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I want to end the bed heating approximately X minutes before the print is finished so that the bed starts cooling and releasing the print.

Since an object can have different sizes and printing one layer can take very long or very quickly, I cannot simply insert an M140 S0 before the last layer. What is the best time interval and method to achieve this? Is there a Cura slicer extension for it, an OctoPrint plugin, or should I write a custom script for Cura? I mostly print with a 50 °C heated bed and PLA using OctoPi on a Creality Ender 3 v2 with Marlin firmware. With a printer bed at room temperature, the print could come loose too early while still printing, so 20 °C might be too extreme. Make sure the printer is finished when the bed is around 35-40 °C? Is there any theory and method to back this up? Does this method have a term or name?

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    $\begingroup$ Nice energy-saving idea. Similar to turning off the (electric) oven or ring ten minutes early, to allow the residual heat to continue the cooking. $\endgroup$
    – Greenonline
    Commented Nov 1, 2023 at 14:52
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    $\begingroup$ That's another added benefit indeed. Although micro optimizations, this probably could also save some energy: 3dprinting.stackexchange.com/questions/21565/…. $\endgroup$
    – Bob Ortiz
    Commented Nov 1, 2023 at 15:02

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You barely save energy keeping a plate warm a few extra minutes, certainly with an insulated bottom. It will not cost much electricity. This has been seen before in various answers.

The chance the print releases increases with stopping heating the bed and increases the chance to mess up the print requiring a reprint. This will add frustration, filament costs and energy costs. Best interval is therefore zero (based on experience with printing on glass, at a certain temperature the print comes free from the build plate on glass). But, different surfaces may hold the print even when cold. E.g. PETG on PEI bonds very well.

If you really want to stop heating the bed, you need to determine for a few various sized prints the point at which the print releases. Based on your tests you could device a strategy to stop heating the bed.

If you want to release a print sooner after printing, get a removable build plate, e.g. a flexible coated steel plate or a few sheets of glass and place the print with glass in the fridge or somewhere where it is cooler.

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  • $\begingroup$ The energy saving, as mentioned in the comments, is of least concern. Do you know of an existing implementation of this strategy (in OctoPrint, Marlin or Cura)? $\endgroup$
    – Bob Ortiz
    Commented Dec 11, 2023 at 17:58
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    $\begingroup$ @BobOrtiz No I don't know of such implementations, that doesn't guarantee it doesn't exist, but I think it doesn't exist for these exact reasons. $\endgroup$
    – 0scar
    Commented Dec 11, 2023 at 18:35
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In addition to Oscar's answer, there is an OctoPrint plugin that attempts to achieve exactly that. The plugin uses the following and-condition to determine the moment to stop bed heating:

"printing finished for at least 90% and remaining print time is below 5 minutes".

The plugin is called OctoPrint-BedCooldown. Its page describes:

Turns off the bed heater toward the end of a print

For filaments such as PLA, many printers have more than enough stored thermal mass in the bed to keep bed adhesion throughout the print. Therefore, you may want to turn off the bed heater automatically before the end of a print, saving cooldown time.

The bed heater will be turned off during a print, when both conditions are met:

  • The print time left is below the configured threshold (default 300 seconds / 5 minutes)
  • The print completion percentage is above the configured threshold (default 90%) This should cover both long and short prints; you wouldn’t want the bed to turn off 90% into a 20 hour print, or 5 minutes before the end of a 10 minute total print.

Be sure to monitor your print, as turning off the bed heater could cause the print to come loose prior to completion.

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    $\begingroup$ Nice find, but Ill refrain from using it! 😃 Considering the caveat at the bottom, be careful! $\endgroup$
    – 0scar
    Commented Dec 19, 2023 at 10:24

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