PETG print has hourglass shaped edges
Hello,
I am attempting to print a gear for an antque car speedometer pinion. The gear will be exposed to sunlight and needs to take a small amount of load. I selected PETG for this application. This was my first time using PETG and the print was not very good.
Filament Used : Prusament brand PETG
Filament settings : Default for Prusament PETG in Prusa Slicer
Machine was in enclosure with ambient controlled to 35C
Machine: Prusa MK3S+
Print settings in Prusaslicer were default for 0.05mm Ultradetail except:
100% infill
10 Perimeters
The gear teath are C shaped, thicker on the first and last few layers, but necked down in the middle.
Gear overview
RE: PETG print has hourglass shaped edges
This is what the gear should look like:
Print settings in Prusaslicer were default for 0.05mm Ultradetail except:
100% infill
100% infill is almost always a mistake, try cubic infill at about 25% as I suspect thermal contraction is distorting your print. There is nothing here that needs 0.05mm layers, 0.2mm should be OK.
10 Perimeters
This might be excessive, I would generally expect 6 to be enough. For gearing, elephants foot compensation helps to prevent jamming and if your involute tolerances are tight it may be worth printing exterior perimeters first - in Layers and perimeters on expert setting.
Cheerio,
RE: PETG print has hourglass shaped edges
I print lots of stuff with like 10 perimeters and 90% rectilinear infill from PETG without issue.
Another thing to check is look at the perimeter of the part in PS and switch between classic and arcahine perimeter generation. I have had some gears turn out weird with arachine. After printing the parts I could see the error in sliced preview, when I switched to classic the preview was fixed and the parts turned out fine.
I almost exclusively use arachine, but in that particular case classic was better.
RE: PETG print has hourglass shaped edges
Thanks for the tips. I will print again with 0.15mm layers, & 50% infill. I think keeping the perimeters is helpful as it will ensure the teeth are solid. (this is a real part used on an antique car speedometer and it needs some strength)
Do you suggest turning off the enclosure ambient heating? I had it set at 35C and maybe that prevented the layers from solidifying quick enough exacerbating the shrinkage?
Thanks!
-Joe
RE: PETG print has hourglass shaped edges
35 Should be ok in my experience.
I'm not sure reducing the layer height will do anything.
RE: PETG print has hourglass shaped edges
I'm not saying that this is causing your defects in this particular case but I've learned the hard way not to close the enclosure doors when printing PLA or PETG. I do so when printing ASA or PCCF.
Also, I'm with Diem, I'd print this with 4 to 5 perimeters and 25% cubic or gyroid infill. And with 0.3mm layer height as there's zero vertical detail to worry about.
Formerly known on this forum as @fuchsr -- until all hell broke loose with the forum software...
RE:
Follow up -
Linkade a second gear. This one is used 45% infill, 0.15mm layer thickness, and I did not turn the enclosure ambient heater on and left the door open. I changed the top layer width to 0.3mm to make the top layer smoother and that worked, but there were small gaps on the top face near the root of the gear teeth. I also changed PETG, but that was to better match the color of the original fiber gear. It seemed to work fine and is installed on the car.
Thanks for the help and tips!
