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Chapter 04 — A/B drive units and front idlers

One page per step

Read this chapter one step per page — big pictures, prev/next, and the same tick marks. This page is the whole chapter in one scroll.

Builds the four CoreXY sub-assemblies that carry the A and B belts — two motor-carrying drive units and two front idlers with their tension arms. Unlocks Ch 05 (gantry), which bolts all four onto the Y extrusions.

What you're building in this chapter: the four corners the two long belts run around. In CoreXY two motors fixed at the back pull two crossed belts, so nothing heavy rides with the toolhead (glossary). A is the rear-right corner, B the rear-left. Each drive unit is a two-half printed frame with flanged bearing stacks on two standing bolts and a stepper motor underneath. Each front idler is the same bearing sandwich without a motor, plus a blue tension arm. The two belts run at two heights, and most of this chapter sets those heights exactly. Everything is built on the bench and bagged.

Revali pointing
Two drive units, two idlers, all handed. Lay them out left and right. Chapter seven notices.

Time: 3.5–5.0 h hands-on, first build (survey §5.1 P04).

Sessions: 7 × ~30 min — the Pause: lines below break the chapter into 7 segments; every minute figure is a first-build estimate.

Prerequisites:

  • Ch 01 — Frame. Nothing from Ch 02 or Ch 03 is needed; this is bench work and can run in parallel with them (survey §5.1: P04 ← P01).
  • Print batch B03 — A/B drive units + front idlers, 1 plate, 8.5 h, 119 g black (print plan). front_idler_right_* go with the A drive, front_idler_left_* with B (Step 04.2).
  • Print batch B02 — the accent day, plate B02-P2, for [a]_tensioner_left and [a]_tensioner_right.
  • Print batch B00 — for pulley_jig.stl. Without it you are setting two different pulley heights with calipers.

Tools

  • Hex drivers 2 mm, 2.5 mm, 3 mm, 4 mm — a 2.5 mm ball-end helps at the M3×40
  • 1.5 mm hex — the pulley set screws (verify on bench against the kit's pulleys)
  • Temperature-controlled soldering iron + LDO brass M3 insert tip (4 heat-set inserts, Steps 04.3–04.4)
  • Printed pulley_jig.stl (Voron-2 STLs/Tools/)
  • Digital caliper — pulley height fallback, and to confirm both drives match
  • The free end of the kit's 6 mm A/B belt reel, uncut — the belt-path straightness check. Cutting belt waits for Ch 07's matched cut
  • Tweezers or a small screwdriver to place spacers into the stacks without dropping them
  • Masking tape + marker — label every assembly A or B as it is finished

Consumables: Loctite 243 (blue), for the pulley set screws if they are not already pre-applied.

Printed parts

Parts arrive in the bins named below (see the bin map in print/README.md#bins); check the bin label's list before you start.

Looks like STL Bin Qty Colour
a_drive_frame_upper.stl 04-A 1 Black
a_drive_frame_lower.stl 04-A 1 Black
b_drive_frame_upper.stl 04-B 1 Black
b_drive_frame_lower.stl 04-B 1 Black
front_idler_right_lower.stl 04-A 1 Black
front_idler_right_upper.stl 04-A 1 Black
front_idler_left_lower.stl 04-B 1 Black
front_idler_left_upper.stl 04-B 1 Black
[a]_tensioner_right.stl 04-A 1 Blue
[a]_tensioner_left.stl 04-B 1 Blue

All ten are in Voron-2 STLs/Gantry/AB_Drive_Units/ and STLs/Gantry/Front_Idlers/. Two more parts sit in those same folders and are not used here: [a]_cable_cover (Ch 07) and [a]_z_chain_retainer_bracket_x2 (Ch 06). Keep them bagged.

Hardware (chapter totals)

Fastener / part Qty Where
Stepper motor, 0.9°, LDO-42STH48-2004MAH(VRN) 2 one per drive (p.75, p.79)
GT2 pulley, 20 T, 5 mm bore, 6 mm wide (Pulley, 2GT, 20T, 5mm ID 6mm W) 2 one per motor shaft (p.75, p.79). The kit has exactly two; the four 9 mm 20T pulleys are the Z-drive pulleys used in Ch 02
F695 flanged bearing (5×13×4 mm) 16 6 per drive (p.74, p.78) + 2 per front idler (p.65, p.69). The A/B side uses F695 only — 625-2RS is the Z-drive bearing (Ch 02)
M5 precision spacer, brass — the manual's "M5 shim" 16 one above and one below every bearing pair
M5×30 BHCS 4 2 per drive, upper frame → lower frame (p.73, p.77)
M5×40 SHCS 2 1 per front idler — the idler axle: first the stack-building aid, then refitted from the top through the tension arm into its M5 nut and clamped firm (p.65–66, p.69–70)
M3×30 SHCS 6 3 per motor (p.76, p.80)
M3×40 SHCS 2 1 per front idler — the belt tensioner screw, through the frame's front wall into the arm's heat-set insert (p.67, p.71); set with the belt on in Ch 07 Step 07.5
M3 washer 2 under each M3×40 head (p.67, p.71)
Heat-set insert, brass, M3×5×4 4 2 in a_drive_frame_upper, 1 in each tension arm (p.64)
M5 hex nut 2 1 in each tension arm foot (p.64)

