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3:1 Geared Bowden Extruder

by FerociousDiablo, published

3:1 Geared Bowden Extruder by FerociousDiablo Sep 22, 2017

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Summary

Here is a design I have been working on for a 3:1 geared bowden extruder capable of pushing flexible filament such as TPU.

I printed everything with 25% tetrahedral infill in cura. 4 top/bottom/wall shells. 0.2mm layer height. Some of the fittings are a bit tight and some parts may need some cleaning after printing. Use supports everywhere 10% lines in cura as they are quite easy to remove and help with some parts.

1: Attach the gearbox part to the bowden motor mount (I use: https://www.thingiverse.com/thing:2369063) attached to your frame using either 4xM3x10MM bolts or other suitable bolts.
2: Fit bearings into main body and top cover, they should push all the way in with a little persuasion.
3: Fit M5 bolt into spur gear and push all the way in. Slide one of the washers on after the spur gear.
4: Push M5 bolt with spur gear attached into bearing in main body from rear.
5: Fit Mk7 extruder gear to M5 bolt and line up with filament holes in main body, it can help to mark where this lines up with the holes and file a flat spot for the grub screw but this is not essential.
6: Assemble arm, put M3 nut into hole in handle and thread 20-25mm M3 bolt in to it from the other side. Put other M3 nut into hex hole on adjuster cog and bolt onto the 20-25mm bolt. Push larger bearing onto the stub at the other end of the arm and then push the stub on arm retainer into the top of the bearing.
7: Attach arm bushing to main body with M3x10mm Bolt from rear. You may need to clean this part up a bit so it fits nicely into the hole on the arm. Slide assembled arm onto the bushing once attached and insert spring between the adjuster and hole on the main body.
8: Fit top cover to main body using 4xM3x10mm bolts. Put M5 washer on M5 bolt on top of bearing in top cover then bolt M5 nylock nut onto M5 bolt. Do not overtighten. The bolt should be able to turn freely with no pressure on the arm.
9: Fit assembled extruder to gearbox using 4xM3x10mm bolts, paying attention to the orientation of the push on gear for the stepper motor. It will only run one way. Attach the pneumatic couplings to main body. You may need to use a spanner as they are a tight fit at first.
10: Calibrate extruder steps per mm. Mine is 316.66 for PLA and 327.59 for TPU.

Leave any comments and suggestions in comments section please :)

Required parts:
13x M3x10mm Cap head bolts
1x M3x20 to 25mm Cap head bolt
2x M3 nuts
1x M5x45mm bolt
1x M5 nylock nut
2x M5 washers
1x Stock Anet A8 extruder spring. (about 8.5mm diameter and 20mm long)
1x Mk7 extruder gear. 13mm tall, 12mm OD, 10.6mm ID, 5mm bore
2x PC4-M6 pneumatic couplings
1x 608 bearing (I used 608-ZZ)
2x 625 bearings (I used 625-2RS)

Check out this 3D printer support group for help with your settings or anything else printing related: https://www.facebook.com/groups/1843740479205162/

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Printed it, but I think my settings were a bit off on my printer cause the holes for the screws are too big to actually thread the screws in, and have them catch into the material. I’ll try printing again with different settings, so no fault there

I did manage to print for a good 10 mins with it though, seems like a great unit while it worked, but had to switch back so I can print a bunch of spares of the small 12 tooth gears out of the strongest material I had on hand. Carbon fibre ABS. Seems with the other materials I used, including nylon, that the gear can’t handle the 730 steps/100mm that I needed to set up for. after while, the D becomes round, and won’t do anything but freewheel on the shaft.....granted 730 for esteps is practically insane, but stock I actually had at 238.39, which is nuts as well. I fear if I predrill for a grub screw, it would damage the profile, and in turn damage the other gear as well, due to the herringbone shape. I will attempt to remix the gear with a collar, which will accomodate for extra face strength as well as provide a space for a grub screw.........might take me a little while to figure that out, but I think there would be enough space there if I reuse the grub screws from the stock extruder drive gear

The holes would be too big if you used less than 4 walls I think. :)

Good idea with the collar / grub though for the stepper gear. Although I think when you fix the walls it will be a bit more grippy on the axle

I'm trying right now with a .3 nozzle and 7 perimeter

that did the trick on both parts.....everyone this is the solution if you have problems with the holes and gears :)

Hi. I have printed everything in PLA but can't seem to get it to work properly. I have to manually put force onto the filament or the handle so that the gear can grap and extrude with enough force. I just changed over to a MK7 gear since I was using the original A8 Gear before, but this also didn't help.
Right now I have one of my hex wrenches jammed in between the casing and the adjustment nut to enlargen the force with which the filament gets pushed into the gear.
Did you do any other adjustments to your gear or have an idea what could cause my problem?
Otherwise this looks like a really awesome design, thanks for sharing and hopefully I'll get it to work nicely soon.

Oh...I'm using it with a Prometheus HotEnd V2.

It sounds like the extruder gear you have is the smaller type? The one I use is 12mm diameter on the outside.

I did nothing to the parts once printed apart from clean up the supports / brim. Sorry thats not much help :(

Thanks for the quick reply :). My gear is actually 12mm in diameter too. It barely fit and I really had to tighten the little screw so that the gear wouldn't get stuck on one side.
I'll see what else I can do about this.
What kind of Hotend are you using?

No worries, it is very strange :(

I am using a E3D V6 clone on my A8

Looks fantastic! I'm always a bit cautious when buying hardware, do these look like the right gears? https://www.amazon.com/Witbot-Stainless-Steel-Extruder-Printer/dp/B01KJONSRS

Yes they are the same dimensions as the one I am using :)

Hi. Excellent! Can I use flexible filament with this? Thank you!

Yes, I have used with TPU and had no issues. It worked really well. Remember to calibrate extruder steps :)

hello, why a mk7 gear and not a mk8?

MK7 seems to grip the filament better in this application.

Love it... Thanks. About to print it tonight in abs...

Great! Please post a 'make' when completed and let me know if you run into any problems. There shouldn't be any but I have only printed it in PLA so far.

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