I'm printing some change gears to check the fitment of the gear train on a banjo. I have been fighting with this particular brand of PETG trying to get a clean and accurate print since last week.
Notice on the 2 20T gears the poor bores and under extruded 5 layer top surface. They were printed with a hardened .40mm nozzle on a Bambu A1 Mini. They do NOT fit the spindles on the banjo at all.
Now look at the larger 80T gear. Clean teeth and bore with proper flow rate on the top surface. (Yes the infill is showing a bit due to the mere 3 top and bottom layers I printed it with to save on filament). This gear fits as it should right off the plate.
Same exact filament, same printer, same exact slicer setting. Just a hardened .60mm nozzle swapped for the hardened .40mm nozzle. And dried to 14%Rh for days and I printed directly for the dryer.
Soooo much time and filament wasted calibrating and recalibrating for that .40mm nozzle and it still failed. All I needed was the .60mm nozzle. But, still a new and interesting phenomenon to learn from for me.
Just a question, but why is the large gear solid like that? It's probably printed at some low infill, so it shouldn't matter much. But I think you can massively reduce printing time and material needed, while at the same time increasing the strength of the gear, if you were to switch to a spoked design.
You know... I just had to test it.
Just threw together a model with some holes, it's actually faster to print without the holes, even though it uses slightly less material, because there's fewer retractions and nozzle hopping around.
I'm sure you can optimize it more, but for a quick test, just throwing a solid disc out there will most likely be faster to print.
edit: accidentally had the gear teeth bigger on the non-hole version - they're the same now.
Thanks for trying it out. I would model something up, but don't have time right now. It would also depend on the slicer used, the printer and the settings etc.
It probably doesn't matter that much and not be worth the effort unless it's really what you want. But for a quick prototype just having it solid is fine and not worth optimizing.
I've tried adding holes in some things and sometimes it uses more filament since the walls often use a lot more filament than sparse infill, even with the holes.
Part lazy design choice and part running these gears for a few minutes at speed to observe real world function. Spoked FDM plastic gears probably would not run long enough at 500rpms and there is no soft start on a lathe. And since most of the strength with FDM printed items lies in the skin of the part, removing half the skin would reduce the rigidity.