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Extruder Drive Transmission

Posted by Diggrr 
Extruder Drive Transmission
December 16, 2018 06:22PM
Not wanting to mess about in the other chaps post..

I think I've solved my main problems with gear reduced extruder drives.
*not really a fan of gears in the first place, especially metal to plastic.
*replacement parts are starting to show up online for the geared drives (aka: red flag).
*no love for the MK7 with it's greater contact area on the filament.

I made a transmission so to speak, that bolts between my tried and true MK7 aluminum extruder and the stepper motor, allowing a belt in between to remove stepper artifacts from the prints. I ended up with 20T on the motor and 40T on the extruder end using a 9mm wide closed belt (130mm). The driven shaft is 8mm hard rod, that now sits in place of the stepper's shaft.
I had posted pics in another thread of having two extruder drives, one feeding the other. The gear ratio should have about the same torque (though minus the second MK7 which I rather liked two drive gears).

Bonus: the artifacts that I'd been blaming on my x rail v-wheels all this time (PC mini xtreme v-wheels from openbuilds) is now gone. I had faint diagonal lines criss-crossing the back faces on my prints (when the x is traveling directly towards the extruder drive), but it turns out it was likely vibration up the filament from the motor. They are gone now.

Anyway, play with your toys [often].
open | download - 20181216_175540[1].jpg (451.9 KB)
Re: Extruder Drive Transmission
December 17, 2018 02:26AM
Metal to plastic gears have been used for ages and have in fact plenty of advantages.

To the benefits you noticed due to the reduction, they allow a more compact, lightweight extruder.

GT2 belt plus pulleys is big, heavy and becomes really big for ratio above 2.
Unsuitable for a (non Bowden) direct drive then.

A higher reduction than 2 allows in addition to use a smaller stepper (Nema14 for ex.) making a better use of the power available and even a bigger diam hobbed gear (12, 14 mm) giving more grip with less filament distortion

Smaller belt and pulley would do but not as easily available (1mm pitch)

"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
Re: Extruder Drive Transmission
December 18, 2018 03:24AM
Lighter and compact aren't important to me really, I don't mount my extruders on the machine, but on a separate "tower" of 2020. I do the same on my delta. No loading added to the frame, and no resonance, even if it only manifests as an annoying hum while it's running.

The gear ratio wasn't really important to me, I would have been just as happy with a 1:1. The goal was to decouple the motor via belt, which is something that gears would not have done as well. Plastic and metal gears may have advantages somewhere, but as surely as supply tries to follow demand, replacements are available because they're selling them. You won't find a product available that sells to no one (not for very long).

I would love a source for a good hobbed gear larger than the MK7, specifically made for 1.75 filament.
The dual extruder I'd posted before was just to get enough power to pull a large roll with weak drivers at that moment in time, but in that experiment I discovered the lowered filament distortion is an advantage that I may return my attention to one day. My weak drivers were replaced, and weren't an issue any longer.

For now, I'm quite happy with how this turned out. My objectives were met surprisingly well. Now to design the sturdier Mark 2, as this one of course over time will distort, and as I said, I'm not happy with running the motor pulley out on the end of the stepper shaft. I modeled them .5mm closer to leave some light slack in the belt and lessen the side-load just to get on to what I was after.

I wasn't trying to coax anyone to follow..I'm quite happy being alone. winking smiley
Re: Extruder Drive Transmission
December 19, 2018 07:46AM
I am intrigued with your idea. Do you have better pictures that show the parts? Or video? Seems a clever idea!
Re: Extruder Drive Transmission
December 19, 2018 05:48PM
Here's an exploded view made with spare parts.
2 F608ZZ bearings from VXB on eBay
1 8mm hard shafting from Zyltech also on eBay
1 40T-9mm pulley from RobotDigg
1 20T-9mm pulley from RobotDigg
1 GT2-160x9mm belt from RobotDigg
1 MK7-1.75 8mm ID extruder gear from RobotDigg

Not shown are two 8mm spacers (washers) that go between the 40T pulley and each bearing, from the local hardware store. I assembled the parts on the shaft and used the flange to flange outside measurement for the inside width of the printed box.
Since the extruder is made to mount straight to a motor, I just modeled two motor mounting faces with enough space in between them to get the centers at 51mm for my belt size. Hard to see in the pic, but it's two separate pieces printed flat with no supports, and I touched the posts with sandpaper and glued them facing each other with acetone (it's ABS). I was working on settings for a new filament yet, so the left half has some issues that are corrected in the right half.
I cut flats on the shaft with my Dremel to lock the pulley and the extruder gear in place with their grub screws, it's important that the shaft not be allowed to move laterally.
By coincidence, the bearings and the motor "nose" are both 22mm, so there's less to fuss with when modeling.

You can probably use off the shelf parts with 6mm belt, but since I use 9mm on all my other things, it lets me reuse 'em later.

Edited 2 time(s). Last edit at 12/19/2018 05:54PM by Diggrr.
open | download - 20181219_172444[1].jpg (438.1 KB)
Re: Extruder Drive Transmission
December 21, 2018 04:56PM
I like it. But more pictures good man smiling smiley. Don't be stingy! I'm working on my own variant right now.

Edited 1 time(s). Last edit at 12/21/2018 04:56PM by Holy1.
Re: Extruder Drive Transmission
December 22, 2018 03:35PM
Lol, No Problem.
Let me know how it goes for you!
open | download - 20181222_152509.jpg (472.9 KB)
open | download - 20181222_152554.jpg (502.2 KB)
open | download - 20181222_152633.jpg (498.5 KB)
open | download - Model.jpg (73.9 KB)
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