Ch 02Checkpoint

Checkpoint 02

Checkpoint · Chapter 02 — Z drives, Z idlers, Z rails, deck panel

What you should have now — The four Z drive units under the frame, the four idler cages above them, the Z rails and carriages on the verticals, and the deck panel. CAD rails are MGN9 300 mm; your 350 kit uses 400 mm rails, and the deck panel is the 350 one.

• All four Z rails run their full travel with no notch, tight spot or grinding; every carriage is taped or stoppered.
• Rail surfaces are clean and dry and grease is inside the carriages only — carried over from Ch 00 Steps 00.18–00.21 and re-confirmed at Step 02.05.
• All four rails are centred on their extrusions, each facing the rail on its own side of the machine (front-left ↔ rear-left, front-right ↔ rear-right), and share the same 3 mm bottom gap and the same nine-hole pattern (holes 2–18, no end holes).
• Deck panel notch is at the back; panel sits inside the frame opening under the bed extrusions, held up by eight clip ledges, no rock; four M5 T-nuts aligned under the four deck holes and left unbolted for Ch 09 Step 09.5.
• _a parts at Z0 and Z2, _b at Z1 and Z3 (or the reverse if the Step 02.29 dry-fit said so — written in the build log), and each idler the same hand as the drive below it.
• Measured deck-panel thickness is written down and the fitted deck supports (8 off) match it.
• Every 20T drive pulley sits 33 mm along its shaft; every 16T motor pulley sits 10.7 mm off the motor face.
• All 24 M4×4 set screws are tight, threadlocked, and at least one per pulley lands on the shaft flat.
• Four M5 precision spacers per drive (16 total) — spacers, not shims.
• Each Z drive shaft turns freely by hand through the belt, with no belt skip and no bearing rumble.
• All four tensioner cams are closed and no drive shifted when its cam closed (p.46 check).
• Four rubber feet fitted; the printer stands on all four without rocking on the reference surface.
• Each Z idler faces the same way as the pulley in the drive below it and is pressed hard into its corner.
• Four motor cables labelled Z0 / Z1 / Z2 / Z3 by physical corner.

You built four Z drives, four idlers, four rails and a clipped-in deck. 11 gummy worms.

Common mistakes

• Bolting a rail on dry. Once a rail is on an extrusion you cannot use the flip-and-pack method, and a dry MGN9 wears out. Rails off again, or a compromised axis — check at Step 02.05 that Ch 00 really did all four (§5.2 W9).
• Missing a heat-set insert before the drive is closed. Six M3×40 have to come out and the shaft assembly has to be lifted to reach it. Do the insert pass as a batch, count the pockets, and only then start assembling (§5.2 W3).
• A 20T pulley on a Z motor. The 16T and 20T look nearly identical. The machine will home and move and be silently wrong on every Z dimension, because gear_ratio: 80:16 is baked into the config. Count teeth, then clear the 16T pulleys off the bench (p.38).
• Skipping the deck supports "until the panels chapter". The deck cannot be lifted once the gantry and electronics are in — the frame has to come partly apart. LDO puts this at p.29–30 for a reason (§5.2 W4).
• Tightening rail screws from one end. The rail bows and the carriage develops a tight spot that no amount of greasing fixes. Always centre-outward (p.24).
• Set screws finger-tight or off the flat. They loosen under Z load, the belt slips, and the gantry drops out of level. Threadlocker on all of them, one on the flat, tightened with a proper hex driver (p.32, §5.2 W12).
• Closing a drive with the halves upside down. Screws started from above into the retainer's visible brass inserts thread only into that insert, clamp nothing, and pull the insert out of its boss. The M3×40 heads sink into the main's counterbores; the retainer's inserts are at the bottom of the stack (Step 02.24).
• The wrong hand at a corner. It bolts on fine and shows up in Ch 06 when the 20T is not under its idler. Diagonals share a hand (Step 02.02); dry-fit the first unit (Step 02.29).
• M5×40 through the motor foot. The foot's holes are 9 mm deep M5×10 holes; a 40 mm screw bottoms in the slot and jacks the T-nut. The long screws go down the drive body's wells (Step 02.31); the motor foot takes the two M5×10, both left loose until the cam is closed (Steps 02.32–02.33).
• Cam at the wrong end of the foot. The tensioner lives under the drive end of the motor foot, on the drive-end screw; at the motor end it has nothing to push against and the loop never comes taut (p.43, Step 02.33).
• Bolting the deck down here. The four M5×10 go in with the DIN rails in Ch 09 Step 09.5. Fitting them now means undoing them again — and it double-counts the same four bolts in two chapters' hardware totals.

Next

Chapter 03 — Build plate: bed, magnet sheet, spacers and the M3×20 mounting screws (manual p.52–61, with LDO's p.55/56 skips).

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Next →Ch 03 — before you start