large pull cord knob – große Zugbommel

We needed something to pull on to open the gate of our underground garage in our apartment complex—something that nothing could be hung from, or broken off, and that was sufficiently resistant against vandalism.

This pull cord knob has a major diameter of 7.5cm and is 8.5cm high, it weights approx. 70g when printed out of ASA. Its shape is designed to accomodate various hand mobility problems.
(For comparison: A tennis ball has a diameter of about 6.5–6.9cm and weighs 60g.)

→ ‚Zugbommel’

Print and Assembly Options

1. Print the bell itself, as-is, and make a knot around a wide nut or washer.

2. If you want to print it out of something flexible, use the supplied cord retainer (the “bone”) once or twice for more purchase against the bell’s shape.

3. Optionally use the threaded insert (especially if you print the bell as two pieces) and screw plug.

The M36 screw plug has a TX100 drive, but it’s really meant to be moved with something like a brush handle.

The insert is a tight press-fit, it’s possible you’ll need a mallet.
Its threads are tapered, tightest at the bottom; to prevent the plug from moving out.

Recommended Print Settings

• For the bell, find a compromise between resistance to UV, cleaning chemicals, and surface hardness.
  PPS-CF is probably a bad choice, TPU or PEBA could not survive housekeeping’s “universal cleaner.”

• 0.6 or 0.8mm nozzle for the upper half of the bell are good enough.

• 0.4mm for the M36 threaded insert and screw plug

• scarf seam

• ~10% infill for the bell (I like ‘adaptive cubic’ for a soft bell), 2 walls

• 3× M3 heat set inserts (3.0×5.7 for ISO14580 M3×12mm bolts) are optional if the provided M36 threaded insert itself was a tight enough fit.