How to track filament inventory

Every shop has had the night. The roll looked full enough when it went on, the print was long, and somewhere in the small hours the printer stopped with half a part on the plate. The plastic is gone, the machine time is gone, and the job starts again.

Filament tracking answers two questions: will this roll finish this print, and what is on the shelf before I promise the next order. Here are the ways shops answer them, what each one is good for, and where each one stops.

By eye

Looking at the roll costs nothing and takes no time. On a short print with plenty left it is enough. It fails on the long print with a roll that is getting thin, which is the one print where being wrong costs the most.

The scale and the tare

A kitchen scale answers the question properly: weigh the roll and subtract what the empty spool weighs. The catch is the empty spool. Bambu Lab lists its reusable spool at 250 g. Bambu Lab store Spools vary even within one maker: a user on Bambu’s forum weighed three kinds of Bambu spool at 245 g, 255 g and 253 g, cardboard core included. Bambu Lab forum

A guessed tare is how a scale goes wrong. The same thread opens with “I just wasted 200g of the very expensive PpA-CF because of a miscalulation of weights.” Bambu Lab forum

The fix is to weigh each new roll when you open it, before it loses a gram, and write the full weight on the spool. Another user in that thread does exactly that, subtracting the nominal filament weight to get the spool’s own weight and writing it on painter’s tape on the side. Bambu Lab forum From then on the scale reading minus that number is what is left.

The scale answers for the roll in your hand, today. It remembers nothing, so the next roll and the next print start from zero again.

The AMS estimate

Bambu’s AMS shows a remaining amount for the roll in each slot. It is an estimate from how much filament has been fed, not a weight. As one forum regular puts it: “The AMS detection is good to an eighth of a spool at best, and is also for Bambu spools only.” Bambu Lab forum

That is useful for the roll on the machine. It says nothing about the rolls on the shelf, and nothing about a third-party roll in the same slot.

Bambu’s Filament Manager

Bambu Studio’s Filament Manager keeps a list of your spools with a remaining weight. Its own wiki page states the limits plainly: Bambu Lab wiki

• “Read from AMS only works with Bambu Lab spools that carry an RFID tag. Third-party spools do not contain RFID data and must always be added using Manual Add.” Bambu Lab wiki
• “Weight updates after a completed print - not in real time during a print.” Bambu Lab wiki
• “There is no automatic low-filament warning.” Bambu Lab wiki
• “Sync requires an active internet connection.” Bambu Lab wiki

For a shop that runs only Bambu filament on Bambu machines, it is a reasonable record. A shelf with other brands on it needs those rolls typed in by hand, and the record lives with the slicer, not with your orders.

Spoolman

Spoolman is free, open-source software you host yourself. Its README describes it as a “self-hosted web service” that, when connected to OctoPrint or Klipper, “automatically updates spool weights as printing progresses”. Spoolman

On a Klipper or OctoPrint machine that is the best deduction there is, because nobody has to log anything. The trade is the server: something in the house has to run it, and a printer that does not report to it gets none of the automation. The Printyard and Spoolman comparison covers where each fits.

A spreadsheet

A sheet with a row per roll and a column for what is left works for a handful of rolls. It needs every print typed in, on a laptop that is usually not next to the printer, so it drifts from the shelf as soon as a busy week skips an entry. The spreadsheet comparison shows the sheet worth building if you stay with one.

An app at the machine

The step that keeps any record honest is logging the print where it happens. Printyard keeps every roll as a record with what is left on it, takes a logged print off the roll it ran on, purge included, and turns a roll red when it drops under its reorder point. A tag or a QR label on the spool opens its record.

It is not automatic. Printyard does not talk to the printer, so the roll comes down when you log the print. Printyard cannot read Bambu’s own spool tags, so a Bambu roll gets a tag or label of your own. The comparison of phone apps sets it beside the others.

Track the money, not only the grams

Grams on the shelf are money on the shelf. A roll is worth its price divided by its net weight, per gram, and the purge a multi-colour print throws away costs the same per gram as the part. The filament cost calculator turns a spool price into a cost per gram and prices a print with its purge. The material pages do the same for PLA, PETG and the rest.

A routine that holds

• Weigh each new roll when you open it, and write the full weight on the spool.
• Log each print against the roll it ran on, failed prints included, because that plastic is gone too.
• Weigh a roll before a long print, and trust the scale over the estimate.
• Set a reorder point per material, and reorder when a roll crosses it, not when it runs out.