Ch 04Checkpoint
Checkpoint 04¶
Checkpoint · Chapter 04 — A/B drive units and front idlers
- 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.
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a_drive_frame_upperhas its two heat-set inserts;b_drive_frame_upperhas 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.
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_upperhas 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.