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From PLA to Clear PETG

SusanOKC
(@susanokc)
Famed Member

Hi, 

We've been printing exclusively PLA on our Prusa. We have two parts it would be ideal to print with clear filament.  After doing some research, we bought a roll of clear Overture PETG. Not having used PETG before, any tips before we get started? I'm attaching our first pass at a test slice.  

Thanks!

 

Quote
Topic starter Posted : 13/05/2021 10:02 pm
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi Susan,

Nice to hear from you again 🙂

To print PETG, you can use your optimized PLA profile as a starting point and make these modifications:

  • Increase nozzle temperature (I use 210°C for PLA and 220°C for PETG)
  • Increase bed temperature (I use 50-60°C for PLA and 70-75°C for PETG). This is the most critical step because PETG will detach right off the bed if the temperature is too low.
  • Reduce your highest speeds to about 80% of what they were with PLA. So not more than 50mm/s for walls (inner perimeters), 25-30mm/s for outer perimeters and 60mm/s for infill. PETG doesn't melt as fast as PLA so this will help avoid extruder clicking. In your case your speeds are already fine except for perhaps the infill and solid infill speeds. Your extruder will probably struggle to handle 80mm/s on high layer heights with big extrusion widths - if you experience clicking, you may need to take that down to 70 or 60mm/s (more about the necessity for high layer heights later). 
  • Lower your first layer speed if necessary. I suggest 15-20mm/s in PrusaSlicer or 30% in Simplify3D. This helps with the critical first layer adhesion. You will probably be fine with your existing 20mm/s.
  • Lower first layer acceleration to 400mm/s²
  • In the cooling tab, you can reduce the minimum feature time ("slow down if layer print time is below...") to 5 seconds as PETG is much more resistant to overheating. This slightly compensates for the slowdowns you'll get from all the other tweaks by making small layers print up to 3x faster than before. If pointy features like the tips of pyramids or the chimney of the benchy come out wispy and deformed, increase this to 7-10 seconds, but my printers have no problem going down to 5 seconds
  • Increase max cooling fan speed to 100%
  • Make sure the nozzle is absolutely completely free of PLA. Any residual PLA will make the PETG layers not bond together. The print will look fine but the first 20 layers of your calibration cube will fall apart in your hands (basically the first couple of layers until the PLA contamination was purged out by the print itself).

 

For transparent PETG, some additional strategies will make the print more transparent (although you'll always get non-transparency at each layer line due to the air pockets, so at best your print will look like a frosted lightbulb effect rather than clear glass or transparent water bottles):

  • Use the highest temperature possible. 230-235°C on PTFE-lined hotends, 250°C or more on all-metal hotends.
  • Use the thickest extrusion width and highest layer height possible (with a 0.4mm nozzle that's 0.48-0.5mm extrusion width and 0.3mm layer height). This makes for a coarser, uglier print but yields less layer lines and hence less areas where transparency is affected
  • Slow the print speed down even further than the above (but keep an eye on print time and see how much slowdown you can tolerate - slower speed doesn't contribute that much to improved transparency)
  • Turn on ironing every layer ("all solid surfaces"). This should permit you to make optically clear transparent prints (like lenses). Unfortunately it is still broken in PrusaSlicer 2.3.1 and it only irons the topmost layer rather than all of them. But I'm placing this here in preparation for when (if?) it eventually gets fixed 😆 . Beware that this drastically increases print time.
  • Remember that infill will now be visible, so use a nice pattern (or zero infill) and make sure to turn off the "only retract when crossing perimeters" option so you don't get ugly strings within the infill where travel moves are (this is something that we never have to worry about with opaque filaments 😉 - your setting is already correct here)

You do have the option of using the canned profile for PETG that comes bundled with PrusaSlicer as you posted in the attached gcode, but since you've already spent many months fine-tuning this PLA-based profile I've given you enough info above to give you the option of making the above modifications to the PLA profile so you can retain those tweaks if desired, rather than starting from scratch with a new PETG profile.

Hope this helps, let me know how it goes! 🙂

Regards,
Luke

ReplyQuote
Posted : 13/05/2021 11:23 pm
Pablo liked
SusanOKC
(@susanokc)
Famed Member

Thanks, as always! Do you know of any options to print something transparent on the Prusa? This is a piece that sits on top of 60 knitting needles blocking them from view.  It would be helpful if the top piece could be transparent so one could see if the stitches were knitting well or if there was an issue before continuing.  Any ideas?

Thanks again! 

P.S. All of your great tips and guidance have been so helpful! We launched the company 2 months ago and can't even believe the success we're having. In the first 6 weeks we'd surpassed the number of sales we'd hoped to have in the first year. We would need 20 printers to keep up with the number of orders we're getting per day. Crazy. I will be back soon to talk about additional strategies to speed up our prints. We just got .6 and .8 nozzles at your suggestion but haven't yet played around with them. We really appreciate you, Luke, and are so grateful for this service and your wonderful support! 

ReplyQuote
Topic starter Posted : 14/05/2021 5:27 am
Luke
 Luke
(@lmf5000)
Expert Moderator

@susanokc Hi Susan,

You're welcome :). Glad to see that we're facilitating you business and you're experiencing such strong growth. It's always very rewarding to hear such nice feedback from our users 🙂

To print something transparent, there's two approaches -

Option 1:

If you're going to 3D print it, make the transparent part have as few layers as possible (2 or 3). The bottom layer will be transparent because the build plate keeps the plastic level and removes the air gaps between the diagonal lines (air gaps are the main source of opacity in 3D printed "transparent" parts). The topmost layer will be transparent because the ironing pass fills out the gaps. Every middle layer in-between will be full of diagonal lines with air gaps between the lines which will refract light and make it hard to see through. With one middle layer (so 3 layers total) you'll be able to make out the needles if they're not too far from the printed window. With two middle layers (4 total) it will be twice as hard to see through. If you use the full complement of 3 bottom + 3 top layers, there's a good chance it will be too blurry to make out individual needles. This has been my experience, however I run PTFE-lined hotends (since they're much more resilient to blockages with low-melting plastic like PLA which is crucial when printing with a tiny 0.2mm nozzle as the feed rate is low and pressure is high so blockages become very likely).

