- Joined
- Oct 29, 2012
- Messages
- 1,387
In short: I need a way to make a very smooth/polished hole about 1.85mm diameter and 2" long through the middle of M6x1.0 copper (preferably) or brass.
In long: I am needing to produce large parts with very soft flexible filaments (60-70 shore A) at a pace which suggests I get paid per part and not by hour, so "just slow down to 2mm/s" isn't a palatable solution. <conjecture warning - applies to the rest of this paragraph> I have come to the conclusion that a big part of the challenge is that on nearly every printer, the filament melt zone is not long enough. We are expecting plastic to go from room temperature to liquid state in the span of a 1/2" long hotend, and at low speed this works "well enough" but at higher speeds the plastic doesn't spend long enough in the melt zone. If you're using a rigid filament, you can get by even at higher speed just by brute force; just cram that filament down the gullet and it will come out one way or another, fully melted or not. But you just can't get away with this approach when the filament has the consistency of a gummy bear. I think this is why parts printed at high speed are weaker and this is why the shotgun answer to almost every 3D printing issue is typically "slow down" - even if people don't realize it when they say it, they're speaking to the inherent flaw in 3D printers. I have experience in industrial extrusion (wire, cable, tube) and never have I ever seen extrusion done this way - trying to rapid zap a cold polymer into fluid with only a second or two in the die. There is always a long heated barrel that the plastic must travel through before reaching the die, to ensure it is fully melted when it gets there. This barrel, and the die, and the screw, and every other mechanical element in contact with the molten plastic is ground to a very smooth finish.
So I have concluded that I need a long melt zone with a bore that has a very smooth/polished finish.
This is what I have currently:
My heater on the left, stock heater on the right. I have a melt zone 5X longer and with 6X more heating watts than stock.
I am using the OmniaDrop extruder which is renown for its ability to handle flexible filaments.
I have made the barrel out of Amazon knockoff "Volcano" nozzles for which I parted off the tips on the lathe so they are now just threaded M6 brass tubes with about 1.85mm ID. This works but leaves interruptions in the bore that I think generate turbulence. It should be one long piece I think. I tried drilling out the center of the makeshift barrel to a slightly larger size and this actually hurt performance. I am not positive but I think the issue wasn't the new larger size, but rather the lower quality surface finish left by the drill bit. So I have convinced myself that the bore of the barrel and the bore of the nozzle need to be extremely smooth. Some higher end nozzles do come with a smoothness spec and I will use them, but the nozzle itself is not the issue I am concerned with at the moment - it's the bore I'm focused on.
I am going to try the "supervolcano" nozzle as a combined barrel and nozzle.
but this isn't really convenient because it will require complete disassembly of the hotend to change the nozzle, I could cut the tip off like I did for the volcano nozzles but still I am not convinced the bore will be "perfectly" smooth. So how could it (or a home made barrel) be made smooth inside when it's such a small ID? I have looked and not found any kind of hone that small. Chuck up a toothpick in the drill and cover it in lapping compound?
In long: I am needing to produce large parts with very soft flexible filaments (60-70 shore A) at a pace which suggests I get paid per part and not by hour, so "just slow down to 2mm/s" isn't a palatable solution. <conjecture warning - applies to the rest of this paragraph> I have come to the conclusion that a big part of the challenge is that on nearly every printer, the filament melt zone is not long enough. We are expecting plastic to go from room temperature to liquid state in the span of a 1/2" long hotend, and at low speed this works "well enough" but at higher speeds the plastic doesn't spend long enough in the melt zone. If you're using a rigid filament, you can get by even at higher speed just by brute force; just cram that filament down the gullet and it will come out one way or another, fully melted or not. But you just can't get away with this approach when the filament has the consistency of a gummy bear. I think this is why parts printed at high speed are weaker and this is why the shotgun answer to almost every 3D printing issue is typically "slow down" - even if people don't realize it when they say it, they're speaking to the inherent flaw in 3D printers. I have experience in industrial extrusion (wire, cable, tube) and never have I ever seen extrusion done this way - trying to rapid zap a cold polymer into fluid with only a second or two in the die. There is always a long heated barrel that the plastic must travel through before reaching the die, to ensure it is fully melted when it gets there. This barrel, and the die, and the screw, and every other mechanical element in contact with the molten plastic is ground to a very smooth finish.
So I have concluded that I need a long melt zone with a bore that has a very smooth/polished finish.
This is what I have currently:
My heater on the left, stock heater on the right. I have a melt zone 5X longer and with 6X more heating watts than stock.
I am using the OmniaDrop extruder which is renown for its ability to handle flexible filaments.
I have made the barrel out of Amazon knockoff "Volcano" nozzles for which I parted off the tips on the lathe so they are now just threaded M6 brass tubes with about 1.85mm ID. This works but leaves interruptions in the bore that I think generate turbulence. It should be one long piece I think. I tried drilling out the center of the makeshift barrel to a slightly larger size and this actually hurt performance. I am not positive but I think the issue wasn't the new larger size, but rather the lower quality surface finish left by the drill bit. So I have convinced myself that the bore of the barrel and the bore of the nozzle need to be extremely smooth. Some higher end nozzles do come with a smoothness spec and I will use them, but the nozzle itself is not the issue I am concerned with at the moment - it's the bore I'm focused on.
I am going to try the "supervolcano" nozzle as a combined barrel and nozzle.
but this isn't really convenient because it will require complete disassembly of the hotend to change the nozzle, I could cut the tip off like I did for the volcano nozzles but still I am not convinced the bore will be "perfectly" smooth. So how could it (or a home made barrel) be made smooth inside when it's such a small ID? I have looked and not found any kind of hone that small. Chuck up a toothpick in the drill and cover it in lapping compound?
