Prioritize minimum layer time over external wall speed

[xokahag]

Is there an existing issue for this feature request?

• I have searched the existing issues

Is your feature request related to a problem?

Recently the feature "don't slow down external walls" was discussed (#5147) and merged (#5148). It greatly improves the outer wall finish and archives it much easier then slowing down inner layers manually, making it an easy default choice.

However if the model is small, slowing down the inside extrusions to the minimum specified speed might not be enough to archive the required minimum layer time. This problem is especially bad if there are only outer walls and if the outer wall speed is high to mitigate VFA. If layer times are not verified manually, the print may fail due to insufficient cooling.

Which printers will be beneficial to this feature?

All

Describe the solution you'd like

Rename "Don't slow down outer walls" to "Avoid slowing down outer walls". If slowing down inner extrusions is not enough to archive the minimum specified layer time, slow down outer walls anyway. This approach gives best quality wherever possible, while minimizing risk of print failure.

Bonus: If the layer time is too short despite slowing down all extrusions to the minimum specified speed, it's be great if a warning is shown to the user after slicing.

Describe alternatives you've considered

• disable "don't slow down external walls" and live with the worse quality, but minimize failure rate
• manually verify the sliced result, and edit the filament preset whenever needed. Changes apply to the entire model, so again worse quality for the entire print
• manually verify the sliced result, and add sacrificial print object so the slicer has more extrusions it can slow down. Best results, but requires print area and extra material

Additional context

I think and hope this should be a small change to the logic, but I am not skilled enough to do it myself.

Tagging @igiannakas because he submitted the initial PR. I decided to make a separate issue, because the original request was completed and I don't want to append more stuff.

Note: This is a repost of 6859, which should not be visible to you because github didn't like my account creation procedure.

[xokahag]

The original issue is now visible, so I'm closing this duplicate. See #6859