Hello everyone. I am hoping that someone here will be willing to share the secret ideal setting for a bowden direct drive extruder. I personally have been unable to get this style of extruder to work reliably. I did extensive testing and found that because you have a hose with a larger diameter then the filament you can end up with as much as 75mm or as little as 25mm when you tell the machine to extrude 50mm. This is because of the extra space in the hose, but you need to have some extra space in order to push the filament through the hose. Too tight a hose will have too much friction. I did more research and found someone who did the math and made an equation to calculate a number of steps per mm. I also found that because you use a hobbed gear that bites into the material it is prone to striping out the plastic so bad that it can no longer grab more to push through. This happens when your hot head jams or your hose causes too much friction. This is why I am asking for someone to share the “secret” to bowden style direct drive extruders. I notice all most every deltabot uses these and just wonder if anyone else has this much trouble getting them to work. Thanks in advanced to anyone who is willing to help.
Well, after the slack in the tube is used, it is used. It will not affect your feed rate. It will affect your minimum retract if you use retract. It will also affect your initial feed. You should make sure to prime the nozzle and remove the string shortly before printing.
I do not see any reason why you could not lube the hose once in a while. I have not lubed the hose in my bowden style delta printer, but I don’t see why you couldn’t.
You might want to occasionally preheat your oven and then sit the spool of filament in it on warm for an hour. I am not an expert on that, but it seems the humidity being absorbed by the filament will cause the filament to require a higher temperature to work without clogging the nozzle and the plastic will be expanded more than it should be when it squirts out of the nozzle.
Thanks for the response. Yes, you are correct about the slack and retraction. These were other issues I also ran into. You tell it to retract but because of the slop in the hose it doesn’t really work. Retraction is supposed to relieve the pressure and stop extruding but still let you start again fast. But again because of the slop in the hose you don’t get accurate retraction. Also I do prime my hot head prior to each print. I also have it print a few test bands to be sure it is working. I may have to try the oven thing, I have heard of doing that but not tried it.
Ive tried Bowden tubes a few times and don’t care much for their difficulties. In the end resistance in the tube with the tradeoff of backlash in a bigger tube isn’t worth the problems. On the printer I did last week I tired a Bowden tube and finally last night I printed a modified printhead holder and mounted the motor on top with a short 40mm Bowden tube. Heavier print head means more vibrations but i believe the overall printing reliability will be worth a 10mm/s drop in speed. Ive read that a drop of glycerin in the tube will lubricate it and solve resistance issues, also abs apparently self lubricates a bit better than pla. I run a Bowden on a small smartrap that seems ok but i think it because its a very short tube.
Thanks for your response. So I am not the only one to have issues with bowden extruders. Didn’t really think I was. But I don’t see a ton of people complaining about them so I thought maybe some have found a secret that makes them work. Wishful thinking I suppose.
Do you think everyone with a deltabot will jump on the first extruder that promises to mount to the head without causing print failures due to vibrations for the motors starts and stops?
I’ve had many problems. Dry filament improves most of them. Really fast long retractions solve the rest. Ultimaker is Bowden… I think 3mm filament helps them.
Im happy to see others haven’t found a magic formula. I haven’t found much about it either. I think the shorter you can have the Bowden tube the better. Ive bee thinking of mounting it on the gantry so it moves with the y axiz but not the x so only 1 axiz will be affected by the weight and i can run a short Bowden tube. But honestly it would be because I’m bored and want something to fiddle with rather than chasing better prints.
Fwiw, an hour in the oven is overkill. 20 minutes worked pretty well for me.
At what temperature do you dry the filament?
I’ve used 175 as it’s the lowest my oven can accomodate. 200 is fine as well.
@Mike_Miller , that must be Fahrenheit…
oops. Yeah. Sorry. 175C would make it one big pellet.