Direct-drive extruder with nearly no space between hotend and hobbed bolt

In the last months, developing the nozzle pressure control feature LIN_ADVANCE for Marlin FW, I more and more realized that it’s essential to have nearly no free filament length between the hobbed bolt and the nozzle. The longer this distance is, the more unwanted effects happen to the filament like buckling and compression (like a spring) leading to print quality issues like gaps between perimeters at high speed, underextrusion on line starts, overextrusion on line ends, hughe necessary retract lengths or even the missing ability to extrude flexible filament.

While LIN_ADVANCE uses the extruder stepper to compensate for the filament compression, it’s only a work around in the end. The best way would be to have an extruder that has it’s hobbed bolt directly above the hot end filament entry bore.
On a stock TAZ 5 extruder this would mean lowering the hobbed bolt up to 25mm, reducing the free filament length from ~85mm to ~50mm (30% reduction).

Yesterday, I stumbled about this extruder on Thingiverse. I love the design: Compact and hobbed bolt and hotend are nearly at the same place. But I don’t like an ungeared extruder for 3mm filament…

So here comes the question: Does someone here knows something like this for example with a gregs wade extruder? Or has somebody already made some experiments with more compact designs?

I agree, the fillament path should be reducable from the hobbed section down to the melt chamber. The thermal break and the mounting arrangement are two of the limiting factors that really need to be addressed. I’ve experemented with shortening the lower path a bit, and i’m working on a solid fillament follow up to this extruder of mine: but even that one could be lowered. The hotend itself should theoretically be able to be made shorter. The top of the hotend should be the hobbed bolt / gear / etc mounting location, countoured to fit the fillament chamber, still allowing for an idler for tension adjustment and cleaning, and with a much wider heat sink / integral mounting flange to attach to structure, possibly with integral gas or water cooling mini loop. The approach taken by the Toranado extruder is a good one but the motor and gear setup doesn’t have enough horsepower to match the Wade extruder fully. That being said, I think the wade gear size could be reduced (or my preferred zero backlash belt option) by at least 1/4th without reducing print quality or speed. Possibly further.

I really like the drive option found on the Bondtech extruders. as the dual hobbed gears make for much stronger and more consistant extrusion, while eliminating most causes of fillament stripping. I don’t necessarily like the planetary gear NEMA motors as I feel the additional gearset leaves a possibility for a bit of lash that you don’t get in a belted or a direct drive design. Possibly less than you would see with a Wade gear setup though.

The J head style mounting flange design is very popular, but it is really not ideal for what we are trying to do, which is attach as short of a metal hotend to structure as possible with as little possibility for deflection as possible and as little mass as possible. It’s too tall. If we took all of that metal and made it into a wider heat sink plate thing, probably threaded to fit 3 or 4 M5 bolts or maybe even a dovetail slide in mount, possibly adding in a ceramic heat break plate it should be possible to make a much shorter, somewhat wider hotend that is more stable, has a shorter run to the melt chamber to minimize PLA bore lock, but still heats and prints like a hexagon or an E3Dv6. I even have most of a design for such an extruder worked up. My mill isn’t up to cutting one yet though. I think there are also efficiencies that can be had at the heat block as well. A ceramic disk to eliminate the weak point between the heater and the upper barrel possibly, maybe a hollow cylendrical heater core that the fillament passes directly through instead of the side mounted units we use today to lower the mass and raise the efficiency somewhat? a pasta extrusion die style deop in from the top nozzle to eliminate threads and leaks there?

I think if you took the core of a bondtech extruder, coupled it with my theoretical shorter hotend, added something like the ducting from the Toranado design, possibly with a copper coil filled with argon wrapped around the barrel to a heat exchanger on the back somewhere, and then added either something similar to my belted powertrain or some other zero backlash powertrain option, you would have a very compact, very accurate extruder that would eliminate most of the corner blobbing and layer inconsistancy that we see with today’s best options on small items. I think even if I get the prototype for my theoretical hotend exactly right the first time, I’m still looking at a few $100 to make something workable. And even then it may end up too complex to manufactur efficiently, or may have a very low adoption rate.

Thats my $0.02 cents on the subject anyways.

A compact direct drive extruder would be my preference also. Personally, I like Printrbot’s simplistic design… I haven’t tried the new gear driven model.

Doing some research, it seems as though a direct drive with no gearing from the stepper may not be enough to push 3.0mm filament through the hotend. This could be a legacy effect of ceramic hotends… E3D’s Titan supports 1.75 or 3.0mm filament with no gear changes in the extruder.

A very good writeup percet :slight_smile: I had simmilar thoughts, but not that detailed because I know I have no chance (tools) to ever bring them to reality. In fact I would wish e3d would develope something like that. I have the feeling everyone of the “big” manufacturers accepted the e3d v6 and similar as perfect design - there was nothing realy new in the last years… If you start selling such hot ends I would by one I think :sunglasses:

I wasn’t having the bontech extruder in my mind anymore, in fact it looks as it also has a nice short design. A tad more steps/mm would be nice, I like the ~800 of the TAZ extruder. Sad that they don’t sell the gearbox on it’s own except you already own the old modell…
Regarding the backlash of course it’s always nice to have none. But I think it’s not that bad on the extruder. During printing, forces eleminates the backlash. It should only result in some 0.1mm extra retract distance.

We have such printer with 3mm and no gearing extruder at work, a German Reprap X400. It can extrude, but you should never try to print too fast and it starts slipping/skipping steps very easy. I realy don’t like it!

