Question about surface finish
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I have run into an interesting situation in regard to surface finish. The prints you see are done in PETG at 230C nozzle temperature.
The bottom print one was done with filament that has probably been sitting on a stand in the open for a year. Relative humidity is hovering in the 40-50%. There was no steam or popping but the 'spitting' action of the nozzle was quite evident on the first layer. The finish is actually quite attractive if you are into a somewhat sandy texture finish. It does hide a lot of sins as well.
The middle print was done after drying the filament for 8 hrs at 75C. There was no spitting at all and the finish is nice and shiny like what I would expect this filament to produce.
The third print was done about 18 hours later with the same filament that was previously dried. The surface finish is not as rough as print #1 but it shows definite signs of heading that way.
I have never had issues with moist filament before (PETG or PLA) and I only dried it because of the very clear spitting action of the first line put down on the bottom layer - it was not continuous (and this is after the skirt was printed).
I would be interested to hear what people think - is it possible for PETG to absorb so much moisture in such a short time as to effect the print this much? It is older filament, possibly 3 years old in total but only out in the open for a year and relative humidity in the print location is low.!
Print speed was 50 mm/sec but it is a large printer (Creality CR 10 S5) with a bit of mass to it and the ringing is not unusual.
petg surface finish.jpg -
@jens55 I have printed a lot of PETG and never noticed hissing even if the filament is left out on the machine for a few days between prints. I have noticed that I can modulate the finish of the prints by printing hot and changing the print speed. I have printed some parts with horizontal stripes of alternating crystal clear and frosty finishes that look pretty nice. IRIC, I printed at 155 or 160C and got frosty with speeds around 20 mm/sec and clear with speeds around 50 mm/sec using a 1mm nozzle and volcano heater block. I don't seem to have any photos of the parts, but I'll dig around and see if there are some on my camera's memory card.
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I dont know your method of drying but I suspect that when you dried the filament, only the outer, exposed portion of filament dried thoroughly. The middle print of the pic used the outer portion that was more dried hence the better surface texture, and the third print used the inner portion of the spool which was which was not as dried.
Im guessing that its not so much moisture absorbed so quickly, but rather the entire spool was never dried entirely.
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@wwak84, I was thinking of that possibility and actually that is the only thing that makes sense. The bit that doesn't make sense and that I failed to mention, is that there was no transition from shiny to matte finish. The third print was, as I mentioned, not as rough a finish as the first one but there was zero evidence of matte finish at the end of print #2 and zero evidence of clear finish on print #3. Of course it is possible that this was a stroke of luck but it is odd. It could also be that if there was moisture left in the inner layers of the spool, that it had time to migrate towards the outside layers while it was sitting between print 2 and 3.
The print is 80g according to Cura and there is less than 80g left on the spool after the third print. The print takes around 6 hrs to complete. Drying was done in a high end home food dryer that uses a thermostat for heat control (I also have a dryer that has different power settings and does not verify the temperature). The fact that there was only around maybe a third of the spool left and that I ran the dryer for 8 hrs, makes it difficult for me to believe that it wasn't dried thoroughly .... but of course that is a good possibility.
Thank you for your thoughts! -
@mrehorstdmd, I am surprised that you were able to print PETG at 160C. My PETG spool recommends 220-250C for print temperature and I doubt that I could go below 210 even if I slowed the printer to a crawl. I think that your filament composition must be substantially different than mine. I suspect you get a frosty finish at that low a temperature because the filament is just barely liquid.
Nevertheless, it is interesting to hear that surface finish can be influenced by temperature and/or print speed.
In my case neither speed not temperature was changed during the prints. Now that I think about it though, print #2 had a bit of sagging in a couple of corners and in print 3 I had turned on the cooling fan to 30% (it might have reduced the sagging a bit but not much). Normally I print PETG with no print cooling fan.
Thank you for your thoughts! -
@jens55 yeah, 260C, not 160... hadn't had my coffee...
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@mrehorstdmd said in Question about surface finish:
@jens55 yeah, 260C, not 160... hadn't had my coffee...
Hmmm, that puts a different spin on the situation. I have not tried printing that hot but I should try printing a bit hotter just to see what happens. Thanks! -
@jens55 I would suggest a dry box (air tight box with silica gel bead desiccant) for filament storage. I found a plastic tote at a hardware store that had a rubber gasket seal and latches on all sides. Ordered color indicating gel bead desiccant from Amazon (changes color depending on how much moisture is absorbed). The desiccant can be dried in the oven at ~200*F, microwave, or other means.
I wouldn't spend too much time contemplating this since it was such an old spool. If the issues persist on new filament, definitely get a dry box for long term storage if you can, and also look into a filament dryer like on of these. I have a similar one and it works great.
edit: also I put the silica gel beads into a mesh bag so they weren't loose in the tote, something like this
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@wwak84, thanks. The spool is just about done so I am not too worried. I just wanted to understand what was happening and why. Also, I actually like the rougher finish as it hides layer lines.
I have been into 3D printing for a few years now and this is the first instance where drying made any substantial difference. I think there were other occasions where drying reduced stringing a bit but it was never a drastic difference as in this case.
I will see what a fresh roll of filament will get me.
