Summary

What is it?

This mod for the Bambu Lab AMS enables the use of TPU (tested down to 85A) while maintaining compatibility with standard AMS-supported filaments. It opens up the possibility of printing TPU parts with complex geometries using support materials, as well as multi-color TPU prints.

Who is it for?

For people who want to print flexible materials and are willing to tinker with it and aid in further development. This is a work in progress. I have tested it extensively on my printer, but I can't guarantee that it will work for you. Your feedback will help me improve the design.

Is it reversible?

Yes, this mod is 100% reversible. There are no changes to your printer or AMS that can't be reverted. If, for some reason, it doesn't work or you're unhappy with it, you can go back to your old setup in a matter of minutes.

Limitations

This mod currently only works for nozzles ≥ 0.6 mm, and the AMS needs to be placed next to the printer in an elevated position. I guesstimate that the reliability is around 98% for me, which is not quite as good as the standard AMS.

__________________________________________________________________________________________________________________

Warning

While this mod is fully reversible, Bambu Lab may still consider your warranty void, as stated on their website/wiki. Proceed at your own risk.

How does it work?

There are three main reasons why the standard AMS can't handle soft filaments:

• The filament slot spring is too stiff to allow soft filaments to retract
• The filament hub spring is so stiff that there is not enough resistance created by the flexible filament reaching the extruder for the gears to start slipping. If the gears don't slip the hall sensor doesn't send a signal to stop, so they just keep turning indefinitely and start shredding the filament to bits.
• The standard tubing is too long and has too many curves, which causes the filament to either not reach the extruder at all, not have enough force remaining to actuate the filament buffer, or not have enough force to overcome the filament sensor inside the extruder.

These issues can be solved by using custom springs and adjusting the filament path.

Instructions

1. Print the travel stop and the hub spring both in TPU 85A (I used Extrudr Semisoft TPU). 

Edit: I've been informed by two users that 95A TPU works as well. I will test that when I get around to it.

2. Replace the metal springs with your new printed springs/travel stops as shown below.

3. Get two pieces of standard Bambu Lab PTFE tubing (2.5 mm inner diameter, 4 mm outer diameter) with a length of 40-45 and 55-60 cm. 

The longer piece goes into the extruder and the shorter one into the AMS. Remove the buffer from the printer and connect the two pieces of tubing through the buffer. Put the AMS in an appropriately elevated position, so that the tubing has enough slack for the buffer to actuate. Avoid using the Bambu tube connector pieces, as they narrow down to a straight edge on which the filament can catch and cause malfunctions.

4. Done!

5. Try to run the 100x filament change test. You should get less than 5 errors per 100 filament changes and they should only occur on TPU. If you have any failures with filaments other than TPU, something is wrong!

Things to watch out for:

• If you aren't already, use a filament guide. I use this one, but I'm sure others work too. Without a filament guide you might get filament caught on the edge of the filament sensor.
• Make sure that the tubing that enters the buffer can travel freely. If it rubs against the guide hole the resistance can lead to failures to feed TPU. If you can't solve the issue by adjusting the tubing, you can print the optional buffer housing. It has a large opening on the spring side and no guide hole.
• If the AMS filament slot has trouble feeding the filament towards the hub, it means that the travel stop is undersized. Scale it up in the Z-direction by 0.5 mm and try again (happened to me on one slot)
• Remember, TPU gets soft at elevated temperatures. Run your printer with the door and/or lid open.
• TPU has a hard time purging other filaments - adjust your purge ratios accordingly!

Roadmap

AMS position

Currently the AMS has to be placed next to, or behind the printer to keep the filament paths short, and relatively straight. I did try to put the AMS on top of the printer, but then the tubing was either too long for the filament to have enough force to feed, or it was curved to a point where the buffer couldn't properly actuate. If the 4 pin bus cable that connects the printer with the buffer was a bit longer, you could adjust the angles appropriately. Unfortunately, as of me writing this, I haven't been able to find a longer version of this cable yet.

0.4 mm nozzles

This mod was initially developed with the standard 0.4 mm nozzle, but the backpressure during purging caused the TPU to be deformed by the extruder gears, which later led to failures to feed. Additionally, purging didn't work properly for the same reason, which caused frequent nozzle clogs. I tried to remedy this problem with custom G-code, but since I'm not very experienced I couldn't come up with an appropriate solution. If you have an idea for custom G-code and some time to spare, please contribute!

Purge routine

The current purge routine works, but it isn't pretty. Because it is necessary to purge quite a large amount of filament when changing to TPU, the purge piles up in the shute and it forms a blob around the nozzle. 

Maybe someone could write some G-code that wipes off the purge half way trough the routine, instead of just at the end.

Another possible solution would be to use custom G-code that reduces filament waste, as shown here, but I haven't been able to test that yet.

This project was inspired by a video by Noozle3D on Youtube. I would also like to thank the members of the X1Plus discord for providing valuable feedback.

Changelog:

19.06.24 Re-uploaded the hub spring model. Due to an error I made in CAD it was modeled as three parts that could be split by the user.

12.06.24 Initial release