Any issues with PETG?


I’m looking to build my first OFM and recently got a lovely 2kg spool of very dark (almost black) recycled PETG prusament. I’d print with PLA as per the instructions but:

  1. really want to use recycled filament and Prusa are currently out of stock, and
  2. imagine that I won’t be so fortunate in getting an almost black spool of recycled PLA,
  3. have had bad experiences with other brands of recycled filament

I notice on scouring the forums that @WilliamW, nethead, @AmateurEngineer & Lost have all mentioned using PETG. Can I ask if you regretted it in any way?

If so, I’ll wait for Prusa to get more rPLA in stock and get 2kg of that and a 1kg spool of black. Or indeed… does anyone know of a more matte and/or black (or otherwise suitable for OFM optical bits) than Prusament PLA Jet Black?

Sorry @nethead & @Lost - that was my first post, so discourse wouldn’t let me mention more than 2 people…

I have not really used my PETG microscopes in anger yet. They are destined for a colleague to test in an incubator but I have not got them fully set up. However there are no issues with PETG that I have seen from just playing with them a bit so far.

I am using RS PRO PETG filaments (same for PLA), they are easy for us to get and seem to be reliable. Not recycled though :frowning:

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Thanks for the rapid reply @WilliamW, that’s good to know. Is it the RS PRO 1.75mm Matte Black PLA Matt 3D Printer Filament that you use for the black bits? They do seem to have a RS PRO 1.75mm Black Recycled PLA 3D Printer Filament in stock, it’s just not matt, but probably better than the Prusa black option, that I mentioned, which is neither matt nor recycled…

I just use black, not Matt. There are internal light trap structures where th reflection needs to be low. The ordinary black prints pretty Matt for the first print, I think until it gets a bit wet…

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Might be interesting to consider using black felt in the imaging system instead of or in addition to the printed light trap.

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Brilliant, I found a 1kg spool of recycled black that I’ll put on backorder for my black bits at least. Sorry to anyone reading this in the future looking for a definitive answer on PETG…

@tkircher I was thinking of roughing up the interior with sandpaper, I presume that would help too. I guess it would be good to see if there’s an actual issue that needs solving though. Have you had problems low contrast?

No, never had any issues with contrast. Also printed an optics assembly without the baffles, and also printed one in white PLA, and didn’t see any difference. So I wouldn’t worry about it too much. I do think it’s worth considering alternate materials and designs, just to get people thinking.



i did do a testprint of the z-actuator as recommended by WilliamW using (ESUN) PETG which worked out fine. When printing the main body the print stopped due to a blob buildup which is a problem of my hotend / nozzle setup (no silicone sock yet). After this i did switch to PRUSA PETG which i had in stock for a “special print”, which openfelxure certainly is. Some parts like the wheels/gears and the LED array holder i did print in ABS.

With my limited experience i would say its feasible to print all parts in PETG. Nearly all parts, except fine threads, are also printable using a 0.6mm nozzle and 0.3mm layer height. Which saves around 25% to 30% print time compared to the standard, 0.4mm nozzle.




I think the printed one is plenty good enough for normal use, where stray light is not a massive problem - but once you add the beamsplitter module for fluorescence, some sort of proper light trap (e.g black felt) is very helpful. Reworking the instructions for fluorescence to make it a bit more prominent is on the long-term to-do list…

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I have previously used relatively thick layers (0.24 I think, as it was a default on my Ormerod) and observed, as you do, that it doesn’t hurt. It’s worth knowing there are a few places where layer height >0.3mm may cause issues, particularly in the thin horizontal bridges where I think I’ve assumed a layer height below 0.25mm (I think it’s important that the flexures have at least two layers for reliability of printing, so there are a few structures 0.5mm thick). That’s not to say 0.3mm won’t work - it mostly should - but it’s possible to get unlucky depending on where exactly the layer boundaries fall.

I’ve not played much with the 0.6mm nozzle, but the design’s been optimised to avoid relying on thin structures in X and Y, which should help there. There are a few structures that are quite thin (like the walls) so it would be interesting to see the G code visualised for that - I am curious whether you end up with fewer perimeters or voids where there should be solid material.


should i send you the gcode? (Prusaslicer with MK3S config)

can do - or possibly what’s most convenient is just to take a screenshot or two of layers in prusaslicer, showing the “wall” around the actuators (say ~10mm from the bottom). I’d be curious to see how it slices. I’d also be interested to hear how many layers thick the flexures are - again, easiest to use single layer view in Slicer to scroll through them.