Read first

  • A and B parts are mirrored and swap silently. The A drive's printed frames carry a cutout the B frames do not have (p.73, circled). Only a_drive_frame_upper has the two heat-set insert bosses — b_drive_frame_upper has none. Build one complete assembly at a time; never have both sets of frames loose on the bench together.
  • Where each assembly ends up, standing in front of the printer: A = rear right, B = rear left. The official manual shows it (p.63, p.83 — A on the right, B on the left, seen from the front) but never writes it; the LDO wiring guide does, and the LDO Klipper config repeats it (## B Stepper - Left, ## A Stepper - Right). It follows that the A idler is the front right pair and the B idler the front left pair. src
  • The bearing stacks are the mistake everyone makes. Every F695 pair goes flange-out — the two plain faces touch, the two flanges face away from each other — with one spacer above the pair and one below. The drive's far post takes two such pairs (4 bearings, 4 spacers); the near post and each front idler take one (2 bearings, 2 spacers).
  • The A and B pulleys sit at different heights and face opposite ways: A is hub-down at 16.5 mm (p.75), B is hub-up at 6.5 mm (p.79). That difference is what stacks the two belt planes. No amount of belt tension in Ch 07 will fix it if you set them the same.
  • Short a bearing, spacer or pulley? This chapter needs exactly 16 F695, 16 spacers and the two 6 mm pulleys. Recount against your Ch 00 inventory sheet, then contact Fabreeko support. Never borrow a 9 mm Z pulley.
  • LDO's Build Notes have no entry for p.62–81. The only kit deviation in this whole chapter is the standing substitution from their p.19 note: brass M5 precision spacer everywhere the manual writes "M5 shim". src

Sources for this chapter:

Video coverage (Steve Builds, pre-release LDO kit — differs from Rev D+): Part 3 @0:58:20 (+3m), Part 3 @1:04:20 (+14m), Part 3 @1:07:20 (+10m), Part 3 @1:18:03 (+2m), Part 3 @1:23:20 (+9m), Part 5 @1:12:20 (+8m)

Step 04.1 — Lay the chapter out as four separate kits

What you're looking at: Manual p.62 opens the A/B section: ten printed parts, four sub-assemblies. Two drive units, each a two-half frame holding bearing stacks with a stepper bolted underneath, and two front idlers, the same without a motor. They are the four corners the CoreXY belts loop around.

Parts:

  • staged: the ten printed drive and idler parts
  • staged: F695 bearing ×16
  • staged: M5 precision spacer ×16
  • tool: four trays or bags

Do:

  1. Label four bench areas: A DRIVE, B DRIVE, A IDLER, B IDLER.
  2. Put a_drive_frame_upper + a_drive_frame_lower in the first, b_drive_frame_* in the second, front_idler_right_* + [a]_tensioner_right in the third, front_idler_left_* + [a]_tensioner_left in the fourth.
  3. Open one area at a time; mirrors never mix.

check Check

Ten printed parts placed, none left over. An eleventh is [a]_cable_cover or [a]_z_chain_retainer_bracket; bag those for Ch 07 and Ch 06.

Helper: Counts the bearings and spacers into four labelled trays, one per assembly.

Source: Voron manual p.62 · Voron-2 STLs/Gantry/AB_Drive_Units · Voron-2 STLs/Gantry/Front_Idlers

Step 04.2 — Fix which assembly is A and which is B

What you're looking at: Manual p.63 shows the four positions; the pair renders tell the printed parts apart. A is the rear-right drive and B the rear-left, so the A idler is front-right and the B idler front-left. On the idlers the give-away is height, not handedness.

Parts:

  • consumable: masking tape
  • tool: marker
  • tool: caliper

Do:

  1. Write the destination on every part: a_drive_* rear right; b_drive_* rear left; front_idler_right_* + [a]_tensioner_right front right; front_idler_left_* + [a]_tensioner_left front left.
  2. Positions are as seen standing in front of an upright printer.
  3. Caliper the lower idler frames: front_idler_right_lower 21.6 mm, front_idler_left_lower 11.6 mm.

check Check

Every part carries its destination in marker, and the taller of the two lower idler frames is the one labelled front right.

Helper: Writes each destination in marker as you call it out, then reads the caliper on both lower frames.

tip Tip

the upper frames are handed the other way: front_idler_right_upper is 12.0 mm, front_idler_left_upper 21.6 mm. Caliper those if the lower pair is ambiguous. The 10 mm lower-frame gap is the belt-plane split.

Caution

Rev D+ / LDO: the motor identity comes from the wiring guide, not the manual: A = rear right → HV-STEPPER-1, B = rear left → HV-STEPPER-0. Get this backwards and the machine moves diagonally on a straight-line jog. src

Source: Voron manual p.63 · LDO wiring guide (Rev D) · LDO Klipper config leviathan-printer-rev-d-sbv2.cfg · Video: Part 3 @1:18:02

Step 04.3 — Heat-set the two inserts in a_drive_frame_upper

What you're looking at: Manual p.64: the heat-set inserts for this chapter. Only four, two into a_drive_frame_upper and one into each tension arm. It is the only drive frame with insert bosses, so two blind 4.7 mm holes beside the motor bore are the A/B test.

Parts:

  • M3×5×4 brass heat-set insert ×2
  • a_drive_frame_upper ×1
  • tool: soldering iron with the M3 insert tip

Do:

  1. Find the two blind 4.7 mm bosses either side of the motor bore on a_drive_frame_upper, ~56 mm apart.
  2. At the temperature written on your iron, press each insert straight down until flush, part held flat. Let it cool.

