MK4 settings and hardware modifications for 90A TPU?  

Print very slowly - the softer the flex the slower the print or the extruder's interior pressures will be awry.

And yes, I suspect that the minimal grip/idler pressure will be necessary but the Mk4 may not be as sensitive in this.

Cheerio,

RE: MK4 settings and hardware modifications for 90A TPU?

here's a link to the polymer site profiles downloads - no Prusa but they do have cura

https://polymaker.com/download-material/

RE: MK4 settings and hardware modifications for 90A TPU?

Thanks, PeterT - unfortunately, there's no profile (for any printer) for 90A. They have one for 95A, but it probably isn't suitable for 90A, which is significantly softer.

Initial results (success!):

Based on the Polymaker PolyFlex TPU90 web page and the Polymaker TPU90 product documents, I created a custom filament profile in PrusaSlicer for Polymaker TPU 90A. This profile is based on a standard flex filament profile ("Generic FLEX," I think), with the bolded settings changed from the generic FLEX profile:

Filament:

• Diameter: 1.75mm
• Extrusion Multiplier: 1.3 (as per the Product Information Sheet (PIS), page 4: "It is recommended to slightly increase the extrusion multiplier (+0.2) to ensure a more consistent extrusion.")
• Density: 1.12 g/cm3 (as per the Technical Data Sheet (TDS), page 2: "Density: 1.12 g/cm3")
• Cost: $53/kg (as per MSRP of USD$40/750g)
• Spool weight: 750 g
• Temperature, idle: 70C
• Nozzle: First layer - 230C; other layers - 225C
• Bed: First layer - 50C; other layers - 50C

Filament Overrides:

• Retraction Length: 3.0 mm (as per the Technical Data Sheet (TDS), page 3: "Retraction distance: 3 (mm)")
• Retraction Lift Z: 0 mm
• Retraction Speed: 40 mm/s (as per the Technical Data Sheet (TDS), page 3: "Retraction speed: 40 (mm/s)")
• Deretraction Speed: 20 mm/s
• Minimum Distance After Retraction: 2 mm
• Wipe While Retracing: Unchecked

The Technical Data Sheet (TDS) also lists (at page 3): "Printing speed: 30-60 (mm/s)" - this is consistent with the general recommendation to print TPU slowly. Unfortunately, nothing in the filament profile corresponds to this setting, which is disappointing. The closest setting, as best I can tell, is the section of Printer Settings reading: "Maximum Feedrates," with individual settings for X (default 200mm/s), Y (default 200mm/s), Z (default 40mm/s), and E (default 100mm/s). I changed the X, Y, and E settings to 50 mm/s and left Z at its default.

I loaded the filament into the MK4 using the "FLEX" profile. The extruder grabbed the filament and started drawing it in, but no filament came through the nozzle. It took 5-6 "Purge More" cycles to get a purge length of filament through the nozzle - which was a little concerning - but after that, it was OK. I noted that the purged filament seemed softer, less viscous, and a little more more drippy than standard PLA/PETG/etc., but I presumed that this was consistent with its soft properties.  

Using the above settings, I loaded a test model (ring: 30mm x 30mm x 10mm cylindrical shell with 20mm x 20mm x 10mm cylindrical hole) and started printing. My printer immediately did something very weird - during startup, it started an axis check, but the print head reached the end of the axis and then kept grinding against the end, trying to go further. This lasted for about 15 seconds, during which the printer UI was unresponsive, and the printer did not detect the error and trigger a timeout.

I shut off the printer, waited a few moments, and turned it back on - and it immediately resumed the axis grinding. This recurred several times, and only stopped when I hit the Soft Reset button on the printer. I presume that the "power loss resume" features of the printer were at issue here, but it is concerning that the printer kept retrying this behavior and didn't have a timeout mechanism. Clearly, it needs one to prevent damage to the motors!

Once I managed to stop this behavior, I ran a full recalibration process, which includes an axis check. The MK4 passed without incident.

I presumed that the problem was my modification of the "Maximum Feedrate" settings, so I reverted those settings (leaving only the modifications to the Filament Settings profile), resliced the model, uploaded the new model, and printed it.

The test print worked fine with these filament settings. The finished print was exactly as expected and didn't have any issues.

I noted that the print was very difficult to remove from the smooth PEI sheet. The model was so tightly bound to the sheet that trying to remove it manually was completely ineffective. I was able to scrape it off using very careful application of a painter's trowel, but it was surprisingly difficult, even given its relatively small cross-section. The sheet doesn't look damaged, but it might have been, especially for larger models. In the future, I will use a power-coated textured sheet, which I believe to be a common recommendation for TPU.

Lastly, I had no issues unloading and purging the filament. I swapped it out with a standard PLA spool and found no unexpected TPU residue during the purge, and no indication of a nozzle clog.

Overall, this initial attempt was a success. I did not experience any problems with extruder jams, TPU residue, or print defects. More complicated models will probably require additional tweaking.

I remain puzzled about the unavailability of "print speed" settings in PrusaSlicer. Unless anyone here has any advice of where to find this setting, I plan to submit a feature request on the GitHub repository for PrusaSlicer to add this setting to the filament profile.

Use a layer of glue(stick) to reduce adhesion with TPU.

Create a Print Setting to go with the Filament Setting - put the speeds in there.

Cheerio,

RE: MK4 settings and hardware modifications for 90A TPU?

I’ve run into the axis grinding routine at the start as well. I found the drag of the filament was enough to screw up the start. I now do an auto home when I change filaments at the start of a print and make sure there is slack in the filament. 

RE:

Posted by: @david-s174-2

 

Using the above settings, I loaded a test model (ring: 30mm x 30mm x 10mm cylindrical shell with 20mm x 20mm x 10mm cylindrical hole) and started printing. My printer immediately did something very weird - during startup, it started an axis check, but the print head reached the end of the axis and then kept grinding against the end, trying to go further. This lasted for about 15 seconds, during which the printer UI was unresponsive, and the printer did not detect the error and trigger a timeout.

I shut off the printer, waited a few moments, and turned it back on - and it immediately resumed the axis grinding. This recurred several times, and only stopped when I hit the Soft Reset button on the printer. I presume that the "power loss resume" features of the printer were at issue here, but it is concerning that the printer kept retrying this behavior and didn't have a timeout mechanism. Clearly, it needs one to prevent damage to the motors!

Once I managed to stop this behavior, I ran a full recalibration process, which includes an axis check. The MK4 passed without incident.

I have been unable to overcome the X-axis failure. I got a print to start a couple of times but the settings weren't right and the extruder jammed. I slowed the speed but now I am stuck at this point.  Did you have to reslice the model or reload it?

Thanks