I think the concern is about how well it bites into the filament. Can you show a picture of the “bite” on filament after it’s passed through the drive?
QU-BD also lathed a trough into their pulley gear and it worked poorly, especially given how slippery brass is, because the actual contact surface is smooth. The teeth grooves don’t matter unless you crush the filament to get actual bite. A cut thread hob like a MK7 style pulley worked far better, it was a lot more efficient and less stressful on the motor.
I’m interested in the bite profile as well. Removal of material, deformation of the filament, any grinding or sliding of the gear edges against the sides, etc.
I’d love to turn something like this into my primary, go-to extruder. But I’d have to be sure of its applicability to all of the other filaments I use too.
Im Ignacio from Recreus, first of all many thanks for.you comments. I would like to explain you a little bit more about our new extruder.
I have been testing with Pla and Abs during the last week and they really works well at High speed. Even I’ve been printing abs, during the printing process I cutted the abs filament and put inside Filaflex and the elastic filament push the abs and still printing filaflex ( WITHOUT STOPPING THE PRINTER).
Also during this week I want to mount a delta printer and try the Rec - extruder with our hotend in bowden style. Im pretty sure that it will works at high speed. I will notice you as soon as we have results.
Hello @ThantiK , we are sorry,at first time we are going to sell only the full package. Because we think that the success of elastic prints are both parts extruder and hotend. Maybe in the next couple of months we will upgrade for another hotends.
There is no crushing or deformation of the filament. The grip strength comes from the dual sided drive (spring compression) as well as the increased surface contact areas. The groove in the teeth grips the filament at the front and back as well as the left and right. which is perfect for full constraint of flexible filaments as well none grinding of rigid filaments.
@Steve_Wood_Gyrobot I’m more interested in a lighter color filament, with up-close pictures of the filament where it touches the gear. That video, you can’t see anything other than…it extruded. I have a couple of very similar gears at work right now though, and I think I’m going to try and prototype a similar system.
That’s not hobbed, those are the remaining grooves of the gear after turning a smooth valley. The actual contact surface doesn’t bite into the filament at all.
The groove is cut below the lowest point in the valleys between teeth, and there are perpendicular cuts within this groove that don’t match the pitch of the gear’s original teeth. It’s quite possibly the worst hobbing I’ve ever seen (with narrow cuts and huge flats on the tops of the “teeth”, like putting cow’s teeth in the mouth of a shark), but it’s there.
@Whosa_whatsis Hahaha brilliant, but at least it will never strip the filament, with little sharp teeth grinding through like a file. This is also an important property. Mostly the grip is attained by the larger surface area all round the filament both, left right and importantly front and back too, which should not be under estimated. But a great comment, love it.
OK, I see what you mean, but I still contend you need actual teeth that bite, not valleys that don’t add friction or bite. Brass is about the slipperiest metal available, and you still have a smooth contact surface. This hasn’t demonstrated an increased pushing or pulling force over existing designs.
One tactic one can use is to dial back the motor current so it stalls rather than strips. But that’s besides the point. I’ve done a single hob for a long time with only one strip a few months ago. That was because the plastic was sitting melted in a hot end for many hours. Other than that, a single hob did just fine. A second drive pulley would seem to be a band-aid for problems in the hot end, such as too much heat, not enough, or actual debris which a second pulley won’t clear anyway.
@Jeff_DeMaagd Ok, maybe you wont be convinced on this one, despite the fact that it works and has many hours printing under its road test with PLA and ABS with no stripped filament either.
It is not designed to give “better” grip than the current hobbed solution for rigid filament, it was designed the be the best constrained solution available for Filaflex type materials which buckle so easily. Which incidentally is the topic of this post. If flexible isn’t in your bag then carry on as you were with rigids.
It’s obviously a simple change to hob the teeth deeper if we want “super grip”, but as you said it’s a band aid for hot end problems, so why bother and increase the risk of stripping filaments?
I think the risk is super low. I’ve had one strip in maybe a year? And that was with hot plastic sitting in the hot end for a few hours. And my single hob extruder does flex with impunity. I contend flex compatibility is a very simple mod to most extruders.
A friend’s single hobb extruder managed to hold up the weight of an entire 3D printer dangling by filament. So, given all that, I’m still not seeing the benefit.
I can only confirm @Steve_Wood_Gyrobot in his findings. Flexible materials are a bitch to print and tight guidance of the filament is key, especially if you don’t want to wait much longer on prints. @Jeff_DeMaagd are you trying to print 3mm filament or 1.75? 3mm is not half as problematic as 1.75. It tokk me a while to come up with an own design for this http://www.thingiverse.com/thing:336444 that does not look half as good as Steves.
@Bjorn_Marl I used a continuous PTFE tube in my extruder like in your design, previous to this new double drive solution. It is a very good solution for flexibles, but I could still only print at about 45mm/s before the MK7 hobbed gear started slipping and miss feeding. This new version works at over 100mm/s straight out of the bag.