Check

Both inserts flush and square. b_drive_frame_upper takes no inserts; bosses on it mean you picked up the A frame.

Tip

if you ran the B03 insert pass that Step 00.16 plans, just confirm the two are present and skip ahead.

Source: Voron manual p.64 · LDO heat-set insert tool guide

Step 04.4 — Heat-set one insert into each tension arm

What you're looking at: Manual p.64 and the two blue tension arms: levers carrying each front idler's bearing stack, drawn forward to tension a belt. Each is a C: top boss counterbored for the M5×40 head, foot with the M5 nut pocket, back wall with one stepped bore.

Parts:

  • M3×5×4 brass heat-set insert ×2
  • [a]_tensioner_left ×1
  • [a]_tensioner_right ×1
  • tool: soldering iron with the M3 insert tip

Do: Each tension arm has one through-bore stepping from 3.5 mm to 4.7 mm. Press the insert into the 4.7 mm end, the wider opening. The 3.5 mm section is the M3×40's clearance and must stay clear.

Check

Pushed in by hand from the plain 3.5 mm end, an M3×40 SHCS runs free and picks up thread only at the insert.

Source: Voron manual p.64 · LDO heat-set insert tool guide

Step 04.5 — Press an M5 nut into each tension arm foot

What you're looking at: Manual p.64: an M5 hex nut dropping into a pocket in the foot of each tension arm. The vertical M5×40 axle threads into that captive nut, so the bearing stack is clamped inside the arm and moves with it.

Parts:

  • M5 hex nut ×2
  • reused: both tension arms
  • tool: small flat screwdriver

Do: Drop an M5 nut into the hex pocket in the underside of each arm's foot. Seat it fully with a flat driver; it must sit below the face, never proud, or the arm will not lie flat.

check Check

The nut does not rock and does not stand above the foot. Nothing holds it in yet; keep the arms flat.

Source: Voron manual p.64

pause Good stopping point · ~30 min since the last one

the bench is split into four labelled kits, every part carries its destination in marker, the two inserts are in a_drive_frame_upper, one is in each tension arm and both M5 nuts are seated. Unplug the iron. Nothing is stacked yet.

Step 04.6 — A idler: stand the assembly-aid bolt in the lower frame

What you're looking at: Manual p.65: the A front-right idler starting. front_idler_right_lower is the taller of the two lower frames, 21.6 mm against 11.6 mm. The M5×40 standing in its boss is not a fastener yet but a temporary spindle for the bearing stack.

Parts:

  • front_idler_right_lower ×1
  • M5×40 SHCS ×1

Do: Lay front_idler_right_lower flat with its idler boss facing up. Push the M5×40 SHCS up through the boss from underneath so the thread stands vertically. It is only an alignment aid and comes out at Step 04.9.

check Check

The bolt stands square to the frame and the head sits fully home underneath. If it leans, the stack will not seat.

Source: Voron manual p.65

Step 04.7 — A idler: build the bearing stack

What you're looking at: Manual p.65: the bearing stack. F695 bearings are 5 × 13 × 4 mm with a flange on one face. Fitted plain face to plain face, their flanges point outward, forming a channel one belt wide. A brass precision spacer each end sets stack height.

Parts:

  • 2× M5 precision spacer
  • 2× F695 bearing

Do: Thread onto the standing bolt, bottom to top: M5 precision spacer, F695 flange down, F695 flange up, M5 precision spacer. The two bearings meet plain face to plain face, flanges pointing outward.

check Check

Sight the stack from the side: spacer, flange, plain, plain, flange, spacer. Both bearings spin freely and independently.

Caution

Rev D+ / LDO: the manual's "M5 Shim" is the brass M5 precision spacer in this kit — one per callout, never two stacked to make up height. src

Source: Voron manual p.65 · LDO Build Notes (Rev D) · Video: Part 3 @0:59:21

Step 04.8 — A idler: cap the stack with the upper frame

What you're looking at: Manual p.65: front_idler_right_upper, the 12.0 mm-tall cap. It captures the top spacer and closes the frame around the bearing pair; the two halves meeting with no gap proves nothing inside is out of place.

Parts:

  • front_idler_right_upper ×1

Do: Lower front_idler_right_upper over the stack so its nose captures the top spacer and the two frames meet along their mating faces.

check Check

The two frames sit tight with no gap and no rock. A gap means a spacer or bearing is out of place.

Source: Voron manual p.65 · Video: Part 3 @1:06:14

Step 04.9 — A idler: pull the aid bolt and slide in the tension arm

What you're looking at: Manual p.66 and the pair render: the blue [a]_tensioner_right sliding into the channel between the two idler frames. The two arms are mirrors of each other, the same C handed the other way. The wrong hand will not lie flat in the channel.

Parts:

  • reused: [a]_tensioner_right, insert and M5 nut fitted

Do: Pinch the two frames together, withdraw the M5×40 SHCS downwards, and slide [a]_tensioner_right into the channel until its top boss lines up with the upper frame's hole. Keep pinching; the stack is unsupported.

check Check

The arm sits flat in the channel and its top boss is concentric with the frame's top hole. If it fights you, it is [a]_tensioner_left.

