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I recently heard that the 3D printing lab at my college can do fused-deposition with ABS and PLA, but I would like to use TPU, for greater flexibility.

Is it possible to feed a TPU filament into the same machine built for ABS/PLA? Or is there no difference? Assume the diameters of the filaments are the same.

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  • $\begingroup$ Are you referring to fuse TPU to ABS? $\endgroup$ – 0scar Jun 7 at 21:44
  • $\begingroup$ @0scar No. I meant if the same machine can be loaded with any filament. $\endgroup$ – William R. Ebenezer Jun 8 at 6:46
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Is it possible to feed a TPU filament into the same machine built for ABS/PLA? Or is there no difference? Assume the diameters of the filaments are the same.

The question is not what the machine is built for but how it is built. Let's break stuff down some into why some filaments work better than others and the challenges with them.

Temperature range

The first obstacle is the temperature range of the printer. For example, if your printer's Extruder can't get over 220 °C, you can't print ABS. You need to make sure your printer can match your intended filament's temperature range.

TPU usually prints around between the same temperatures for PLA and ABS, so it should work from that range.

Heated Bed

Most Filaments work better with a heated bed, but some are almost impossible to be printed without. For TPU, a heated bed should be used but is not absolutely mandatory.

Heated Chamber

Some filaments can't be printed without a heated chamber, others like ABS highly benefit from it. TPU is ambivalent on this as far as I know.

Extruder Setup

There's basically 3 extruder setups. Pellet extruders are super rare, so we don't concern about them. The other two are Direct Drive and Bowden. In a Direct Drive, the extruder motor is right over the hotend, and pushes the filament directly into it. In a Bowden setup, the hotend and the extruder motor are connected via a Bowden tube. Both have benefits and drawbacks:

A Bowden makes for a lighter carriage, leading to faster printing speeds. A Direct Drive has much less trouble with elastic filaments and can do much better with retraction.

TPU is one of the filaments that works much better with Direct Drive.

Other considerations

Some Print services do print in machines set up for one filament type and that only, because it prevents cross-contamination of the nozzles, especially when a high-temperature print material remains in it when a low-temperature print comes next. Having for example a little bit of ABS left in a printer that runs PLA next can lead to very very extreme clogging.

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    $\begingroup$ While TPU prints best at ABS-like temperatures (lower viscosity), you definitely can print it at the higher and of PLA-like temperatures, and maybe even the mid to low end. I get decent extrusion even under 200°C but I haven't experimented with how good the adhesion is. $\endgroup$ – R.. GitHub STOP HELPING ICE Jun 8 at 17:24
  • $\begingroup$ @R..GitHubSTOPHELPINGICE good point, I think it's best to say TPU is "between" PLA and ABS in temperatures then. $\endgroup$ – Trish Jun 8 at 18:20
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Regarding your particular question about TPU, any machine that can print PLA should be able to print TPU. Bed temperature is even less of an issue, and the needed nozzle temperature is roughly the same. The only potential difficulty is that, if the entire path from the extruder gear to the hotend isn't tightly confined, the soft filament can kink rather than advancing properly. However, this isn't a show-stopper - it can almost always be solved with printable upgrades to constrain the path.

If your printer has a bowden extruder, you have to go pretty slow with TPU because there's so much room for the filament to compress between the extruder gear and the nozzle, making the response to extruder advancement and retraction lagged. But this can largely be solved by upgrading the printer's firmware to one with "linear advance" or "pressure advance" feature that compensates. I can print TPU very well at 30 mm/s on my Ender 3 with firmware upgraded to Marlin 2.0, with a whopping 5.0 as the linear advance spring constant.

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Most printers can print most filaments. However, some more exotic filaments are not suitable for all printers:

  • To print a flexible filament such as TPU, the filament path from the extruder needs to be well-constrained. A bowden extruder is generally less good at handling flexible filaments than a direct extruder. Some direct extruders without a well-constrained filament path may also be unsuitable.

  • A printer without a heated bed won't be able to print filaments that tend to warp such as ABS.

  • A printer without a (heated) enclosure won't be able to print filaments that tend to warp a lot such as polycarbonate

  • A printer with a PTFE-lined hotend won't be able to print filaments that require higher temperatures. PETG is at the upper end of what can be (safely) printed with a PTFE-lined hotend, while filaments such as polycarbonate require temperatures well outside the usable range.

  • A printer with a standard brass nozzle won't be able to print (not long, anyways) abrasive filaments such as glow-in-the-dark.

It is likely the printer at your lab will be able to handle TPU just fine. If it is a bowden printer then you might have some difficulty printing but it might still work depending on exactly how soft the filament is and how well-constrained the filament path.

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  • $\begingroup$ Some bullets are shortcuts, from experience I know that Bowden and 2.85 mm filament work just fine (although I acknowledge that 1.75 mm is more commonly used). PTFE lined heatbreaks can print ABS and PETG. Also not all direct 1.75 mm extruders can print TPU without tweaks/guides, the filament can buckle in the extruder, so a direct extruder isn't a given fact for successful printing of TPU. $\endgroup$ – 0scar Jun 7 at 22:08
  • $\begingroup$ Point 4 is just wrong. There is no reason to want an all-metal hotend for PETG. You only need that for exotic materials that require temperatures well over 250°C, which is the absolute hottest you'd reasonably want to go with PETG - it will be a dripping mess above that. Point 1 is kinda true, but it's just a matter of print speed. TPU is totally doable with a bowden and not even terribly hard. $\endgroup$ – R.. GitHub STOP HELPING ICE Jun 8 at 4:28
  • $\begingroup$ @R..GitHubSTOPHELPINGICE E3D lists the maximum temperature of their lite6 hotend as 245C. PTFE actually starts releasing toxic fumes at temperatures (much) lower than that.. I would consider printing PETG with a PTFE-lined hotend less than ideal. I have updated accordingly. $\endgroup$ – Tom van der Zanden Jun 8 at 6:51
  • $\begingroup$ @TomvanderZanden: Thanks for the link. This is the first I've seen of any citations on rigorous treatment of the subject at temperatures involved in 3D printing non-exotic materials. Some of the wording like "offgases particulate matter" is a bit dubious though and I suspect we'd need to read deeper into the sources to find out what it's really saying and whether there's any evidence of likely harm from the temperatures and amount of PTFE involved. $\endgroup$ – R.. GitHub STOP HELPING ICE Jun 8 at 17:20

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