AMS Filament Guide

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Bambu AMS Feeder Funnel Cap | Angled PTFE Wear Fix

Compact PTFE Solution for Worn AMS Feeder Funnels

After many development iterations and extensive real-world testing, this design became the final version of my AMS feeder funnel repair solution

I originally started developing these solutions entirely from scratch to solve problems I personally experienced with worn feeder funnels in my own AMS units

Earlier prototype versions already worked reasonably well, but some still had weaknesses in certain situations. During development, I continuously refined the design step by step until the remaining issues were eliminated

The main goals were always:

• reliable filament feeding with full and nearly empty spools alike
• no spool jumping or unstable spool movement
• no AMS disassembly
• no feeder unit removal
• compact and clean design
• simple installation
• stable and secure PTFE tube mounting
• long-term reliability

The Actual Problem

Over time, the original AMS feeder funnel wears down from constant filament contact

Grooves form inside the plastic funnel, allowing filament to catch or bind during fast feeding and retract movements. During aggressive AMS movements, this can overload the helper motor and cause failed prints

The problem is that the funnel itself is not officially replaceable separately

That means:

• the complete feeder unit normally has to be replaced
• the AMS contains four feeder units
• replacement costs can add up quickly
• even though only a tiny plastic funnel is actually worn

This solution was designed specifically to avoid that

How This Solution Works

This repair cap presses directly onto the original feeder funnel

A short PTFE tube is then screwed into the integrated angled channel and guided down to the actual filament entry point

Instead of running across the worn plastic funnel, the filament now runs smoothly through the PTFE tube

This completely bypasses the damaged funnel area

The solution also works when the original funnel is already visibly worn or grooved

The original feeder funnel does not need to be replaced

Why The Angled PTFE Channel Matters

One of the most important improvements of this final version is the intentionally angled PTFE channel

Many simpler solutions only add a vertical PTFE guide. During my own testing and earlier prototype phases, this turned out to create problematic filament pull angles once spools became nearly empty

As filament rolls empty, the filament increasingly pulls toward the center of the spool. With vertical PTFE guides, this can create upward leverage and pulling forces on the spool itself

This may lead to:

• spool hopping
• spool lifting
• unstable filament movement
• increased feeding resistance
• pressure against the AMS lid
• or even the spool partially jumping out of position when the AMS is open

This final version solves those problems by using a PTFE channel intentionally angled toward the spool

The angled filament path creates a much more natural filament entry and exit angle while significantly reducing unwanted upward forces acting on the spool

After extensive long-term testing with:

• full spools
• partially used spools
• nearly empty spools
• and almost depleted rolls

this final version no longer showed spool jumping, lifting, or unstable spool behavior

Filament feeding remained smooth and stable throughout testing

Important Design Details

Several additional details were optimized during development:

• the feeder button remains fully accessible
• the beveled housing shape does not interfere with filament insertion
• the repair cap sits securely on the original funnel
• the PTFE tube is threaded into place instead of loosely inserted
• the shorter threaded section improves installation handling
• the compact shape keeps the setup clean and unobtrusive

Installation

The PTFE opening was intentionally designed with a very tight tolerance

The PTFE tube is not meant to be pushed straight in loosely

Instead:

• gently press the PTFE tube against the opening
• slowly twist the tube into place

The tube is essentially screwed into the channel, creating a very secure fit without additional fasteners

Because the threaded section is shorter than in earlier versions, the PTFE tube no longer needs to be bent during installation

Important PTFE Depth Notice

The PTFE tube should extend approximately 2–3 mm below the printed part

If the tube is screwed in too deeply, the lower end may compress slightly inside the funnel area

This can:

• increase friction
• reduce feeding quality
• or make filament insertion more difficult

If filament becomes difficult to insert, the PTFE tube was most likely screwed in slightly too far

Recommended PTFE Tube Length

After additional testing, a PTFE tube length of approximately 3–4 cm turned out to work very well

This length keeps filament movement stable while reducing mechanical stress on the spool

Whether much shorter or longer tube sections work equally reliably may depend on the individual setup

If the tube turns out to be too long, it can simply be shortened and tested again

Currently recommended:

• approximately 3–4 cm PTFE tubing

Advantages of This Solution

• No AMS disassembly required
• No feeder unit removal required
• No tools required
• Works even with already worn funnels
• Stable filament feeding
• No spool jumping with nearly empty spools
• Very compact design
• Extremely secure PTFE tube fit
• Fast installation
• Very inexpensive
• Wear parts are easily replaceable

Required Parts

• Printed model
• PTFE tubing (recommended: 4 mm outer diameter)
• Scissors, side cutters, or hobby knife

Recommended PTFE dimensions:

• 4 mm outer diameter
• 2.5 mm inner diameter

For example:

• Bambu Lab PTFE Tubes
• Product ID: FAT001

Filament Recommendations / BOM Notes

The filaments listed in the BOM are simply recommendations for achieving especially good print quality, attractive surfaces, and matching colors

The model will also work perfectly with many other filaments

Please note:

Some recommended filaments are available both as regular spool versions and as “Refill” versions

Refill filament does not include a reusable spool and requires a compatible refill spool system

If you do not already own compatible empty spools, you should avoid ordering refill versions

Compatibility

Originally designed for the first-generation Bambu Lab AMS

However, the general concept may also be useful for other AMS systems or filament feeding setups

Disclaimer

This is a community-made solution and not an official repair from Bambu Lab

Installation and use are entirely at your own responsibility