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.
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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.
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.
Do you think the dryer or the nozzle helped more?
Dryer didn’t do squat to make a difference. The filament was at a steady 14Rh for several days for both nozzles. The only change that made a difference that made a difference was the nozzle swap.
No kidding! Thanks. I’m going to get a 6mm.
I seldom use a .40mm nozzle much anymore since I mostly do functional prints like these gears. I have found the .60mm nozzle is a good compromise for speed in printing, better strength, and good accuracy.
Interestingly enough, a .40mm will print nearly or as fast as a .60mm nozzle on Bambu printer in general. This because Bambu optimizes their slicer setting for the .40mm nozzle. What it does give up a bit is between layer strength. This is due to to the smaller contact area difference between layers. I can get the same strength with 2 perimeters using a .60mm that would take 3 perimeters with a .40mm nozzle.
Very interesting, thanks.
Filament drying is YouTube delusion.
Cue “hydroscopic, meaning plastic absorbs water”.
There are filaments that do need to be dried before use or even dried as you use them. But they are higher end engineering filaments and they cost real money. You tend to need a real reason to buy them. Despite the fact that many consumer level printers have the ability to print them these days. $50 to $100+ a kilogram or less, is a real barrier to the wide use.
Still, years of experience has taught me that I need dry PETG as it tells me it needs to be dried, and TPU is always dried before use. But PLA is a waste of watts.
Have you considered just using gear molds? Or getting some machined if they’re super custom and you’ll be making several of the same gear and replacing them over time.
I need to know if the gear train will fit on the banjo of the lathe first. I might run the plastic just to see how long PETG might last. If I want metal change gears, I will either spring for the 100+ dollars needed to buy the proper gears. Or I will spend $60 for the proper cutter and cut my own gears. But I need to be sure they will fit first.