Hi All,
Hoping someone has some advice before I lose my temper! 
Long story short, I’ve re-arranged my ‘workshop’ so that my 2x AMS Pro 2 units and my 2x AMS HT units sit under my H2C. My workbench is approximately 1m high, with the H2C sitting on top of it. Bambu’s ‘suggested’ PTFE tube suggestions are either ballpark or very hit and miss. My 2x AMS Pro 2 units have PTFE tubes that run upwards into my H2C and are approximately 1.5m in length. They work fine. Occassinaly I will get resistance errors, but the filmanet always loads. Never a ‘major issue” and never a failed print or failed filament load.
My AMS HT’s however, are something else. No matter the length, I can’t get the filament to load. The filament reaches the toolhead/nozzle.. filament sits in the nozzle for a few seconds and then retracts back into the AMS HT spool. I cannot, for the life of me, get the filament to load. The PTFE tubes for my HT units are a shorter than for my AMS 2 Pro and wont work, but the longer tubes for AMS 2 work without issues?
I appreciate that the PTFE tubes cannot be an infinite length, however not everyone can have the same setup. Living areas, rooms and space where everything sits etc differs to each persons requirements, so having a suggested length of 900mm should not be a 1 size fits all. Especially considering how long my AMS 2 Pro tubes are and work no problem. Now, I havent been in the 3D printing game for long, just under a year to be exact, so I don’t know if this is by design and across all vendors or just a Bambu thing?
Anyhow, my small rant is over, so if anyone has suggestions on how I can get my HT’s to accept the filament, please let me know.
Thanks everyone!!
Place HT units on top of the printer and cut short PTFE feed tubes.
Test the filament feed into both feeds (in case one works and the other does not).
If success - adjust the tube longer until you find the sweet spot for your setup.
If fail - examine the HT unit.
I have two H2 Series printers and run AMS2PROs and HTs on both. Those stupid tubes can be really temperamental. And the external “assist” gadgets the BL released for TPU and such made them even worse (in my case). I just did the test posted and haven’t had an issue since. No idea why some are cool with longer tubes and some are a bit more restrictive. I run PLA and PETG only. So it’s really got nothing to do with filament. I considered running TPU on the H2 Series printers, but that got tossed when I worked with the external “assist” gadgets. Nope. I wish you the best. When they are dialed in, they are incredible printers. Worry free. Enjoy.
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I’m going to make a suggestion for you to consider.
It’s actually about timings. The printer asks for the AMS to provide filament, if the filament doesn’t present itself quick enough to the printer then the printer timeout.
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Hi Nic,
Appreciate the reply. I will give that a shot in morning. I may need to order more PTFE tubes, but if it ends up working then great. It’s really annoying me, because prior to my re-arrangning, the HT’s did actually work. Its just that I wanted to open my stacker without ripping the tubes out - new tubes with approximate same length dont work 
Hi Bionic,
Appreciate the reply. Yes, that does make sense, especially coming form an IT background.
Thought I do find it peculiar that my 2x 1.5m AMS 2 Pro tubes work - one could assume that the longer the tube, the longer the filament loading time and vice versa? Maybe I will try make the same length tubes as the AMS 2 and see what happens?
So you wouldn’t believe it.. To test, I disconnected my 1.5m PTFE tubes from my AMS 2 Pro and connected it to my HT. I then tried to load the filament (Support Material for PETG).. It worked!! 
What on earth! Just ordered more tubes from Amazon. Waiting for them to arrive later today and I will make more of the same length. Once everything is connected back like it was, I will confirm if all my AMS’s are working as they should
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Outstanding.
Yeah. Those stupid tubes will give you fits for sure. I ended up with a very specific sweet spot for one printer set and a different sweet spot for the other printer setup. Makes zero sense. But we do what we have to do with this tech. Sometimes a good set of sound dampeners, a blackout eye mask, and a white cane helps.