Helper: Pinches the two idler frames together while you swap the bolt for the arm.

Source: Voron manual p.66

Step 04.10 — A idler: refit the M5×40 SHCS from the top

What you're looking at: Manual p.66: the M5×40 refitted from the top as the idler's axle. Its head seats in the arm's top boss and its thread runs into the M5 nut in the foot, clamping bolt, spacers, bearings and arm into one sliding unit. Not the tensioner.

Parts:

  • reused: the same M5×40 SHCS

Do: Drop the M5×40 SHCS in from the top through the arm's top boss and run it down into the M5 nut in the foot until the head seats and the stack is clamped firm. It threads into steel, not plastic.

check Check

Head seated in the arm's top boss, both bearings spin free, and the arm still slides fore-aft in the frame's slots (verify on bench).

Source: Voron manual p.66

Step 04.11 — A idler: fit the M3 washer and M3×40 SHCS

What you're looking at: Manual p.67: the M3×40 entering horizontally through the idler frame's front wall and threading into the insert in the arm's back wall. It is the belt tensioner: winding it in draws the arm toward the wall. It does not clamp the frame halves.

Parts:

  • 1× M3 washer
  • 1× M3×40 SHCS

Do:

  1. Washer under the M3×40 head; enter it horizontally through the frame's front wall, the face away from the extrusion, into the arm's insert.
  2. Run it in only until the arm meets the wall, snug. Step 07.5 sets tension.

check Check

Snug, not torqued (not specified — snug). The arm sits against the wall, washer captive, head flat on the frame's front face.

Source: Voron manual p.67 · Video: Part 3 @1:07:00

Step 04.12 — A idler: check your work

What you're looking at: Manual p.68: the finished A idler with five features circled. Together they say the axle, the tensioner, the bearing pair and the frame halves are all where they should be.

Parts: none.

Do:

  1. Compare the five circled features on p.68: axle head in the arm's boss; ribbed upper frame; bearing pair flanges out; M3×40 head and washer in the frame's side; foot-flange bolt hole.
  2. Set it in the A IDLER tray.

check Check

All five features match the page. Spin the bearing pair with a fingertip: it runs free with the frames closed.

Helper: Points to each circled feature on the page while you find it on the idler.

Source: Voron manual p.68

pause Good stopping point · ~40 min since the last one

the A (front right) idler is complete and checked against p.68: bearings flange-out, M5×40 axle in from the top and clamped firm into the arm's nut, M3×40 tensioner with its washer snug. An idler is a self-contained unit; never stop with the aid bolt withdrawn and the stack unsupported.

Step 04.13 — B idler: stand the assembly-aid bolt in the lower frame

What you're looking at: Manual p.69: the B front-left idler. front_idler_left_lower is the short one at 11.6 mm, so its bearing stack sits lower. That is why the B belt runs in a lower plane than the A belt.

Parts:

  • front_idler_left_lower ×1
  • M5×40 SHCS ×1

Do: Lay front_idler_left_lower flat with its idler boss up and push the M5×40 SHCS up through it from underneath. The B idler's boss is lower than the A idler's; that is correct.

check Check

Bolt vertical, head home. If the boss looks tall like the last one, you have the A idler's lower frame.

Source: Voron manual p.69

Step 04.14 — B idler: build the bearing stack

What you're looking at: Manual p.69: the same four-item stack as the A idler, spacer, F695 flange down, F695 flange up, spacer. Identical hardware, different frame height.

Parts:

  • 2× M5 precision spacer
  • 2× F695 bearing

Do: Bottom to top: M5 precision spacer, F695 flange down, F695 flange up, M5 precision spacer. Identical to the A idler.

check Check

No flange visible in the middle of the stack; both bearings spin free.

Caution

Rev D+ / LDO: brass M5 precision spacer in place of the manual's "M5 shim". src

Source: Voron manual p.69 · LDO Build Notes (Rev D) · Video: Part 3 @1:23:36

Step 04.15 — B idler: cap the stack with the upper frame

What you're looking at: Manual p.69: front_idler_left_upper, the tall one at 21.6 mm where the A idler's upper was short. The uppers are handed the opposite way to the lowers, so two that look alike means two of the same hand.

Parts:

  • front_idler_left_upper ×1

Do: Lower front_idler_left_upper over the stack until the two frames meet.

check Check

Frames flush, no gap, no rock.

Source: Voron manual p.69

Step 04.16 — B idler: pull the aid bolt and slide in the tension arm

What you're looking at: Manual p.70: [a]_tensioner_left going into the B idler's channel, the mirror of Step 04.9.

Parts:

  • reused: [a]_tensioner_left, insert and M5 nut fitted

Do: Pinch the frames together, withdraw the M5×40 SHCS downwards, and slide [a]_tensioner_left into the channel until its top boss lines up with the frame's top hole.

check Check

The arm lies flat in the channel; its boss is concentric with the hole above it.

Helper: Pinches the two idler frames together while you swap the bolt for the arm.

Source: Voron manual p.70

Step 04.17 — B idler: refit the M5×40 SHCS from the top

What you're looking at: Manual p.70: the M5×40 axle refitted from the top through the arm's top boss into its captive nut, mirror of Step 04.10. Clamped firm; it is the axle, not the tensioner.

