TPU Nozzle Jams randomly  

RE: TPU Nozzle Jams randomly

Update, it happened again - the extruder itself keeps spinning, but no filament comes through... It didn't seem tremendously hot or warm on the filament where the teeth of the gear were...

RE: TPU Nozzle Jams randomly

I usually don't use "TPU" and " print fast " in the same sentence.  I have a hard time believing those videos. Sure, I can print TPU at 200 mm/s… for 5 seconds.  It is rubber after all, so in my simple view of the world that means the gears don't get a consistent grip on the filament, which gets exacerbated at higher speeds. 

RE: TPU Nozzle Jams randomly

Fair enough yeah I wouldn't put too much weight behind the video - but it is possible to print faster - there are printers out there (including this one!), that can consistently print TPU above 20-25mm/s - I'm pretty sure the official docs say it should be able to go up to around 40mm/s.

So there still must be a limiting factor here somewhere which I can resolve - even if I have to modify the printer, that's fine by me, but a fundamental understanding would be so useful!

When I print slower, at around 10-15mm/s, it never jams. When I increase the speed, I get these rare jams.

Unless the print is extremely simple you will have potential issues whenever detail and straight runs follow each other and the nozzle pressure has to change, TPU is so elastic that pressure changes cause variations in the mass in the melt zone that must be allowed to equalise if printing is to be a success.

Basically I want to know fundamentally why my print is failing so I can take action to fix it! Is it the idler is still too tight and it's crushing the filament? Is the extruder getting too hot and melting the filament?

No, you're fighting the physics of the filament,

Is it caused by inconsistent diameter filament? etc...

As you push/pull the filament it changes diameter dynamically.

With a general printer like the i3 rapid flex filament printing will only work with a very limited range of prints.  If you want to print a lot of TPU then a second printer is the easiest way to increase output.  You might want to investigate a specialist Flex printer if it's really important, they do exist but they're not cheap.

Cheerio,

RE:

I appreciate the response!

But forgive me, I still can't entirely believe that it's a fundamental limitation of the filament for a few reasons (that's not to say there isn't a ceiling to the speed you can print due to the physics of the material, but more that I haven't hit it yet at 20mm/s).

You say that there are specialist flex printers out there - meaning that you can do it faster and more reliably (otherwise what other purpose do they serve!), so what is it that they do differently that the Prusa doesn't? Surely theres some modifications I can do to atleast make the print somewhat more consistent.

My goal here is not to reach 200mm/s, but maybe 30mm/s, or 40mm/s - or even just to make it not jam at 20mm/s. The print I'm doing is quite simple. A simple shape, with about 65% infill, and some cylinders on top - I wouldn't have thought I'd be pushing the limits of the printer here.

Another thing I've heard is that does a larger nozzle help? I've seen that they tend to jam less - is this different to what's happening with the flex though as is it getting stuck in the extruder assembly? Could I turn off the default retraction profile settings to make it less likely to jam there?

I hope I'm not coming across as dismissive or anything, it's not my intent! But I struggle to believe that there's nothing I can do based on other threads I've seen to stop my printer jamming so often.

RE:

If you feed the filament too fast, the increasing pressure will cause the filament to bend directly below the gears in the extruder and cause a jam, temporarily if the pressure does not build up further or permanently if the bend filament gets stuck above the PTFE. This is normally a function of the volumetric flow rate, you just can not feed the filament faster than the hot end can melt with the pressure the filament can withstand without bending.

If you want to time optimize your TPU print I would just use default speeds and set the max volumetric down to around 2 (and by that limit the print speed of everything with the relevant parameter) and then slowly increase the value until you get the failures. This way you find the limit for your TPU.

RE: TPU Nozzle Jams randomly

The standard profiles in Prusa Slicer for flex filaments are quite conservative concerning speeds. For instance, Fillamentum Flexfill 98 max.vol, speed is by default  1.35 mm3/s. Printing with a 0.2 layer height and 0.4nozzle (extrusion width=0.45mm) that’s : 0.2x0.45= 0,09mm2. This is the section of the strand of filament that the hotend is laying.

Therefore, at 1.35mm3/s vol speed, you can print up to 1.35/0.09 = 15 mm/s. No matter which speed values you set for perimeters, infill, etc.  you can’t exceed 15mm/s,  Raising the max vol speed to 2.0 then you’d have 22.2mm/s max, linear speed.  I wouldn’t go faster than that with TPU95/98, even less with softer materials, but everybody is free to experiment. Temperature also plays a role here.

You say that there are specialist flex printers out there - meaning that you can do it faster and more reliably (otherwise what other purpose do they serve!), so what is it that they do differently that the Prusa doesn't?

There were some at TCT3Sixty.  I didn't pay a lot of attention as my current interests differ.  I believe the filament handling has to be a lot different, larger diameter feed wheels and short, higher powered melt zones but Icbw.  Visit one of the larger shows and see for yourself.

Surely theres some modifications I can do to at least make the print somewhat more consistent.

If you are printing many of the same, or lightly customised, parts then you may be able to tweak the gcodes so that simple sections print fast and tricky ones print at lower speeds.

Cheerio,

RE: TPU Nozzle Jams randomly

I am using 2 year old tpu from overture and dont yet have a problem. I think its printing at 45mms. One of the things I did was loosen the gear squeeze on the filiament.

RE: TPU Nozzle Jams randomly

Just want to post on this thread with an update - I wasn't fighting the physics of the filament, I was fighting mainly moisture, and resistance from the spool.

I bought myself an eSun filament dryer which you can feed directly from - and now I'm printing at 15MVS (30+mm/s), and I haven't yet reached the limit.

I'm also using a 0.6mm nozzle to allow for slightly faster printing too. TLDR, you can print flexible fast on a Prusa - and consistently too, it's actually surprisingly failed less than printing slowly!

RE: TPU Nozzle Jams randomly

I'm utilizing 2 year old tpu from suggestion and don't yet have an any issue. I believe its printing at 45mms. Something I did was slacken the stuff press on the filament.