One loop, two different jobs

The bobbin supplies material. Its felt brake resists rotation. The moving pulley stores spare length and, with a known weight, provides a reference tension. Follow the amber thread from the package, over the fixed pulley, down around the dancer and up through the ceramic output eye.

T_dancer = mg / 2    T_brake = τ / r

Two vertical legs support the moving mass, so each carries half its weight in the frictionless, stationary limit. With 40 g total moving mass that is 0.196 N. A constant 2 N·mm brake torque needs 0.182 N at an 11 mm package radius, but 0.385 N at 5.2 mm. The values here are inputs, not measurements of this printed assembly. Rod friction, bearing drag, starting friction and acceleration change the real result.

A fixed felt brake and a dancer do not provide unlimited constant-tension delivery. The dancer eventually reaches a stop unless payout and take-up balance. This board measures that problem; it does not implement the automatic brake release or feedback needed in a complete carrier.

Make the calibration board

1. Cut the 120 × 180 mm board from measured 6 mm stock. SVG and DXF dimensions are nominal; compensate for your measured kerf. Mount it upright using the top holes or clamps, leaving access to the back.
2. Print four rod clamps and the slider. Fit two deburred Ø4 × 147 mm rods at 56 mm centres. Align the clamps while the slider is on the rods, then secure them. Use the marked 80–120 mm height interval. The slider must move under its own weight before testing yarn; polish/ream the bores if necessary.
3. Print two pulleys and retainers. Check the bearing seat against the actual 623 bearing. Fit the bearing from the back and bond the retainer only at its outer annulus. Use the listed posts and inner-race shims; tighten the M3 axles onto the inner races without pinching a pulley or seal. Verify free rotation.
4. Fit the bobbin, stand-off, felt washer and measured compression spring on the M6 spindle. The spring is a reference envelope: its free length, stiffness and working preload must be chosen and recorded. Retain the spindle at the board and use the front nut to adjust felt preload. Wind a small test package; keep the yarn between the flanges.
5. Bond a measured ceramic eye into its holder, with its hole facing vertically along the thread. Assemble the illustrated route and attach a small mass to the lower slider hole. Weigh the entire moving assembly. Keep the hanging mass behind the yarn plane, clear of the loop and the board.
6. Pull the output slowly by hand using a suitable low-force gauge. Record upward and downward slider motion separately to expose friction. Do not motorise this calibration board. A clear hand traverse and nominal solid checks do not establish its dynamic performance.

Measure before choosing the carrier hardware

Measurement	What it tells us
Pull at several package radii, with dancer bypassed	Starting and running brake torque: τ ≈ pull × radius. Keep nut preload fixed and record both.
Pull while the dancer rises and descends, with supply anchored	Compare each direction with mg / 2. Their difference reveals friction and hysteresis.
40 mm used travel	80 mm stored length. The main tabletop paths currently need up to 20.29 / 28.65 / 36.27 mm of changing storage for 8 / 12 / 16 carriers. This board has geometric travel to test those ranges; it is not a fitted carrier.
Repeated hand payout	Record stick-slip, slack, stop contact, abrasion and package tangling. These observations decide whether to change the brake, slider or guide before integration.

The worksheet is deliberately blank. Repeat measurements and retain the instrument resolution. No material-force parameters have been invented to turn the geometric braid study into a physical prediction.

Evidence and boundaries

The slider and nominal assembly solids are checked at 41 heights. Axle, bearing and spring details use hardware envelopes; some fastening hardware and the hanging mass are specified rather than modelled. There is no physical build, wear test, print-fit qualification or complete yarn-contact validation. The moving pulley’s position is a control, not a force simulation.

Reference: the SKF bearing catalogue lists the 623 envelope as 3 × 10 × 4 mm. Match fits, washers and running clearance to the actual purchased bearing. Continue with the carrier guidance experiment or the full mechanism audit.