Parts:

  • reused: the same M5×40 SHCS

Do: Drop it in from the top, through the arm's top boss, and run it down into the M5 nut in the arm's foot until the head seats and the stack is clamped firm, into steel.

check Check

Head seated in the top boss, both bearings spin free, and the arm still slides fore-aft in the frame's slots (verify on bench).

Source: Voron manual p.70

Step 04.18 — B idler: fit the M3 washer and M3×40 SHCS

What you're looking at: Manual p.71: the M3×40 tensioner and its washer through the B idler frame's front wall into the arm's insert, mirroring the A idler.

Parts:

  • 1× M3 washer
  • 1× M3×40 SHCS

Do: Washer under the head, in through the frame's front wall, the face away from the extrusion, into the arm's insert, until the arm is drawn up to the wall and the screw is snug. Step 07.5 sets it.

check Check

Snug, not torqued (not specified — snug). Head flat, washer captive.

Source: Voron manual p.71

Step 04.19 — B idler: check your work

What you're looking at: Manual p.72: the finished B idler with five circled features, plus the comparison that catches a hand error, the two idlers side by side. Their bearing pairs sit at visibly different heights, the separation between the two belt planes.

Parts: none.

Do:

  1. Match the five circled features on p.72: ribbed face, M5×40 head in the top boss, exposed bearing pair, M3×40 head with washer, foot-flange bolt hole.
  2. Set it in the B IDLER tray.

check Check

All five match, bearings free. Held side by side, the two idlers' bearing pairs sit at visibly different heights.

Helper: Points to each circled feature on the page while you find it on the idler.

Source: Voron manual p.72

pause Good stopping point · ~35 min since the last one

the B (front left) idler is complete and checked against p.72, and the two idlers sit side by side with visibly different bearing heights. Both are in their trays. Nothing is open.

Step 04.20 — A drive: upper frame face down, two M5×30 BHCS

What you're looking at: Manual p.73 and the pair render: a_drive_frame_upper, built upside down, flat insert face on the bench, so the two M5×30 stand up as the axles the bearing stacks thread onto. There is no pillar; the manual's post is the standing bolt.

Parts:

  • reused: a_drive_frame_upper, inserts fitted
  • M5×30 BHCS ×2

Do:

  1. Frame flat face up: drop the two M5×30 BHCS in from that face, into the 5.4 mm holes either side of the motor bore, 37 mm apart.
  2. Turn it over, holding the heads, so the threads stand up.

check Check

An A part: the cutout circled on p.73 and two heat-set inserts. Both bolts stand square, heads underneath and fully home in the plate.

Source: Voron manual p.73 · Video: Part 3 @1:04:59

Step 04.21 — A drive: two-bearing stack on the near post

What you're looking at: Manual p.74: the post nearer the motor bore, taking one bearing pair: spacer, two F695 flange-out, spacer. This post carries only one belt, so it takes half the stack of the other one.

Parts:

  • 2× M5 precision spacer
  • 2× F695 bearing

Do:

  1. Work on the near bolt, ~17 mm from the bore centre; the far one is ~34 mm. Measure if the drawing is unclear.
  2. Bottom to top: M5 precision spacer, F695 flange down, F695 flange up, M5 precision spacer.

check Check

One pair, flanges out, one spacer each end: four items, 10 mm of stack. Four bearings here means the wrong bolt.

Caution

Rev D+ / LDO: brass M5 precision spacer in place of the manual's "M5 shim". src

Source: Voron manual p.74 · LDO Build Notes (Rev D)

Step 04.22 — A drive: four-bearing stack on the far post

What you're looking at: Manual p.74: the post farther from the motor bore, taking two pairs. Both belt planes pass through this drive, so it needs two channels stacked, separated by the two spacers that meet in the middle. It is the most mis-stacked assembly in the build.

Parts:

  • 4× M5 precision spacer
  • 4× F695 bearing

Do:

  1. Work on the far bolt, ~34 mm from the bore centre. Measure if in doubt.
  2. Load two pairs bottom to top: spacer, F695 flange down, F695 flange up, spacer, spacer, F695 flange down, F695 flange up, spacer.

check Check

Eight items, 20 mm of stack, exactly two spacers touching in the middle, and no flange facing another flange.

Helper: Reads the eight-item stack order aloud and hands you each part in turn.

Caution

Rev D+ / LDO: all four "M5 shims" here are brass M5 precision spacers. src

Source: Voron manual p.74 · LDO Build Notes (Rev D)

Step 04.23 — A drive: close it with a_drive_frame_lower

What you're looking at: Manual p.74 and the pair render: a_drive_frame_lower, the other half of the printed frame, closing over both posts. The M5×30 bolts thread directly into the plastic of the lower frame, so they stop at closed-and-snug rather than torqued.

Parts:

  • a_drive_frame_lower ×1

Do:

  1. Lower a_drive_frame_lower onto both stacks, aligning the M5×30 threads with their blind holes.
  2. Run both bolts down alternately, two turns at a time, until the frames meet.
  3. Do not over-tighten: these bolts thread into plastic.

check Check

Both bearing pairs still spin free with the frames closed, and neither bolt was taken past closed-and-snug.

Source: Voron manual p.74

pause Good stopping point · ~25 min since the last one

the A drive frames are closed snug over both bearing stacks; the motor and pulley are not fitted yet. Put the closed frame in the A DRIVE tray; never stop with a stack loaded and the lower frame off.

