Begin by defining the clock
A slicer estimate, the printer's elapsed timer and a promised handover time can describe different intervals. Decide whether you are comparing extrusion only, machine occupation from start to completion, or the whole workflow including cooling and removal. A five-hour toolpath estimate plus fifteen minutes of heating is not necessarily a fifteen-minute motion error. Record the same start and finish events for each comparison. This simple definition prevents useful timing data from being mixed with unrelated preparation or post-processing stages.
Compare estimate with elapsed time
View data table
| Comparison | h |
|---|---|
| Slicer estimate | 4 |
| Elapsed time | 4.6 |
The exported job and machine settings must agree
A slicer plans using a printer profile, speeds, acceleration assumptions and other limits. The machine may use another configuration or an active override. A faster-looking nominal speed does not prove the firmware reaches it. Compare the exact exported file with the actual printer profile and avoid changing settings during the measurement. If you modify firmware acceleration or feedrate limits, repeat the comparison rather than carrying an old error percentage into the new configuration. Keep the file revision with the observed time so a later reslice does not replace the evidence.
Short paths behave differently from long paths
On a long straight move, acceleration can bring the toolhead close to the requested speed. Small features and repeated corners spend more time accelerating or decelerating. For an ideal rest-to-rest move, reaching speed v and returning to rest takes a minimum total distance v²/a. At 100 mm/s and 1000 mm/s² that is 10 mm. Real corner velocities and planning are more complex, but the example explains why a tiny detailed part may gain little from raising a nominal speed. Toolpath geometry matters as much as the largest speed number.
Flow and cooling introduce additional limits
A high material throughput demand may cause the slicer to reduce extrusion speed to its volumetric cap. Small layers can also slow down to satisfy cooling time. Wide lines, thick layers, bridges and feature-specific settings need separate consideration. Travel, retraction and tool changes add time without following the same deposition formula. Check the speed and flow previews for the actual job instead of estimating duration from a bounding box or a model's solid volume. Those geometric quantities cannot specify the machine's timing behaviour.
Separate ordinary bias from interruptions
Suppose comparable jobs repeatedly take 330 minutes when the slicer estimates 300. The observed ratio is 1.10, suggesting a ten-percent scheduling allowance under those conditions. One job delayed two hours by a manual filament change does not establish a 40% motion bias for every future part. Record pauses, failed starts, user interventions and profile changes separately. A planning buffer handles ordinary uncertainty, while occasional interruptions need contingency. Avoid fitting one percentage to a mixed list of unrelated causes and then claiming it is a calibrated prediction.
Use declared G-code metadata as evidence
A supported time comment can show the estimate carried by the exported file. The G-code analyzer reads explicit metadata but does not simulate motion. Comments may be stale or describe another profile. If the comment and current slicer display disagree, verify whether the file was actually regenerated. Do not manufacture a new precise time by summing motion distance over feedrate; that ignores acceleration, waits and firmware rules. When no reliable declaration exists, obtain a fresh estimate from the intended slicer workflow.
Build a small timing log
For each representative job, save estimated duration, actual machine interval, profile revision and noteworthy interruptions. Group comparable work, such as long infill-heavy parts versus small detailed objects, rather than forcing everything into one average. Inspect both the absolute difference in minutes and the relative difference. A fixed heating delay matters proportionally more for a short print. Use the finish-time tool to schedule from a justified estimate and buffer, and check live printer state before promising completion. The aim is a reproducible planning model with visible limits.
Timing comparison log
| Record | Purpose | Avoid |
|---|---|---|
| Same start and finish events | Compare identical machine intervals. | Mixing post-processing with motion time. |
| Profile and exported file revision | Retain the configuration behind the estimate. | Comparing a new slice with an old observed job. |
| Pause and intervention duration | Separate interruption from ordinary timing bias. | Treating one delayed filament change as a universal percentage. |
Why does a small part ignore my high speed setting?
Short paths, acceleration, cornering and cooling can prevent the commanded speed from being reached or sustained.
Can STL volume give a reliable finish time?
No. Slicing, motion limits, flow, cooling and machine procedures are needed; geometry alone does not provide a justified duration.