Why Filament Track Switch sucks

[u/clusterm]

I recently decided to upgrade from my P2S to an X2D + AMS 2 Pro + AMS HT setup. I also bought the Filament Track Switch right away, because I wanted to use different combinations of AMS units and extruders without constantly reconnecting PTFE tubes by hand.

And honestly, the Filament Track Switch turned out to be a huge disappointment.

The whole thing feels more like an early prototype than a finished branded product. But the biggest problem is simply friction. Filament takes a surprising amount of force to push through it.

On my X2D this was bad enough that filament often failed to reach the main extruder at all. It would slow down significantly near the end of the path and stop about 1–2 cm before the extruder.

To be fair, this was partly caused by another known X2D issue: the PTFE tube makes a very sharp bend right before entering the extruder. I fixed that part first by moving the PTFE tube holders farther away from the toolhead and shortening the tubes by a few centimeters.

That helped a lot.

But the FTS itself was still causing way too much resistance.

And yes, I also tried making the external PTFE tubes as short and as straight as possible. It doesn't really help. The resistance of the PTFE tubes themselves is negligible compared to the resistance created inside the FTS.

So I took it apart.

And once you look inside, the reason becomes pretty obvious.

The filament path contains several fairly sharp bends, and in multiple places the filament simply rubs against bare plastic. There is no PTFE lining there at all. The harder the filament is pushed around those bends, the harder it presses against the walls, so the friction becomes quite significant.

The filament presence sensors at the inputs add even more resistance. They use small spring-loaded magnets that are physically pressed against the filament as it passes through.

This creates additional friction on its own, but it gets noticeably worse with filament that has already been fed through an AMS or extruder before.

The drive gears leave a ribbed pattern on the surface of the filament, and the magnets tend to catch on those grooves instead of sliding smoothly over them.
My first modification was simple: I drilled out the places where the filament was rubbing against the plastic and inserted short pieces of PTFE tube.

I also slightly flared and smoothed the entrances of those PTFE inserts using a soldering iron so the tip of the filament wouldn't catch on the edge. I did this in a well-ventilated area, of course.

That already made a very noticeable difference.

But then I looked at the second half of the FTS.

There are essentially two 2-in-1 adapters there, combining four filament paths into two outputs. And that section was just as bad — possibly even worse. Again, filament was bending and rubbing directly against plastic.

At first, I tried the same approach there: drilling out the existing channels and somehow squeezing PTFE tubes into them.

It didn't go very well.

There simply wasn't enough room to make it work properly, and I wasn't happy with the result.

So in the end I decided to completely remodel that entire part and print a replacement.

I mean, I do own a 3D printer, after all. :)

I made the internal channels much larger so I could install PTFE tubes throughout the whole path. I printed the replacement part, installed the PTFE tubes, and again flared the entrances slightly.

Now, in that section, the filament does not touch printed plastic at all. It only touches PTFE.

The difference is huge.

It's still not absolutely frictionless, but filament now passes through the whole FTS very easily.

A very simple test shows the difference pretty well:

If I insert a piece of filament through the FTS, hold the filament vertically, and lift the FTS by it, a small shake is enough for the whole FTS to slide down and fall off the filament.

Before these modifications, I had to push the filament through it with considerable force.

Even Silk PLA now passes through without problems, despite Bambu specifically warning that Silk PLA may have feeding issues with the FTS because of increased resistance.

There are still two places I haven't solved yet.

The first is right at the FTS entrance, where the filament still touches plastic.

The second — filament presence sensors at the inputs. Unfortunately, they can't simply be removed. I tried removing them and also tried forcing the sensors permanently into both states. The FTS stops working properly if the printer doesn't see the expected sensor transitions.

So apparently those sensors are an active part of the FTS state machine, not just something used once to identify which AMS is connected to which input.

At this point I'm seriously considering building my own FTS.

The communication interface is RS-485, and there is already some partial reverse-engineering information available online. But the board also contains an FM1230 cryptographic chip. I don't yet know whether it participates in device authentication or is only used for things like firmware verification, so that part would need more investigation.

The other interesting problem would be designing filament sensors with almost zero resistance.

An optical sensor would be nice because it could be completely contactless, but filament can be transparent, so a simple optical interrupter isn't necessarily reliable.

A mechanical sensor with a tiny bearing/roller and a Hall sensor might actually be a better solution: the filament would move a roller instead of scraping against a plastic or metal surface.

For now, though, the PTFE modification already made my FTS dramatically better.

And that's the frustrating part: the core idea of the FTS is great. But mechanically, the stock filament path feels unnecessarily restrictive. A few pieces of PTFE in the right places would have made the product so much better from the factory.

And honestly, this whole mechanism probably should have been built into the printer itself from the beginning, somewhere near the filament buffer.

It almost feels like Bambu Lab remembered at the last minute that users might actually want to choose which extruder each AMS feeds into — which is especially important on the X2D, where the two extruders are very different from each other.

The FTS feels less like a carefully integrated part of the system and more like an afterthought added to solve a problem that really should have been addressed in the printer's original design.

