Dual Drive Bowden Extruder

by invent3d May 22, 2015
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Thanks for this design! I made one, but rather than search for mk8 gears with shallow enough groves, I did a mk8 gear, and then a 36tooth 11mm gear on the other side. https://www.amazon.com/gp/product/B01J5ON2Y2/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1. I should probably change the gear ratio on this side since the 11mm gear has a larger radius, but seems to work pretty well.

Do you wish to share the files in an other format so one can adapt them? I want to mote the motor slightly so I can fit an planetary gearbox.

I would also like to modify the connection to the teflon tube.

great design, have you dont some test if the improves the actual vs commanded extrusion amount?

Well as long as nothing is slipping your actual extrusion should always match how much you asked for. You can quite easily establish your maximum extrude speed for your setup by printing something like a 20mm calibration cube and just increase your layer height and print speed until you start start seeing under extrusion.

My favourite models for testing extruders are the 20mm calibration cube and the hollow pyramid. The hollow pyramid is really brutal on a 3mm bowden setup because of the repeated retractions.

Am I correct to assume that I can use the MK8 version with 1.75mm filament? or are the gears too far apart for this to use it unmodified? I already ordered the MK8 drive gears and the bearings. For now i am still looking for a place to buy the shafts. Which ones do you use? and how long are they?

Off the top of my head I think it will work, but I haven't tested it. The Mk7 version definitely has enough travel that the two drive gears will touch, I'm pretty sure the Mk8 version should too.

The main thing to check is that if you put your two drive gears together side by side, you can actually pinch the filament between them. If the hobbing on the drive gear is too deep then the filament may slip through without being gripped. And it will depend very much on where you get your drive gears from, with so many clones and copies I have never seen two the same from different vendors. I just tested with my Mk8 drive gears and it looks very marginal, but then I'm pretty sure these were sold as '3mm filament' drive gears so the hobbing may be different to yours.

I also don't have much experience with 1.75mm filament in geared extruders, I'm not sure if the gear ratio will be too high. I guess you'll just have to try it and see!

i will! atm i have huge issues with my 800mm bowden /wade setup... clogs up all the time. I wouldnt even think about using my volcano atm. hopefully your extruder will solve it all :) one more thing: Is there a lever or something to quickly swap filament? The new bondtech extruder has that (And a corrosponding pricetag..)

There is indeed a lever. It's not in the photos but the current models have a spot where you can take the pressure off the drive gears to pull your filament out. How hard it is to do depends on how firmly you have the frame bolted down and how hard you have your springs set.

I forgot to answer your question on shafts, I just use 5mm steel or stainless bar cut to length. The 3 shafts are 75mm, 80mm and 85mm long.

Thanks! well then ill go ahead and order the rest. I'll make sure to upload some pictures :) (and please consider adding those measurements to the description. I bet the next guy will be thankful :) )

Yup, ive been meaning to tidy up the documentation. I've been busy working on a triple extruder version for a diamond hot end, should have models up in the next few weeks....

Look forward to seeing your pics!

my mk8 drives just arrived... i think i have a problem: the gap bewtween them is too big.. 1,75mm filament slips through pretty easily... any suggestions? (Note: I do not have access to a drillpress)

Ah, damn. I was worried that might happen. I'm not sure what you can do with those without any tools. Perhaps one of the alternative drive gear designs that use spikes or flat teeth rather than hobbing?

I guess I will look for someone who can hob me some bolts :/

I think trying to do a dual drive with 1.75 filament any hobbing will be too deep. I'd look at something like this: http://m.aliexpress.com/item/32249229301.html?productId=32249229301&productSubject=Wholesale-2pcs-lot-Makerbot-MK7-MK8-Drive-Gear-Reprap-Extruder-Prusa-i3-Impressora-3D-Printer-Part

And maybe just file a very slight groove so the filament sits in the middle, but you might not need to. The dual drive extruder should locate the filament pretty well.

hobbing does work. take a look at the bondtech extruder

Just checked it out.They have custom made drive gears with the correct hob depth (and also gear teeth on the back to drive the two gears). You could definitely hob yourself a set of drive gears that would work, but you may not find anything off the shelf.

Well... I'm a little bummed. Asked at the reprap forums most of them told me that this is unnecessary and whatnot. which is probably true, since a new mk8 drive gear basically fixed all my issues. BUT: more force is always nice and since my current extruder is ungeared and I am now infact get missed steps (Way better than damaged filament!) and I also printed / ordered all of the parts for your extruder, I was still looking for drive gears that would work.
I found those: http://e3d-online.com/Hobb-Goblin-5mm
Will get back to you once I tested it :)

yeah probably not. Maybe someone in the Reprap community can help. I'll take a look.

Looks good, I think I am going to give this a try. What size nuts/screws are you using to hold the gears on the shaft? Typically its M3's but want to be sure. Have yet to find a place locally in the US that sells m3 set screws....

M4 nuts and set screws for the gears. I try to avoid M3 bolts unless absolutely necessary, because the nuts spin in the slots unless your tolerances are spot on.

I also recommend a blob of loctite on the motor gear set screw, mine tends to work loose as it gets thrashed around with retractions.