You have an all-metal hotend so you can leverage its greater temperature capability to increase temp to 250°C or beyond, which makes the filament more transparent. With a bigger nozzle (0.6-0.8mm) you will have wider extrusion widths, which means less air gaps between consecutive lines of solid infill and hence less diffusion/blurring areas for a print of the same size (in essence going from 0.4mm to 0.6mm means 50% less air-gaps). And with a bigger extrusion width you can go for higher layers, which reduces the layer count necessary to achieve the required thickness/strength.

Option 2:

Simply design a cutout and retaining mechanism in your print, and affix a transparent window in that part. The transparent window could be made of thin perspex or acrylic which you yourselves cut with a saw or blade or water-jet or laser machine, or you can order the pre-cut to size from a supplier, or you can use thin plastic (water-bottle gauge) and cut with scissors or tin-snips. You attach to the print using glue or design a 3d-printed fastening mechanism (friction or snap fit) or use a design with self-tapping screws. If you go for glue make sure it can withstand heavy use (I learnt from experience that hot glue for example is very weak and the prints will quickly fall apart). If you go for friction or snap-fit use PETG because PLA will slowly deform over time (the engineering term is "creep", where a material ends up with a permanent deformation as a result of continued force well below its breaking force) and loses its grip, so the window could fall out a few months after production.

This second option gives you more flexibility in terms of colour and material choice, and a better overall result in terms of clarity - but adds an extra item to keep in stock with all the associated problems (lead time, supply chain management etc.).

Hope this helps! 🙂

Regards,
Luke

ReplyQuote
Posted : 14/05/2021 11:43 am
Pablo liked
SusanOKC
(@susanokc)
Famed Member

Hi, 

Those are helpful thoughts, and probably mean the clear filament idea won't work out. The piece is highly structural and functional. It's the top circular piece in the attached photos. Knitting needles need to ride in the piece to actually help do the knitting. And its much thicker than just a few layers - more like 10mm.  It would be great to see through it, but if it's going to be so cloudy to see through, there's no reason to go down that path. So that at least saves me some time trying to become a PETG expert, LOL.  Thanks again!

 

IMG 1306
IMG 0474
ReplyQuote
Topic starter Posted : 14/05/2021 8:52 pm
Luke
 Luke
(@lmf5000)
Expert Moderator

Hi Susan,

You're right, the design for that is very much the opposite of what you need to make a good transparent print 😆 . Every single angle has several millimetres of thickness. I don't know if it's advisable to print this out of plastic at all actually. This looks more like an embroidery machine than the simple sewing machines I'm used to working on, but your two main concerns will be dimensional tolerances for an accurate thread path, and wear and tear from the passage of the thread and needles. Metal can handle it no problem, but PETG isn't a very hard plastic (quick primer in engineering terms: hardness is a measure of the resistance of the surface to scratching; stiffness is a measure of the force required to bend it, and toughness is a measure of how much impact it can absorb. PETG is less hard, less stiff, but more tough than PLA. In other words, if PLA was glass then PETG would be rubber. I'm exaggerating for the sake of simplicity - in actual fact PETG feels like regular plastic, just springier than PLA and almost impossible to shatter).

This is all theoretical though. Since it's only 30-50g of printing, if I were you I'd just print one and see how it goes. You might be able to see enough transparency to still achieve your aim of checking if the needle is in the right place. You don't need perfect optical clarity for that. You might also use that prototype to refine it to include thin clear windows (or even holes) in certain key parts, strategically placed so that they don't compromise the strength or function of the part but allow you to view the critical stopping points of the mechanism with clarity.

---

3D prints require a completely different thought process than normal parts because they are hollow, so they actually work a lot different to solid plastic. In solid plastic, holes reduce strength - but in 3D prints the holes are much stronger than the rest of the print, because they're made of perimeters rather than infill. And with solid plastic, thickness adds strength proportionately (2x the thickness = 2x the strength). With 3D prints, thicker/bulkier parts aren't significantly stronger than thinner parts, because you're just adding hollow infill in the middle. Whether a part is 2mm or 20mm, you effectively still have 4 perimeters making it up (1.6mm of plastic). You will gain some strength due to the top and bottom layers, and due to the wall being further from the center (when something is loaded in bending, the further from the center your material is the stronger the beam; that's why I-beams concentrate their material on the horizontal top and bottom of the "I" with just a relatively thin vertical line in the middle to keep the top and bottom spaced out - it can withstand much more bending force than the equivalent weight of metal in a solid cylinder or bar for instance). So you can actually make rather drastic dimensional changes without seeing a proportionate difference in strength. Of course in your case dimensional considerations (correct thread and needle path) will determine the wall size and you don't really have much room to change it.

---

Anyway, hope this helped some more. If I were you I'd try one and see. If the top side isn't too highly loaded in terms of strength, you can print it without infill (above 6.6mm or so) for more optical clarity. Obviously take precautions so you don't damage an expensive knitting machine if the printed plastic parts fail. I'd run it with hand power instead of motor power for the first couple of cycles if that's an option, it will limit the energy and power flowing through the machine 😉 .

Regards,
Luke

ReplyQuote
Posted : 16/05/2021 1:13 am
Pablo liked
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