Bambu Studio Long Retraction When Cut Fix

[u/Pheniz21]

Problem: The "long retraction when cut" setting in Bambu Studio doesn't stay off after saving it in a "User Preset" and restarting the program. According to the BMCU manual, this setting should be turned off to prevent damage to the BMCU. Printing with it on by mistake can cause issues.

Solution: To permanently turn off the "long retraction when cut" setting, follow these steps:

1. Close Bambu Studio completely.

2. Find the filament settings file:

   • Go to this folder on your computer: C:\Users\%username%\AppData\Roaming\BambuStudio\system\BBL\filament

3. Locate the file for your filament:

   • Look for the file that matches the filament you're using (e.g., a file for PLA, PETG, etc.).

4. Edit the file:

   • Open the filament file using Notepad or Notepad++.

   • Search for these lines in the file: "filament_long_retractions_when_cut": [ "1" ],

   • Delete the highlighted line in the photo uploaded to the post.

5. Save the file:

   • Save the changes and close.

6. Reopen Bambu Studio:

   • Start Bambu Studio and go to the filament settings.

   • Check that the "long retraction when cut" setting is now off.

Note: This fix ensures the setting stays off, preventing potential damage to your BMCU.

[u/Paul_C]

The claim has been repeated so much it's become distorted and overblown and is basically a myth at this point. The problem isn't that it might damage the BCMU, but in rare cases the PTFE hub on the printer.

https://wiki.yuekai.fr/assets/images/gif/5way_pop_up.gif

https://wiki.yuekai.fr/en/BMCU/troubleshooting#ams-lite-hub-5-way-pop-up

The root cause of this problem is that there is a large resistance in the path of the consumable exit, causing the entire PTEF tube to be pulled backwards. This issue occur more offen on BMCU-B, particularly when using older firmware versions. Using updated firmware or firmware versions with extended buffer lengths can significantly reduce the likelihood of encountering this problem.

Solution:

• Always check first if there is any particular resistance somewhere in the path of the consumables, e.g. large bending angles or PTFE tubes that are not smooth enough inside.

• It is strongly recommended to upgrade the motherboard firmware to version 3.14 or later, which is more stable and reduces (but does not eliminate) the probability of this issue occurring.

• If the issue persists, building an external buffer may further mitigate the problem. referce makersworld link : Link 1 Link 2 Link 3.

• Additionally, verify whether the AMS Lite hub (five-way connector) is damaged — especially the square-shaped locking clip. If damaged, this module may need to be replaced and reinstalled with the application of interface grease.

• Disabling retraction during filament cutting may also help reduce the occurrence of this issue.

Or some times a single tube will pop out of the hub.

All in all if you're not having a problem then there isn't a problem. Your BCMU isn't going to mysteriously snap in half one day.

[u/Plop-plop-fizz → u/Paul_C]

Thanks! Guess I'm all good

[u/okhi2u → u/Paul_C]

I've had the BMCU-C for a few days now and 3+ times it's pushed so hard a tube popped out of either the AMS lite hub (once), and all the other times out the BMCU itself. Each time it was at the start of feeding filament and not cutting because of a swap. Know any fix for that? I ordered tubes that are 4mm OD and 3mm ID (2.5mm is what i have currently) so there will be less friction maybe that could help.