How come prints finish much earlier than BS estimated?

[Tbenker]

Not that i complain but i used to observe just the opposite in the past.

After doing some mid size warm up prints with my new P1S, i built confidence that i can try longer prints like 19 hrs+. As i was printing short or mid size prints i did not pay attention before but after completed three 19+ hrs prints i realized that the prints finished about an hour earlier than slicer estimated and what device tab showed at the very beginning of the print.

As the room is rather cold, 15C, and lots of drags i need to keep the door closed. There is only a tiny slit on the top cover which i achieved by placing 1.5 mm wedges on the front. I am using Creality Hyper PLA, manually tested calibrated all parameters. Maximum volumetric flow showed 26.5 would be possible but i set it to 22 to be on the safe side. I may increase gradually depending on my results.

All these prints were single color. So no time spent for filament changes. In the last print it had to use autofill once. That’s all.

The only thing i can think of is, BS assumes i will keep the door open as BL suggests and allocate more time for nozzle heating. As the chamber is much warmer the nozzle do not cool a lot that needs less time to reheat.

I am just curious.

[Olias]

This topic has been discussed previously both here and on some Cura and Prusa forums. While I don’t recall seeing a definitive explanation, the consensus seemed to be that the filament usage calculated by the algorithm can vary significantly based on conditions(filament moisture and density) and filament tolerance. I intentionally avoided using the term “quality,” as my understanding is that filament quality and tolerance are not directly related.

For discussion purposes, let’s assume time calculations are based on filament usage, which is determined by length. A quick search provides the following variations represented as percentages and their equivalent in meters:

• Percentage variation for ±0.02mm tolerance: ±1.14%
• Percentage variation for ±0.05mm tolerance: ±2.86%
• For a 1,000-meter spool:
  – Maximum decrease in length: -54.78 meters
  – Maximum increase in length: +23.26 meters

So you can see that this variation alone across a larger print would create greater deviations. In fact, I’ve seen great deviations with prints that were under 3 hours.

Also, I have noticed that the number of nozzle movements has a severe impact. For example, if I print a large cube primitive, the calculation is much more accurate regarding total time-to-print compared to something like a complex model with lots of micro-movements with similar time-to-print estimates.

I’m assuming there are some thoughts on this, but either the problem is very hard to solve, or nobody has found it significant enough to dive into.

There’s one area I’ve always wanted to experiment with, but it would probably happen only during an OCD episode. The filament settings include a value for filament density. Some have suggested this can be calibrated by printing a model of a specific weight and dimensions, then recalculating the density for each filament. Talk about having too much time on one’s hands.

For those interested, the setting can be found here:

I suppose, if someone were so inclined, they could print a cube primitive with 100% wall loops and zero top and bottom layers for consistency. Then scale the cube to 10x10x10mm, weigh it, and calculate the grams per square millimeter. For greater accuracy, increase the dimensions—though that could get expensive and time-consuming. But hey, if you can afford one of these printers, what’s a few wasted spools among friends?

[Tbenker]

@Olias

The filament settings include a value for filament density.

Thx for reply.

Creality lists the density for hyper PLA as 1.25 g/cm3. It is 1.24 g/cm3 in BS filament profile. There will be no argument between friends for 1%. or worth calibrating.

Roughly 1140 min /1080min => apprx 5.5%. ???

When the print time is longer I can accuse bottlenecks ie SD card, slow control card, friction, poor filament, damaged/ semi clogged nozzle etc. This is the first time i have seen it shorter. Anyways, as I said i can not complain. Just curious.

[Alex_vG]

I don’t think that the filament itself has anything to do with the print duration.
If density is off, the part will be lighter or heavier than expected, but I don’t see how it would affect the print time.
Same for flow rate or filament diameter. If one of those is off, it would cause over or under extrusion but no difference in time.

I think it has to be something where the slicer makes a guess of what the printer will do and that is off. Maybe the printer makes retractions with a single gcode command and assumes a certain time but the printer is 100ms faster. If you have 5000 retractions in a print, that would sum up to 500 seconds.