Step 04.24 — A drive: set the pulley on the A motor at 16.5 mm

What you're looking at: Manual p.75: the A motor and its 20T 6 mm-wide GT2 pulley, set with the printed jig. The pulley height puts the belt in the same plane as the A idler's bearing channel; the underside of the jig's A tab repeats it without a caliper.

Parts:

  • stepper motor, 0.9° A/B ×1
  • GT2 20 T 6 mm pulley ×1
  • tool: printed pulley_jig.stl
  • tool: caliper

Do:

  1. Slide the pulley on hub first, teeth up.
  2. Stand the jig on the motor face beside the pulley, letters upright, A tab toward it.
  3. Drop it until its teeth underside is level with the A tab underside.

check Check

Caliper 16.5 mm, motor face to teeth underside, hub down. ~23 mm means pulley on tab, ~19.5 mm jig on feet.

Helper: Reads the caliper aloud while you slide the pulley along the shaft.

Jig misuse

the plate stands beside the pulley, never over the boss. Its two feet hang past the motor face; stood on the feet every height reads 3 mm high. Without the jig, set 16.5 mm with a caliper.

Caution

Rev D+ / LDO: the two A/B motors are 0.9° (LDO-42STH48-2004MAH(VRN)); the four Z motors are 1.8° and look identical. Read the label: -2004MAH = A/B (0.9°), -2004AC = Z (1.8°). Take an A/B motor, not a spare Z motor. This is why the LDO config carries full_steps_per_rotation: 400 in [stepper_x] and [stepper_y], set in Ch 12. src

Source: Voron manual p.75 · LDO Klipper config leviathan-printer-rev-d-sbv2.cfg · LDO 350 Rev D BOM · Video: Part 3 @1:11:48

Step 04.25 — A drive: threadlock and lock the pulley set screws

What you're looking at: Manual p.75: the pulley's two set screws. A set screw that backs out lets the pulley slip on the shaft, and a slipping A or B pulley shows up as prints that drift diagonally, not as an obvious failure.

Parts:

  • reused: the pulley's two set screws
  • consumable: Loctite 243
  • tool: 1.5 mm hex key

Do:

  1. Back both set screws out. Blue patch on the thread? Refit dry. Otherwise one drop of Loctite 243 each.
  2. Land the first on the shaft's flat, if any, then the second.
  3. Recheck the height.

check Check

The pulley will not twist or slide under firm hand pressure and still reads 16.5 mm.

Source: Voron manual p.75

Step 04.26 — A drive: offer the motor up with the cable exit inboard

What you're looking at: Manual p.75: the motor going into the frame, right way up now. The manual's rule is that the two motors' cables point at each other once both drives are on the machine, so both reach the same duct.

Parts:

  • reused: the A motor with its pulley

Do: Turn the drive assembly the right way up, motor below the frames, and offer the motor into the frame with the cable exit facing inboard, toward the middle of the rear extrusion where the B drive sits.

check Check

With A at the rear right, its motor cable exits toward the machine's centreline, not out toward the right skirt.

Source: Voron manual p.75 · Video: Part 3 @1:07:37

Step 04.27 — A drive: three M3×30 SHCS through the frames into the motor

What you're looking at: Manual p.76: three M3×30 running down through both printed frames into the motor's face. Three, not four: the fourth motor hole has no clearance hole above it.

Parts:

  • 3× M3×30 SHCS

Do:

  1. Line the motor's mounting holes up with the three clearance holes around the bore.
  2. Start all three M3×30 SHCS by hand down through both frames into the motor.
  3. Tighten evenly so the motor face pulls down square.

check Check

Three bolts, not four; the fourth motor hole is not used. All three pulled down evenly, motor face flat against the frame.

Source: Voron manual p.76 · Video: Part 3 @1:13:34

Step 04.28 — A drive: check your work and the belt path

What you're looking at: Manual p.76's elevation and the belt reel's free end used as a straightedge. The A pulley runs in the upper belt plane, level with the near pair and the far post's upper pair.

Parts:

  • tool: free end of the 6 mm belt reel, uncut
  • consumable: masking tape
  • tool: marker

Do:

  1. Motor down, compare against p.76's elevation: pulley in the upper plane, level with the near pair.
  2. Lay the belt end across the pulley teeth, near pair and far post's upper pair.
  3. Label it A: REAR RIGHT.

check Check

Belt path straight: belt flat on the pulley, the near pair and the far post's upper pair; no tilt, no flange contact.

Helper: Sights along the belt at eye level and says if it tilts.

tip Tip

the far post's lower pair sits 10 mm below the belt. That is correct: it carries the B belt, so leave the stack alone.

Source: Voron manual p.76 · Video: Part 5 @1:12:36

pause Good stopping point · ~25 min since the last one

the A drive is finished: 2-bearing near post, 4-bearing far post, frames closed snug, pulley at 16.5 mm hub-down and threadlocked, motor in with three M3×30 and the cable exit inboard, belt path checked straight. Labelled A — REAR RIGHT. This is the natural stop; do not leave a bearing stack loaded with the lower frame off.

Step 04.29 — B drive: upper frame face down, two M5×30 BHCS

What you're looking at: Manual p.77 and the same pair render: b_drive_frame_upper, laid out the same upside-down way. This is the B part, with no cutout lobe on the base plate and no insert bosses. Seeing either means you picked up the A frame.