Oh and also print at least the motor gear with 100% infill if you can, its under a lot of torque and you need to be able to do the set screw up tight without distorting the gear. The other gears aren't as bad, but I now print all my gears with 100% fill just to be safe, it actually doesn't use much more plastic since the big gears are mostly hollowed out anyway.

Guess what guys, MK2 models are up!!!

My first version got a bit hacked up in the prototyping stage, so I am just printing a nicer one now. Ill get some photos and hopefully a video up shortly.

I'm in the process of printing this extruder since I like it alot but now I saw your comment on a MKII version in the works. When is it finished? Do many parts differ? I have printed the gears, should I wait for the new files or continue with the existing ones?

Sorry, I have been away overseas and didnt get the mk2 parts up before I left. There are no common parts between the two. The main decider will be bearings, you need different sized bearings for mk2, so if you bought bearings for mk1 maybe stick with that. Apart from that I think mk2 is better in many respects, its a complete redesign.

I haven't bought the bearings yet and I'm not in a hurry so I'll probably wait for the mk2. While searching for MK7 drive gears I found that there are MK8 drive gears as well. It seems the difference is in the hobbing pattern with other dimensions staying the same so I guess MK8 drive gear would fit your mk2 design.

Either Mk7 or Mk8 is fine, mk8 will give a higher gear ratio but a bit less traction on the fillament. Be careful with cheap drive gears, i bought some mk7's from ebay and they were junk. I made my own instead, if you can make a hobbed bolt you can make a drive gear with more or less the same procedure.

Very nice design! I too have made a big delta, but with 1.75mm: to be honest, with a RobotDigg drive gear (check them out, they're got amazing grip, very sharp!) and a modified Wades extruder, it pushes very well, but it tends to chew the filament when I try to go too fast (faster than 200-250mm/s just doesn't have time to melt fast enough in the hotend, so the drive gear scraps away during a millisecond!)- how do you adjust the tension on the filament?
On the other hand, I've been considering trying to make a dual-pinch NEMA 14 direct extruder (with these RobotDigg gears!), as I'd MUCH prefer a direct drive extruder, but on the delta (as you've probably found out) a single NEMA extruder cannot be centered, however, I have yet to sort out the tensioning problem - even if I managed to make it with perfect calibration between the gear teeth, eventually I'd need the ability to adjust extruding pressure (when using materials of different hardness, i.e. NinjaFlex, or Woodpile).... any ideas??


PD All said, still not sure how to get over the limit of how fast the hotend can melt material - I think that once reached that limit, either the extruder drive will miss steps, or the filament will be scraped, as it just cannot go faster - the only thing then is more temperature!

Adjusting the tension on two rollers is a tricky problem. Its partly why my design has so many gears. That Robotdigg drive gear looks interesting, I havent seen those before. As you go faster you will always find more limits, whether its drive gear grip, motor torque, heater power, or hot end flow rate. You just have to work out whats limiting you and fix it =) Though I would say once youve hit the max flow rate of your hot end thats probably a sensible place to stop. What extrusion volumetric flow rate can you achieve with your setup (in mm^3/s)?

How do I calculate that? I've never thought to try that out, all I know is that with a larger nozzle (I've tried from 0.3 to 0.6, which I now keep), you get larger plastic flow, so the extruder has to go faster for a set layer height - as I'm trying got build 30cm parts, I'm trying to get as fast as possible, so a large nozzle gives large layers = shorter build time, but, as mentioned, more problems with too high plastic flow when the hotend can't keep up - now that you ask, it seems clear that there would be a volumetric number that would be the max, and a smaller nozzle (with smaller layers and less plastic coming out the hotend) would be able to print much faster speed, but over all print times would probably be the same... that ties in with my observations, but I never thought to make the calc!
I've actually just changed to a Prometheus from a E3D v5, as the E3D, in addition with the high retraction length on my bowden setup, has a load of sticking PLA problems, that go away for a while adding a drop of oil, but always come back :-( so far the Prometheus hasn't had any problems related to retraction, but I've only had it on a week! It does as well seem to support higher printing speed, so that's nice too!

Anyone working on improving their extrusion speed should read this as a starting point:

Ill add it to the instructions up the top =)

If you use Cura to slice your model it actually tells you your volumetric flow rate, or you can work it out from your extruder feed rate and the diameter of your filament.

I like this, have you had any problems with gear backlash?

Not that I have noticed. I dont think backlash should be an issue since you only drive in one direction, your retract might be a bit sloppy but you should end up in the same place when you go forward again.

One issue with the design at present is that there is no adjustment on the gears (the motor has some, but the secondary drive gear has none). The gears are modelled to mesh at that distance, but your backlash depends on how accurately you can print them. They came off my printer about 0.5mm oversize which meant they have very little backlash but were quite tight when I first assembled it. I was missing steps on some tight spots for a little while till they wore in a bit and sorted themselves out.

Wow... you read my mind!
I was just thinking of designing something like this. Want to push filament fast thru an E3D Volcano and was also worried about chewing it up.
Can you give some details on how you made the hobbed bolt heads?
Look forward to downloading your files!

Damn, I should have seen this coming. I didnt take any photos when I hobbed the bolts. But ill take some next time I make a set. Ive added a bit on bolt hobbing to the instructions.