Decided to play with my extruder design. I have a kossel style round E3Dv6 mounting plate that I think I want to use as the base, because I don’t feel that ABS will be rigid enough on its own. With that in place, I think this is about the closest I can get the E3DV6 to the hobbed thingy chamber with a stock E3DV6. This is still a very rough mockup at this point, and it is missing many important features. Bit it gives an overall idea of a workable layout. The motor mount and belt section will end up shorter by another 3mm, but aside from that , that section works well. There is no provision for mounting it yet, the lower duct half thingy doesn’t exist yet, and I think the area above the hobbed chamber will need to get a bit taller to accomodate the slide up idler latch, possibly as much as 6 or 7mm. No idea how I am going to get the plate mounting nuts in place, possibly side load slots.

The new idler arrangement seems like it should work well assuming I figure out the mounting slots. Those might end up being a separate assembly, not sure yet. Margins are going to be really really tight on this one.

The hobbed chamber bottom to E3DV6 top section is going to be about 5-6mm long. I’m pretty much just thinking a straight ABS hole is fine even for flexible fillaments for that distance. Adding a PTFE liner right there might reduce friction, but its such a short run, I don’t know if it will be worth the effort to put it in. I’ll probably poke at the whole design this week, and maybe have a prototype next weekend. I’m planning on having one mount that will fit a stock Taz, and one that will be an entirely new concept that will fit the openbuilds mounting plate. I am concerned that the entire extruder may end up too short to reach the bed without a major change there too, but we’ll deal with that if it becomes an issue.
Streudalstruder.stl (679 KB)

Very intresting, let’s see how this grow up :smiley:

That’s an interesting design. Looks like it still needs the Wades gear on the stepper, which is what I’d like to avoid. My other thought was how the positioning of the stepper could affect the center of gravity of the extruder… but then since the extension is in the direction of the travel (X-axis). Then it boils down to clearance within the frame (more for a dual extruder setup).

It would be interesting if the design stepper could be mounted directly behind the filament path and using a direct drive gear instead of the hobbed bolt. That could introduce other problems with the hotend further from the X-rods/openbeam.

Technically its a belted design, not a geared one. But yes, it’s not a direct drive. I don’t think a 3.00mm direct drive extruder with good results is possible with a nema 17 standard length motor. Maybe one of those extra long ones? There just isn’t enough torque there unless you slow it way down.

Got the other half of the idler and the top latch done, as well as the mounting screw nut holes. Next up, the top is going to need to be 5-6mm taller to accomodate the idler latch slide, and I think I may have to extend the front of the latch 3 or 4mm to make sure there is enough room for the front slide without getting too close to the fillament feed. Then I can start adding the mount hardpoints, and building the lower section that will surround the E3DV6 itself for ducting and cable management. Once the top part is done though I can start printing it. I have a second set of bondtech extruder core hobbed thingies and belts and pulleys, but I need to go grab a bolt for the assembly (or temporarily poach the one from my flexistruder. ) I’m not sure I have another set of fans around here either, I may need to go grab some of those.

Well, the concept works. and it seems to work well. I have a few problem areas I need to fix (the upper nut shafts are too tight) and a few refinements to fit the mounting plate and the lower fan unit, but it’s functional as is as a prototype aside from the idler latch. I’ll probably go ahead and make my own thread for it for now, I’ve hijacked this one enough. but here are some pictures of it before I do:

Up next, I’m changing the upper mounting hole for a direct bore through bolt rather than a heat set insert, and i’m adding a far motor mount side bracket of some sort. Then the spacing for the actual mount itself and the lower duct begins.

Flex3Drive has a 40:1 reduction gear assembly that works for direct drive extruders. It also allows you to move the motor off the carriage.

Awsome! I was thinking about such a system in my first printing days, discovering the pro and cons between bowden and direct drive systems.
If (and that’s a hughe if) the shaft is as stiff as they write (<1 missed step of a normal extruder) and there is nearly no play in the worm drive that should be a nearly perfect drive system. But why I was never reading about this ever before? I also miss some real live pictures and videos… Nearly everything on their page is computer generated pictures.
Saramos, are you using one of this?

Combining one of this drives with a compact e3d mount like in piercets design could be awsome :sunglasses:

I ordered their flex3 drive 3rd gen extruder to use with the Hexagon, but have not yet received it. Then I will need to make a new mount for the taz. It’ll probably take me some time to get it all done, I’m not real fast on projects, just ask my wife!
If you search flex3drive on youtube, you can find some videos.

The videos don’t show much and i think they show an older version.
It would be great if you could write something when you get it, for example compare backlash with original taz extruder and how easy it is to change the filament. I have not understood how is possible to adjust the tension up to now.

Do you plan to reduce microstepping to keep esteps/mm in a reasonable range?

Reducing micro stepping is something I had not yet even thought of. My goal is to have very fine control of the filament feed for high resolution printing. I have been playing around with a .15 nozzle printing at .04 layers. I also have a .10 nozzle that I have not tried using yet. I also switched to a 1.75 hexagon. At these sizes, I’m not sure if I will need to reduce the micro steps, but I could see where that may be advantageous for normal to high speed printing with .35+ nozzles. I have yet to do Piercet’s open rail upgrades. I was hoping that moving the motor off the carriage and reduced size/weight of the extruder would help eliminate most of the sag probem. I will certainly do a thorough review of the setup and post videos.


For adjusting the tension, on the taz, the idler and tension adjustement screws are on the same side of the tension arm pivot. On the Flex3, the adjustment and idler are on opposite sides of the pivot. It look like their current version uses a cam adjustment, but comes with an optional screw adjuster as well. One video shows the adjustment screws for backlash. The drawing doesn’t show it, so I’ll find out when I receive mine.