K8RA P-4 Iambic Paddle Dust Cover

Overview

A dust cover for the K8RA P-4 brass iambic paddle. The skirt wraps the lower tier of the stepped base, and an inner rim rests on the ledge where the lower and upper tiers meet, so the cover never touches the mechanism or the desk. Four notches let the cover drop over the paddle without disturbing anything: the levers and finger pieces at the front, the adjuster knobs on both sides, and the cord at the rear. The levers stay free, so you can leave the cover on and still send. The callsign and K8RA P4 lettering are flush multicolor inlays, not raised or recessed text.

On the Air

The P-4 is solid brass, and its ball bearings, silver contacts and slip-fit adjusters collect dust fast on an open shack desk. At about five pounds it is not a paddle you put away between sessions, so it needs a cover that can stay on. The knobs and the cord leads at the rear stick out past the base, which is why this cover is notched on all four sides rather than being a plain box. This is the fourth in a set of paddle covers built on the same design, after the W1SFR Fat Boy, W1SFR Blackstone and Kent single lever covers.

Print Settings

- Printer: Bambu Lab with AMS, 0.4 mm nozzle

- Material: PETG-CF for the body (the carbon fill hides layer lines on the large flat faces), plain PETG for the callsign inlay (gold) and the K8RA P4 inlay

- Layer height: 0.20 mm

- Walls, top/bottom layers, infill: Bambu Studio defaults

- Supports: none

- Orientation: upside down, roof on the plate. All four notches open upward in this orientation, and the inner rim has a 45 degree gusset, so nothing needs support. The roof comes out flat and clean for the lettering.

- Print time and filament use: not specified (model volume about 70 cm3; fit ring about 23 cm3)

The 3MF is set up for three filament slots: cover body (1), callsign (2), K8RA P4 (3). If you are not using an AMS, assign all three parts to one filament.

Hardware and Assembly

No hardware required. Lower the cover over the paddle with the tall notch at the front, around the levers. The side notches pass over the adjuster knobs and the rear notch over the cord leads. The rim settles onto the ledge between the two base tiers.

Design Notes

Fitted to a measured P-4 with a lower base of 89 x 101 x 21 mm and an upper base of 75.8 x 91.2 x 12.6 mm, centered. K8RA keys are handmade and options varied over the years (magnetic or spring return, wood or plastic finger pieces), so measure your own key before printing.

- Clearance: 1.5 mm per side around the lower base, 2.0 mm walls, 2.5 mm roof. Outside size is 96.0 x 108.0 x 70.1 mm.

- Rim: 3.0 mm onto the ledge all the way around. The ledge is about 6.6 mm on the sides and 4.9 mm front and rear, so the rim stays about 1.9 mm clear of the upper base at the front and rear.

- Headroom: the interior ceiling is 34 mm above the upper base top, which clears the crossbar, bearing posts and binding posts.

- Notches: flat top with 5 mm corner radii, open at the skirt bottom. Heights are measured from the ledge. Front (levers): 30 mm wide x 42 mm. Sides (knobs): 34 mm wide x 32.6 mm, centered front to back. Rear (cord): 30 mm wide x 27.6 mm.

- The side notches assume the knobs span about 30 mm front to back. The knobs are adjustable, so check that yours stay inside the notch at full extension.

- Skirt: stops level with the bottom of the lower base and covers the base edge completely.

A 28.5 mm tall fit ring is included. It checks the skirt, the rim and the lower part of all four notches for about a third of the filament. Because the notches split the ring into four corner pieces, a 2 mm frame along its top edge holds them together. The frame is open at the rear for the cord. Print the ring first if your key might differ from these measurements.

The OpenSCAD source is included and parametric. Base sizes, notch sizes, clearance and both lines of lettering are variables at the top of the file.

Makes, remixes and fit reports on other K8RA models (P-2, P-5) are welcome.