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david.f42
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Extrusion gears grinding black PETG idler part into dust. Probably on yours too.

Mon Jun 11, 2018 6:43 pm

I had reprinted part of my printhead in white. Whenever I've opened the extrusion idler, I've seen a pile of black dust. I actually had already cleaned it off before it dawned on me that I should take a picture, so here it is, which shows a wideshot and then a closeup with some of the traces still left:
wideshot.jpg
wideshot.jpg (455.98 KiB) Viewed 660 times
closeup.jpg
closeup.jpg (373.36 KiB) Viewed 660 times
I'm pretty sure it's ground black plastic from the idler (from the original kit):
grinder.jpg
grinder.jpg (492.22 KiB) Viewed 660 times
That gear piece has nothing to prevent it from grinding against the sides (nylon washers would maybe help if the part were redesigned to make room for them), and so it grinds off the black plastic. Well, why is that a problem, you ask? There are fans moving air around. All it takes is for those plastic bits to land on the filament, or go in the hole which leads to the hotend. Those are PETG bits of plastic. If you're printing PLA, they won't necessarily melt, possibly leading to... a clog. There, I said it.

Since the original kit is all black, you might not even notice this black dust against a black background. So, maybe no one is aware of it. As you can see in the last photo, I am now going to try to mitigate against it by using some sparing amounts of white lithium grease. It's not a good solution, but it will have to do until someone comes up with a better fix (like maybe a redesign with washers on either side or perhaps something better still).

Comments/suggestions welcome.

BEST ANSWER by martin.w15 » Thu Jun 14, 2018 11:36 pm
As I now have spare nylon washers I felt safe enough in removing the idler from my MK3 for a close look.
Image
Image

As well as the expected brown of rust in the lithium grease small amounts of near black plastic can also be seen matching the colour of the printed part. All though it turns freely when not under load I suspect it grinds lightly when under the tension from the springs.

As a result I have added some tolerancing clearance to the part under the gear.
Image
STL of Extruder Idler W2
Autodesk DWG of Extruder Idler W2

Regards,
Martin

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martin.w15
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Re: Extrusion gears grinding black PETG idler part into dust. Probably on yours too.

Tue Jun 12, 2018 12:06 am

David,

The extruder body needs to be printed in black. The filament sensor requiers this to work.

Regards,
Martin
Last edited by martin.w15 on Tue Jun 12, 2018 2:00 am, edited 1 time in total.

martin.w15
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Re: Extrusion gears grinding black PETG idler part into dust. Probably on yours too.

Tue Jun 12, 2018 1:32 am

Here is a redesigned extrudler idler with room for nylon washers.
Image
STL of Redesigned Idler
Autoddesk DWG File of Drawing

Regards,
Martin

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david.f42
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Re: Extrusion gears grinding black PETG idler part into dust. Probably on yours too.

Tue Jun 12, 2018 8:42 am

Wow! Fantastic! You've got amazing talent. And fast too. Thank you!

:D :D :D

martin.w15
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Re: Extrusion gears grinding black PETG idler part into dust. Probably on yours too.

Thu Jun 14, 2018 7:11 pm

David,

I have just been looking at the extruder Idler again.
extruder-idler W1-A Section.jpg
extruder-idler W1-A Section.jpg (142.53 KiB) Viewed 284 times
The rubbing that is causing your problem may not be from the ends. Does the Idler in the new part spin freely because looking at the section I just added to my drawing (I tend to review my work after a couple of days,) there is no tolerancing between the idler gear and the printed part.

Regards,

Martin

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david.f42
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Re: Extrusion gears grinding black PETG idler part into dust. Probably on yours too.

Thu Jun 14, 2018 9:59 pm

martin.w15 wrote:
Thu Jun 14, 2018 7:11 pm
Does the Idler in the new part spin freely...
I don't know. I'm waiting for the next time I disassemble my print-head to try out your new part. Not sure when that will be.

martin.w15
Posts: 140
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Re: Extrusion gears grinding black PETG idler part into dust. Probably on yours too.

Thu Jun 14, 2018 11:36 pm

As I now have spare nylon washers I felt safe enough in removing the idler from my MK3 for a close look.
Image
Image

As well as the expected brown of rust in the lithium grease small amounts of near black plastic can also be seen matching the colour of the printed part. All though it turns freely when not under load I suspect it grinds lightly when under the tension from the springs.

As a result I have added some tolerancing clearance to the part under the gear.
Image
STL of Extruder Idler W2
Autodesk DWG of Extruder Idler W2

Regards,
Martin

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