Parts:

  • b_drive_frame_upper ×1
  • M5×30 BHCS ×2

Do: As at Step 04.20: flat face up, drop an M5×30 BHCS into each of the two 5.4 mm holes, then turn the frame over so the heads are underneath and the threads stand up.

check Check

This is a B part: no cutout and no heat-set inserts. Either one means you picked up the A frame.

Source: Voron manual p.77

Step 04.30 — B drive: four-bearing stack on the far post

What you're looking at: Manual p.78: the four-bearing post, drawn on the left on the B frame because it mirrors the A frame. It is still the post farther from the motor bore; the page position changed, the rule did not.

Parts:

  • 4× M5 precision spacer
  • 4× F695 bearing

Do:

  1. Work on the far bolt, ~34 mm from the bore centre. p.78 draws it left, p.74 right; measure.
  2. Load two pairs: spacer, F695 flange down, F695 flange up, spacer, spacer, F695 flange down, F695 flange up, spacer.

check Check

Eight items, two spacers meeting in the middle, no flange face-to-face anywhere. Same 20 mm stack as the A drive.

Helper: Reads the eight-item stack order aloud and hands you each part in turn.

Caution

Rev D+ / LDO: brass M5 precision spacers, not shims. src

Source: Voron manual p.78 · LDO Build Notes (Rev D)

Step 04.31 — B drive: two-bearing stack on the near post

What you're looking at: Manual p.78: the two-bearing post, nearer the motor bore, drawn on the right. With this the two drives hold six bearings and six spacers each.

Parts:

  • 2× M5 precision spacer
  • 2× F695 bearing

Do: On the near bolt, ~17 mm from the bore centre, drawn on the right on p.78: spacer, F695 flange down, F695 flange up, spacer.

check Check

Four items, 10 mm. Both drives now hold six bearings and six spacers each; count them before closing.

Caution

Rev D+ / LDO: brass M5 precision spacers, not shims — the last two of the sixteen this chapter uses. src

Source: Voron manual p.78 · LDO Build Notes (Rev D)

Step 04.32 — B drive: close it with b_drive_frame_lower

What you're looking at: Manual p.78: b_drive_frame_lower closing the B drive. Same plastic threads, same rule: closed and snug, then stop.

Parts:

  • b_drive_frame_lower ×1

Do: Lower b_drive_frame_lower onto both stacks and run the two M5×30 BHCS down alternately until the frames meet.

check Check

Do not over-tighten: these bolts thread straight into plastic. Both bearing pairs spin free with the frames closed.

Source: Voron manual p.78

Step 04.33 — B drive: set the pulley on the B motor at 6.5 mm — flipped

What you're looking at: Manual p.79: the B motor's pulley, fitted the other way up from the A drive's. The two pulley heights, 16.5 mm on A and 6.5 mm on B, separate the two belt planes; set them the same and the belts rub.

Parts:

  • stepper motor, 0.9° A/B ×1
  • GT2 20 T 6 mm pulley ×1
  • tool: printed pulley_jig.stl
  • tool: caliper

Do:

  1. Slide the pulley on teeth first, hub up.
  2. Stand the jig on the motor face beside the pulley, B tab toward it.
  3. Push it down to level its teeth underside with the B tab underside, 6.5 mm.

check Check

Caliper 6.5 mm, motor face to teeth underside, hub up. ~13 mm means pulley on tab. Side by side, A high, B low.

Helper: Reads the caliper aloud and says whether the pulley is the flipped one.

Source: Voron manual p.79 · Video: Part 3 @1:12:46

Step 04.34 — B drive: threadlock and lock the pulley set screws

What you're looking at: Manual p.79: the B pulley's set screws, threadlocked and re-measured, exactly as on the A drive.

Parts:

  • reused: the pulley's two set screws
  • consumable: Loctite 243
  • tool: 1.5 mm hex key

Do: Back both set screws out: refit dry if the thread carries a blue patch, else one drop of Loctite 243 each. First one onto the shaft flat if there is one, then the second. Re-measure with the jig and caliper.

check Check

No slip under hand pressure; still 6.5 mm.

Source: Voron manual p.79

Step 04.35 — B drive: offer the motor up with the cable exit inboard

What you're looking at: Manual p.79: the B motor going in with its cable exit inboard, mirrored from the A drive. Held in their finished positions the two drives' cables face each other across the back of the machine.

Parts:

  • reused: the B motor with its pulley

Do: Turn the assembly the right way up and fit the motor with the cable exit facing inboard, mirrored from the A drive, so with B at the rear left its cable also runs toward the machine's centreline.

check Check

Hold both drives in their build positions: the two cable exits face each other. That is the manual's own test.

Helper: Holds the A drive in its rear-right position while you hold B beside it.

Source: Voron manual p.79 · Video: Part 3 @1:16:29

Step 04.36 — B drive: three M3×30 SHCS through the frames into the motor

What you're looking at: Manual p.80: the same three M3×30 through both frames into the motor face.

Parts:

  • 3× M3×30 SHCS

Do: Start all three by hand through both frames into the motor, then tighten evenly.

check Check

Three bolts, motor face flat against the frame, nothing cross-threaded.

Source: Voron manual p.80

Step 04.37 — B drive: check your work and the belt path

What you're looking at: Manual p.80's elevation and the belt's free end again. The B pulley runs in the lower belt plane, level with the near pair and the far post's lower pair.

