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Three phases, one bed heating per phase

The situation

Forty-eight printers on a three-phase supply, roughly sixteen per phase. A bed heater is the single biggest load a printer draws, and it draws it at the start of the print. When a shift ends the operator walks the shop and clears plates; the queue starts a dozen prints inside one scheduler tick, twelve beds climb at once, and the breaker on one of the phases goes.

A farm-wide cap of two starts stops the breaker and wastes two phases: "two beds anywhere" is one phase's worth of load, and the other two phases sit idle while the queue waits.

The goal

On every phase, at most one bed climbing at a time — or two, whatever that circuit tolerates — and the three phases independent of each other. A plate-change round then runs three starts at once, one per phase, and the queue never needs to know which socket a printer is plugged into.

What is involved

Feature Its part
Printer tags Name the phase on each printer. A tag is a label with a colour; here it means "this printer is on phase 2".
Staggered start → Groups Turns the one farm-wide cap into a cap per tag — and, if you want, per room as well.
The stagger banner On the Queue page: occupancy per phase, and which printer a waiting item is waiting on.

Step by step

  1. Name the phases. Settings → Printing → Tags: create Phase 1, Phase 2, Phase 3. Give each a colour from the palette — the banner and the printer cards will wear it, which is how you tell at a glance which phase is full.

  2. Tag every printer. Edit each printer and pick its phase tag in the field under the location. On the Printers page, group the cards by Tag: the section No tag at the bottom is your to-do list, and it has to be empty before the next step (see the first pitfall for why).

  3. Turn the split on. Settings → Printing → Queue & Scheduling → Staggered Start:

    Setting Value for this farm
    Enable staggered start On
    Concurrent starts 1 — the field relabels itself to Concurrent starts per group the moment a split is on, and that is what it now means
    Interval (minutes) 3 — the recovery gap after a bed has reached temperature, not the heat-up time
    Wait for bed to heat On
    Split by printer tags On, and tick Phase 1, Phase 2, Phase 3

  4. A weaker phase, optionally. Beside each ticked tag there is a small number field. Leave it empty and the phase uses the number above; put 1 on the phase with the smaller breaker and 2 elsewhere and each phase runs on its own limit.

  5. Two workshops, optionally. If two rooms have separate feeds, turn Split by location on as well and tick the two rooms. The groups become phase × room — Phase 1 · Workshop 2 — and each pair has its own cap, the smallest of its tag limit, its location limit and the global number.

  6. Look at the Queue page. The banner above the queues now has one segment per phase — Phase 1: 1/1, Phase 2: 0/1, Phase 3: 1/1 — and next free in with a countdown. Clear plates exactly as before.

What BamDude does on its own after that

  • Every print start takes a slot in the printer's phase — a queued job, Print, a re-print from the archive, and a print you start on the printer's own screen with a cold bed. Once a phase's slot is taken, the next item on that phase waits with the reason on its row:

    Staggered start [Phase 2]: waiting for P1S-04 to heat up

    Items on the other two phases do not wait for it.

  • The slot is held until the bed is at target (within ±1 °C), then for the interval on top, and only then does the next start on that phase go. A printer that is already at temperature when its print starts is skipped — its spike is behind it.

  • A direct print waits like a queued one. Press Print on a phase that is full and the dialog waits for a slot, then uploads. With Strict mode for direct dispatch on it is refused instead — Stagger cap reached — and nothing is uploaded.

  • A restart forgets the slots and finds them again. A few seconds after MQTT is back, every printer found heating a bed gets its slot re-registered, so a restart mid-heat does not hand out a free pass.

  • A tag pinned mid-heat counts from the next tick. Groups are re-read on every scheduler pass; nothing has to be restarted after re-tagging a printer.

Pitfalls and what-ifs

An untagged printer counts on every phase

A printer with none of the picked tags is a wildcard: BamDude does not know which phase it is on, so it is treated as if it could be on any of them. It starts only when every phase has room, and while it heats it occupies a slot on every phase at once.

Turn the split on with a half-tagged farm and starts get rarer, not smarter. Tag everything first — the No tag group on the Printers page is the check.

  • The interval is the recovery gap, not the heat-up time. With Wait for bed to heat on, the climb is already covered by the bed wait. Two to five minutes is plenty; ten just slows the farm.
  • One slow heater on the phase. Set Stagger interval (minutes) on that printer's edit form (0 = the farm default) rather than raising the whole farm's interval.
  • A phase tag cannot be deleted while it is a group. The API answers 409 — un-tick it under Queue & Scheduling first, then delete. Silently redrawing which printers share a cap is not something a delete button should do.
  • The forecast does not see stagger. Ready ≈ on an order is computed without it and says so in its list of assumptions. A farm that staggers hard will finish a little later than the date — see The customer asks when fifty will be ready.
  • Nothing here slows the dispatcher. Uploads to several printers still run in parallel; the cap gates the start of the print and nothing else, so a print already running is never slowed by a neighbour waiting for a slot.
  • A tag means whatever you say it means. The same mechanism splits by room through locations; splitting by tag is for anything a room does not describe — a phase, a UPS, an extension lead.