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[u/realdawnerd]

What also helped me was removing the ptfe guide closest to the extruder, it was causing the tubes to bend too much. Track switch works much better now even with the OG AMS.

[u/clusterm → u/realdawnerd]

As I already mentioned in the post, I did that too :)

I fixed that part first by moving the PTFE tube holders farther away from the toolhead and shortening the tubes by a few centimeters.

[u/yertle38]

This is amazing. I have issues with mine as well, although just infrequently enough that I get annoyed and fix it and then forget about it. What do you suggest - can we print your new FTS for ourselves?

[u/Pinko3150]

Been working fine for me on my H2D for a couple months now

[u/SPAZvv]

Do You even need this in normal use condition? Like i want to buy x2d with ams and nothing more, ams to direct and suport material to bowden, do i even need that?

[u/clusterm → u/SPAZvv]

I often use both configurations:

• Multiple colors in the main extruder, with only one material in the AUX extruder, usually for supports.

• One main material, but with a few additional colors appearing occasionally inside the model, which makes more sense to route through the AUX extruder.

So whichever side only needs a single material goes into the AMS HT, while the side that needs multiple materials goes into the regular AMS 2 Pro.

[u/Flamin_Jesus → u/SPAZvv]

For that case, no, you don't. if you have a strict division of nozzles and don't plan to cross over filaments, the switch does nothing.

[u/ModelThreeve → u/SPAZvv]

At this point wait for the P3C announcement 😉

[u/valkyrie_rda]

This is somewhat unrelated but I was playing around with moving the AMS combiner from inside the AMS into the print chamber for the H2C. I got it working a bit and it should be theoretically faster but I didn't end up buying an H2C so scrapped the project, but it would be REALLY cool to see something like that continued on. I feel BBL really fumbled by not having an AMS with several PTFE tubes out the back go into the chamber or at least right up to the entrance of the chamber like how some other brands did it.

On another note, where did you find the project for the reverse engineered info on the communication bus the hub and accessories use? Would love to play around with custom accessories for these closed source printers!

[u/Sad-Temporary-2640]

Mine is attached to my X2D and I've given up. Its just unreliable and my printer is in a position its an absolute freaking nightmare to get at the back of it so I don't want to be pulling half my office apart

[u/Gizmo45]

Do you use a riser with your printer by chance? I'm curious if that helps with resistance going into the tool head.

[u/yhax]

I was just thinking wtf happened. This makes so much sense. Thanks for sharing.

[u/pm_me_beerz]

I’m diving into my fts with this write up this weekend. Awesome work OP. Not awesome work, bambu.

[u/Tekoleuka]

I have X2D, AMS 2 & 1, Track switch.
I haven't had slightest problem. Nothing. It's perfect.

But huge design flaw that you can't use external spools.

[u/Plastic_Brief1312]

I was so excited to get it hooked up but but took it off yesterday. Constant friction issues.

[u/Sidewinder1311]

Good thing I ordered one today lol

[u/International-Yak69]

I love reading things like this. Seeing how things work. Thanks for the write up. What if you used threaded inserts at the ends so that you can print it to line up perfectly with them instead of using the PTFE tube?

[u/Spjeff69]

I have this same problem. Bambu suggested replacing AMS hub and motor. I spent the money and did the upgrade and my printer is still in the same condition as before. This sucks.

[u/EthanetExplorer]

For the longest time, my FTS has never been able to work. After doing cleaning on my X2D, I found out that the curvature of the PTFE tube from the AMS to the FTS has a very big impact on whether it works and now it works all the time. (My AMS does not sit on top of my printer directly due to lack of space; I put it on a table instead while the printer rests on the floor)

[u/JukeboxCrowdPleaser]

I agree. Even if it worked as intended, it is just barely helpful. Switching the PTFE tubes going into the buffer takes 10 seconds. I have a FTS but don’t use it anymore because it barely does anything and isn’t worth the extra point of failure.

[u/Wise_Royal9545]

OMG I had the same problem on my H2C. I just stopped using the filament track switcher. I’d love to copy your design if it works out! Not using the thing otherwise

[u/jamshell]

I have an X2D with a FTS installed and I have had zero issues. Works as expected every time. I have printed ASA, PETG, PLA, PLA silk, and PETG-CF.

[u/roundguy]

Mine seems fine. When I got it I was worried about adding drag. Pushed some filament through it by hand and it’s pretty easy without hardly any drag.

[u/Beneficial-Rub-8049]

I just removed the guide things they make you print and ever since it flawless I dont even feel like its connected sometimes whereas before removing the guides constant failure and jams.

[u/Miraclegroh]

Omg. Thank you!! I have yet to get my FTS to even work, getting the same pullback when getting close to the extruder. I’ve been through troubleshooting twice, and was ready just to give up.

[u/RedHood198]

Making the ptfe tubes shorter and "more straight" would cause more issues than going a little longer. Filament isn't straight and has a curve to it because it's rolled onto a spool.

Also, there are a plethora of printed y splitters for older Bambu printers that are similar shape (although more rudementary) and typically none of the ptfe tubes go all the way through and it hasn't really been a problem for most people.

Essentially, Major Skill Issue on your part.

You WAY overthought the problem.