Parts:

  • tool: free end of the 6 mm belt reel, uncut
  • consumable: masking tape
  • tool: marker

Do: Motor down, compare against p.80's elevation: pulley in the lower plane. Lay the belt's free end across the pulley teeth, the near pair and the far post's lower pair. Label it B: REAR LEFT.

check Check

Belt path straight: belt flat on the pulley, the near pair and the far post's lower pair; no tilt, no flange contact.

Helper: Sights along the belt at eye level and says if it tilts.

tip Tip

the far post's upper pair sits 10 mm above the belt. That is correct: it carries the A belt, so leave the stack alone.

Source: Voron manual p.80

pause Good stopping point · ~45 min since the last one

the B drive is finished and labelled B — REAR LEFT, pulley at 6.5 mm hub-up, both cable exits facing each other when the drives are held in their build positions.

Step 04.38 — Bag, label and hand off to Ch 05

What you're looking at: Manual p.81 is a divider page with no assembly content. On the bench: four finished sub-assemblies, each of which only fits one corner of the machine, so each goes into a bag with its destination written on it.

Parts:

  • reused: the four finished assemblies
  • consumable: four bags
  • tool: marker

Do: Bag each assembly separately with its destination written on the bag: A drive: rear right, B drive: rear left, A idler: front right, B idler: front left.

check Check

Four bags, four labels, no loose bearings or spacers left on the bench. Leftovers mean a stack is short.

Helper: Writes A and B on the two bags and seals the leftover fasteners.

Source: Voron manual p.81

pause Good stopping point · ~15 min since the last one

all four assemblies bagged and labelled with their destinations, and nothing left over on the bench. Work through Checkpoint 04 before Ch 05.

Checkpoint 04

  • Two drive units and two front idlers built, each labelled with its position on the machine.
  • Every F695 pair is flange-out — plain faces touching — with one brass M5 precision spacer above and below each pair.
  • Drive far posts: 4 bearings + 4 spacers, with two spacers meeting mid-stack. Drive near posts and both idlers: 2 bearings + 2 spacers.
  • All six bearing groups spin free with the frames closed and bolted.
  • Both idlers: M5×40 axle clamped firm into the arm's nut, arm still sliding in the frame's slots; M3×40 tensioner snug into the arm's insert.
  • a_drive_frame_upper has its two heat-set inserts; b_drive_frame_upper has none.
  • Both motor pulleys are the 6 mm-wide 20T (5mm ID 6mm W), not one of the four 9 mm Z-drive pulleys.
  • A pulley: hub down, 16.5 mm. B pulley: hub up, 6.5 mm. The two are visibly different.
  • Both pulleys are threadlocked and will not slip under hand pressure.
  • The belt's free end lies flat on each pulley, its near pair and the far-post pair in the same plane: upper on A, lower on B. No tilt, no flange contact. The other far-post pair sits 10 mm off; it carries the other belt.
  • Both motor cable exits point inboard; held in their build positions, they face each other.
  • Every M5×30 BHCS is snug only — none was torqued down into the plastic thread.
  • Zero bearings, spacers or fasteners left over.
Revali passing a gate
You built four CoreXY corners: two drive units and two front idlers. 7 gummy worms.

Common mistakes

  • A bearing pair fitted flange-to-flange (or flange-in). The belt then rides on a flange edge instead of the bearing races and shreds. Fix: open the stack, turn the two bearings so their plain faces meet. Check by sighting the stack edge-on — a flange in the middle is always wrong.
  • Four bearings on the near post, two on the far post. The frames will not close square, or they close and pinch a bearing. Fix: the four-bearing stack always goes on the post farther from the motor bore — right on p.74, left on p.78.
  • Fitting a 9 mm 20T pulley on an A/B motor. It looks like the right pulley but it is a Z-drive part, and it will not sit in the 6 mm belt plane that a flange-out F695 pair forms. The kit ships exactly two 6 mm 20T pulleys and four 9 mm ones — count them before you start, and keep the 9 mm four with the Ch 02 Z bin.
  • Both pulleys set to the same height, or the B pulley fitted hub-down. The A and B belts then try to share one plane and rub. This is not fixable at belting time. Fix: A = 16.5 mm hub down, B = 6.5 mm hub up, both re-checked after the set screws are tight — the jig's tab underside level with the underside of the teeth, then the caliper.
  • Leaving the idler M5×40 loose because "it is the tensioner". It is the axle; the M3×40 through the frame's front wall is the tensioner (Ch 07 Step 07.5). Left loose, the stack rattles and the bearings tilt on the shank, found in Ch 07 as bad belt tracking. Fix: run it down firm into the arm's M5 nut.
  • Motor cable exits pointing outboard. The cables will not reach the drag chain and the drive has to come apart with the gantry in the machine. Fix: check before the three M3×30 go in — the exits face each other.
  • M5×30 BHCS torqued down. They thread into plastic (p.74, p.78) and strip permanently; a stripped post means reprinting a drive frame. Fix: stop at closed-and-snug.
  • A parts and B parts swapped. The A frames have a cutout and a_drive_frame_upper has two heat-set inserts; the B frames have neither. On the idlers, the tall lower frame is the A (right) idler.

Next

Ch 05 — Gantry: X and Y axes, XY joints, X carriage, titanium backers. The four assemblies you just built bolt onto the Y extrusions there (manual p.82–107); print batch B04 must be done before you start it.