And now of course, ofter getting the tubes, it doesn’t work!! This whole hit and miss (sorry to say) crap with the PTFE tubes is really annoying me! (keeping the language PG). I’ve cut them to same length that works on 2x of my AMS Pro 2, but nothing on the HT’s. Now, I dont want to blame Bambu if this is an industry thing, but damn.. it cant be just in the stab in the dark as to what length will work, what wont, some working with different lengths and not with others, one length works for 1 person and not another….DAMN!!
Yes indeed.
I had to come to the place where I understood that each of these is a bit of a custom length thing. I had to find that sweet spot for each printer/AMS so that they all flowed smoothly.
Imagine the fun when I thought I had the testicular fortitude to add the Filament Assist gadget to these. What a fun time. I ended up placing them safely away next to the TPU gadgets. Nope. Not in this house. I can print without them just fine. Zero limitations. And don’t my PTFE tubes look nice. And that filament flows smoothly with my custom tube lengths.
Unfortunately that’s the real story. You need to take the time to find “YOUR” specific printer setups sweet spots. It can be different for us - as evidenced by the responses in threads similar to this. The variance tells the tale.
I wish you the best. PTFE isn’t expensive. It’s worth the time and effort to find where yours flows smoothly.
Nic,
That argument presumes that all components work the same. That is, one AMS will function exactly like another built the next day, but there will always be variation between the same products. The question is, how much variation is normal or factory acceptable? Are there escapes where some products might exceed a factory acceptance test before shipping out?
Then there might be environmental differences or filament differences. It can get pretty ugly pretty quick.
Perhaps you misunderstood?
I am saying very clearly that these do NOT act the same. In fact, they act a bit different depending on which printer I connect them to (perhaps due to the positioning for that setup in my particular space).
It is without a doubt a very different length of tube for different setups. They have different angles, different bends, different filament needs, different placements, etc etc etc. And those factors will inevitably provide for a fun and all consuming time with the PTFE tube length cutting dance.
Again, I wish you the best on this. It’s not cut and dry - it’s more of a cut and test, cut and test, cut and test. hahaha
Take care.
I’ve found that not all PTFE is created equal. I was buying cheap stuff off of Amazon with limited success. Now I just buy it direct from Bambu and I no longer have issues. This is my setup. Two AMS 2 Pros each on the right nozzle, and two AMS HTs each on the left nozzle. No feed issues.
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I am not sure where this stand but just wanted to point out that t = d / s. The toolhead timing out may not be a result of the length being the same. You have to consider speed, as well.
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Juuuust in case… when I cut PTFE tubes I have learned that it’s really important that the end be cut square, not on an angle, and to use a sharp razor for the cut, not scissors. Scissors will tend to make the cut end pinch into an oval shape that will catch filament. Angled cuts may not sit flush to the fittings and create a point where filament can hang up on a crack.
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I got one of those when I ordered a bunch of PTFE tubing. It seems to cut nicely.
Hi Kerwin,
Firstly.. love the setup!! 
If I may, how long are your PTFE tubes from your AMS? (roughly)
My setup is similar to yours, except my AMS units sit under my printer with filament feeing upwards.
Not sure if thats contributing in any way, but it is annoying me!
Yes, I did buy my tubes from Amazon.. so I am happy to purchase form Bambu to get my setup to work, but I am not sure how or why that would causing my issues?
Hi Void,
I can understand, but surely one would not make the speed differ from a HT to an AMS Pro?
I could see that causing a magnitude of issues if that was the case? But.. perhaps I am wrong.
I’m open to suggestions, as this is driving me crazy. Surely it cannot be that hard
Bambu PTFE’s have a 2.5mm inner diameter.
When looking for PTFE’s for 1,75mm filamemt on amazon, quite a few 2.0mm inner diameter PTFE’s pop-up. Those will not work well due to the increased contact area and hence friction.
& 
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Hi Eno,
Appreciate the reply.
I did check that the Amazon ones I purchased are 2.5mm, but hey.. who knows.. they may not be as described. I did end up purchasing Bambu PTFE tubes, so I will have to wait till the arrive to test. I am crossing my fingers on this that it works, as it really is starting to annoy me that I can’t use my HT’s correctly
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