The real cost of a failed print

When a print fails, the thing everyone looks at is the tangle of plastic. It is the visible loss, so it becomes the measured one.

It is also not where most of the money went.

One failure on a day-long print

A large functional part: 680 g, 26 hours, on a 400 mm-class machine drawing about 230 W, filament at $32 a kilogram, machine amortised at 45 cents an hour.

The plastic is the biggest single line, but it is not the majority. A third of what a failed attempt consumes is machine time — wear on the nozzle, the belts, the plate and the fans that happened whether or not you got a part at the end. The electricity, which is what people always ask about, is barely a dollar.

The wattage in that table, incidentally, is an estimate inferred from the machine's class rather than a plug-meter figure for the model itself, and the calculator prints that caveat alongside the answer. It matters less here than elsewhere, because electricity is the smallest line on the list — but a figure whose provenance is hidden is a figure nobody will ever go back and check.

The same failure rate, a quarter of the cost

Now the part that is actually actionable.

Suppose twelve prints in a hundred fail. Applied to the print above, and assuming a failed attempt runs to completion before you discover it, the allowance is $4.75 per delivered part — a multiplier of 1.1364, which is bigger than the failure rate for reasons the failed-print method page derives properly.

Change nothing about how often prints fail. Change only when you find out. If failures are typically caught about a quarter of the way in, the same twelve percent costs $1.19 per part instead. The whole job goes from $39.55 to $35.99.

Four times less, from an identical process failing at an identical rate. The only difference is elapsed time before the abort.

Worth being explicit about the assumption underneath both figures. The default treats a failed attempt as consuming everything a successful one would, because that is what the failures that actually cost money look like: a warp discovered on removal, a detachment found in the morning, a part that finished and was wrong. Assuming failures are caught early is the optimistic case, and it should be an assumption you have earned by watching, not one you have adopted because it produces a nicer number.

This is the lever almost nobody optimises, because the failure rate is the number that feels like the problem. Reducing a failure rate is slow work: profile tuning, drying, plate cleaning, mechanical maintenance. Reducing the time-to-detection is mostly a matter of looking, and it is available immediately.

The slot you cannot buy back

There is a cost above that does not appear in any of these tables.

A 26-hour print that fails at hour 25 has consumed a day of machine availability. If you have a queue — a customer, a deadline, a batch that has to ship — that day is the expensive part, and no amount of cheap filament compensates for it. It is also why the failure cost of a long print is not just proportionally larger than that of a short one: the material scales linearly, the schedule damage does not.

Anyone running more than one machine has already learned this, usually the hard way. It is the reason print farms obsess over first-layer reliability rather than over material prices.

You are almost certainly measuring your failure rate wrong

Three systematic undercounts, all of them common.

The aborts you do not count. A print stopped at three minutes because the first layer looked wrong is a failure. People do not count it, because they caught it and nothing was wasted, which is precisely backwards — it is a free sample of exactly the information you need about your process.

The reprints you chose. A part that came out functional and that you printed again because a seam annoyed you is a failure of your standard, not of the machine, and it costs the same money either way.

Selection bias in what you remember. Nobody has ever finished a spool and thought "that was nine failures". They remember the two spectacular ones. If your honest answer to "what is your failure rate" is a shrug, assume it is higher than you would say, and go and count for a month. What a failed print costs is a much less interesting question than what yours costs.

What actually reduces the bill, in order

• Watch the first layer. Most failures are decided in the first two millimetres, and nearly all of them are visible there. This is the single highest-return habit on the list, and getting a repeatable first layer is the thing that makes it unnecessary.
• Set up remote monitoring. Anything that shortens time-to-detection converts an expensive failure into a cheap one. A camera earns its price back on one saved overnight job.
• Fix the failures that repeat. If prints fail at the same height, that is a mechanical or thermal cause with a fixable root, not bad luck.
• Dry the material that needs it. Popping, weak layers and mid-print jams have a cheap cause; drying is the cheapest intervention on this entire page.
• Check the spool before a long job. A tangle at hour eighteen is a total loss with a thirty-second preventive check.
• Print big jobs in pieces. Four six-hour prints and one twenty-four-hour print use the same plastic, but the four fail one at a time.

Abandoning a print on purpose

A print that is visibly going wrong is a sunk cost, and the arithmetic on sunk costs is unforgiving: everything already spent is gone whichever choice you make, and the only live question is what the remaining hours are worth.

If a part has detached, warped past tolerance or turned into spaghetti, the remaining hours buy nothing at all — stopping is free money. The harder case is the part that will probably be acceptable. There the honest question is whether you would accept it if it arrived from someone else, and if the answer is no, every further hour is being spent to avoid admitting the first ones were.

None of this shows up as a number in the slicer, which is the general problem with failure costs: they are the largest input nobody displays. Costing a print properly from the start puts them next to the ones that are displayed, and machine wear per hour is the other half of what a scrapped attempt really consumed.