly requires no glue, screws, magnets or keycap removal. The rear stops are interrupted around the charging-port and power-switch area.

This first version uses a lift-off guide: it is not a locking clip or a load-bearing palm rest. The tray sections have sliding alignment tongues and should remain supported by the desk.

Designed to be adapted

The included Python CAD source exposes parameters for the opening width, guard thickness, peg/socket fit, pad thickness and tray-joint clearance. The measured keypad layout is supplied separately in JSON, and the assembly is also included as STEP.

Version 0.1 includes one guide with 21 openings over the numpad area of the supplied full-size MX Mechanical reference. Standard openings are approximately 14 × 14 mm with rounded corners; longer keys have longer openings. The nominal clearance beneath the guide is approximately 2.1 mm above the highest reference keycap, measured normal to the key plane.

Changing the source allows different opening sizes to be explored without modifying the keyboard. Other keyboard models and layouts need their own geometry and fit checks.

Files and quantities

- 01_tray_left.stl — print 1.

- 02_tray_middle.stl — print 1.

- 03_tray_right.stl — print 1.

- 04_guard.stl — print 1.

- 05_pad_print_6.stl — print 6 in TPU.

- FocusBridge_assembly.step — assembled CAD geometry; not a print layout.

- focusbridge_source.py and key_layout.json — editable source and measured key layout.

Suggested FDM starting settings

These settings have not yet been validated by a physical print.

- Tray and guard: PETG; PLA can be used for an initial fit prototype.

- Soft pads: TPU, approximately 95A, printed solid. Alternatively, use six loose 12 × 12 × 1 mm soft sheet pads.

- 0.4 mm nozzle, 0.2 mm layers, 4 walls, 5 top/bottom layers and 20–30% infill for the rigid parts.

- Import at 100% scale; units are millimetres.

- Use the supplied STL orientations. The tray bases sit on the bed; the guard is supplied upside down with its broad top face on the bed.

- Supports are not intended to be necessary in these orientations; inspect your slicer preview. Use a brim if needed for adhesion.

- Every individual part fits within a 157 × 157 mm footprint, before any brim. A 180 × 180 mm or larger usable print area gives additional room.

Do not scale the complete design to adjust tolerances: that also changes the key spacing. Adjust the source parameters instead.

Assembly

- Remove burrs and check that the sliding tray joints and four peg/socket connections move freely. Do not force tight connections.

- Join the left, middle and right tray sections on a flat desk.

- Place the six soft pads on the tray. Measured from the assembled tray's front-left outer corner, the pad centres are at X = 34.5, 224.5 and 414.5 mm, in two rows at Y = 36 and 116 mm.

- Place the keyboard in the tray with its adjustable feet folded. The supplied dummy model does not include the real underside feet, so confirm that the pads contact suitable areas and that the keyboard does not rock.

- Lower the guard over the four posts until its socket blocks rest on the shoulders. Use the side tab to lift it off again.

- Check alignment, access to the switch and charging cable, and the full movement and release of every covered key. If the keyboard moves enough to misalign the openings, adjust the fit before use.

Keep the assembly on the desk; remove the keyboard before moving the separate tray sections. Do not lean or support body weight on the guide. Its stiffness and supported load have not been physically established.

Compatibility and prototype status

Designed from the supplied mxmecha_dummy.step reference for the full-size Logitech MX Mechanical . Compatibility with MX Mechanical Mini, MX Keys, Craft or every regional key layout is not claimed.

The exported STLs have passed digital checks for closed manifold meshes, positive volume and non-degenerate triangles. CAD checks found no solid intersections between the rigid assembly parts or with the supplied keyboard reference in the intended position.