Chapter 07 — A/B belts and tensioning

Time: 2.5–4.0 h hands-on, first build · Sessions: 5 × ~30 min · Steps: 39

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Before — end of Ch 06: gantry on the Z joints, Z belts run

After — end of Ch 07: A and B belts closed

What this chapter builds — orange is new, grey is what you already built. The A and B belt loops threaded through both idler stacks and closed at the X carriage, plus the inductive probe and the A/B drive cable cover. The CAD belt loops are the 250 lengths and the only thing on this picture that is size-dependent. Cut yours to Chapter 07 Step 07.8, never to this render.

StartBefore you start

Step 07.1Confirm the gate before you start

Step 07.2Learn the rule that governs this chapter

Step 07.3Trace the A belt path

Step 07.4Trace the B belt path

Step 07.5Set both front-idler tensionerswith a helper

Step 07.6Fit the heat-set inserts and M3 nuts

Step 07.7Set the two carriage stop screws to 3 mm

Step 07.8Cut both belts to the same length

Step 07.9Clamp the first end of both belts in the left carriage half

Step 07.10A belt: leave the carriage and turn at the left XY joint

Step 07.11A belt: run rearward up the left Y extrusion

Step 07.12A belt: turn 90° at the rear-left idler stack

Step 07.13A belt: S-wrap the A drive motor pulley

Step 07.14A belt: run forward down the right Y extrusion

Step 07.15A belt: U-turn at the front-right idler

Step 07.16A belt: turn at the right XY joint and return to the carriage

Step 07.17B belt: leave the carriage and turn teeth-on at the left XY joint

Step 07.18B belt: run forward and U-turn at the front-left idler

Step 07.19B belt: run rearward up the left outer run, past the left XY joint

Step 07.20B belt: S-wrap the B drive motor pulley

Step 07.21B belt: run right along the rear and turn 90° at the rear-right idler stack

Step 07.22B belt: run forward, turn smooth at the right XY joint and return to the carriage

Step 07.23Check both belts against the overviews before closing the carriagewith a helper

Step 07.24Fit the right X carriage half to capture the belt ends

Step 07.25Fix the belts, lightly

Step 07.26Fit the carriage bolts and leave them loose

Step 07.27Pull both belts tight and equalise the tailswith a helper

Step 07.28Tighten the carriage bolts

Step 07.29Belt-rub inspection at every idler stackwith a helper

Step 07.30Set the 150 mm measuring spanwith a helper

Step 07.31Read both belts with the phonewith a helper

Step 07.32Bring both belts to ~110 Hzwith a helper

Step 07.33Move the gantry, return, and re-check

Step 07.34Insulate the probe and keep its lead whole

Step 07.35Fit the probe and its retainer bracket

Step 07.36Set the probe heightwith a helper

Step 07.37Route the probe cablewith a helper

Step 07.38Hall-effect endstop magnet: skip

Step 07.39Fit the A/B drive cable cover

Checkpoint 07Tick before moving on

Gather per session — what to lay out before each bench segment.

• Steps 07.1–07.5 · ~25 min — Already on the bench: the two front-idler M3×40 SHCS; the two front-idler M3 washers
• Steps 07.6–07.8 · ~30 min — Fasteners, Tools & Misc box: M3 heat-set insert ×4; M3 nut ×2; M3×12 SHCS ×2 · Printed parts: x_frame_V2TR_MGN12_left ×1 (bin 07-X); x_frame_V2TR_MGN12_right ×1 (bin 07-X); probe_retainer_bracket ×1 (bin 07-X) · Tools and consumables: Gates 2GT open belt, 6 mm wide, two equal lengths
• Steps 07.9–07.28 · ~80 min — Fasteners, Tools & Misc box: M3×8 SHCS ×4; M3×30 SHCS ×2 · Already on the bench: the left X carriage half; both cut belts, marked A and B; the A belt; the B belt; the right X carriage half; both belts, tails loose
• Steps 07.29–07.33 · ~30 min — nothing to lay out
• Steps 07.34–07.39 — Cable Kit 2.4-350 box: Omron TL-Q5MC inductive probe ×1 · Fasteners, Tools & Misc box: M3×30 SHCS ×2 · Printed parts: [a]_cable_cover ×1 (bin 07-X) · Tools and consumables: fibreglass tape 2×12 cm · Already on the bench: the probe retainer bracket

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