slipping filament - motor shaft wiggly

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bill_i_am
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slipping filament - motor shaft wiggly

Post by bill_i_am » Tue Jun 30, 2020 6:16 pm

Everything works great, then I change filament and filament now won't feed...pinion slips on filament. Bite in filament looks OK, but tried different adjustments. Tried a different filament spool, still slips. Checked that pinion set screw was tight - yep. Doing that, I noticed the extruder motor shaft has some side to side play. I don't remember seeing that before. Hard to estimate how much play though, but more than I would have thought. Not sure what to check next...

airscapes
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Re: slipping filament - motor shaft wiggly

Post by airscapes » Tue Jun 30, 2020 7:04 pm

Look in the crack and watch the motor shaft when the filament slips.. if the share is not turning the pinion gear on the motor is no longer locked to the shaft. It is held in place by locktight or some chemical means.. If you find this to be the case just replace the extruder motor with the complete assembly ..Or you can try and redo the chemical binding of the gear to shaft. Just did mine for the second time, and will be getting a new assembly next time.. BTW they sell the gear but the new gear was too looser than the old one..
If the shaft is turning you may be in need of a new extruder houseing.. Ed will come along shortly with some additional things to check.

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ednisley
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Re: slipping filament - motor shaft wiggly

Post by ednisley » Wed Jul 01, 2020 6:58 pm

bill_i_am wrote:
Tue Jun 30, 2020 6:16 pm
then I change filament and filament now won't feed
The new filament may be oversized enough to not quite feed through the plastic block; some folks have found passing a 2 mm (75 mil) drill through the block clears the blockage. The symptom will be the nice gouge carved by the feed gear into the jammed filament.

After long use, the hole through the block can wear enough to let the filament slip off the side of the bearing opposite the gear; the solution is to print (using your dead printer?) a new block. The drive gear can also go walkabout, but, as you're already check the screw for tightness, that seems unlikely.

To diagnose motor problems, put a mark on the shaft visible on the back of the motor and another on the filament drive gear shaft: if the motor is turning while the filament drive gear isn't, then the pinion on the motor shaft inside the planetary reduction gearbox is loose or worn out. Although it's possible to replace just the pinion, IMO the least horrible alternative is to order a new motor and a pinion, install the new motor, then putz around with the pinion; based on what I read here, the latter operation is rarely successful, so you can save some shipping by ordering both at once.

Good hunting …

bill_i_am
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Re: slipping filament - motor shaft wiggly

Post by bill_i_am » Wed Jul 01, 2020 7:08 pm

Ahh, thanks for the insights! Hopefully my Snark won't turn into a Boojum!

Background for any youngsters out there: https://en.wikipedia.org/wiki/The_Hunting_of_the_Snark

Bill

bill_i_am
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Re: slipping filament - motor shaft wiggly

Post by bill_i_am » Wed Jul 01, 2020 8:15 pm

Update:
1. The filaments are partial spools I've used in the past and have been stored cool and dry with desiccant so I think they are OK. They measure 1.75 to 1.80mm depending on where I check.

2. I can not see an opening between the gear assembly and the stepper motor that shows the stepper motor shaft, but I did mark the end of the stepper motor shaft and when the extruder gear stutters/slips the stepper motor does also... NO continuous motion of the stepper when the extruder gear stutters.

3. Looking closer at the problem, the filament stops just as it clears the bearing/extruder gear drive area and starts back into the 3D printed block. This is when the stuttering happens. Removing the block and pushing filament through by hand shows some resistance but not what I would expect to cause the motor to stall/slip. Very subjective call on my part. ( I tried stopping the running extruder gear by hand... dang evidently filament is tougher than my fingers.) I ran the smallest drill bit I have through the block but did not seem to shave out any material. The next drill size up is too big.

4. I reassembled the extruder with a chunk of filament going all the way through the assembly (past the 'blockage') and the filament feeds! This leads me to think that the problem is in the 3D printed block.

5. I am hoping that by assembling the assembly with filament in place I can print a replacement block. I have limited confidence I could print the entire block.

I would ask you for a sanity check but I think I already know that answer, but how is my logic here?

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ednisley
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Re: slipping filament - motor shaft wiggly

Post by ednisley » Thu Jul 02, 2020 3:19 pm

bill_i_am wrote:
Wed Jul 01, 2020 8:15 pm
an opening between the gear assembly and the stepper motor that shows the stepper motor shaft
The only rotating parts you can see are the gear shaft (inside the filament drive gear):
IMG_20200702_095320 - Makergear M2 - filament drive gear.jpg
And the motor shaft (toward the gantry):
IMG_20200702_095231 - Makergear M2 - filament drive motor - rear shaft.jpg
The gearbox has a 5:1 reduction, so the motor shaft turns much faster than the drive gear shaft. If the motor continues to turn while the drive gear doesn't, then the pinion gear inside the gearbox is defunct.

I drew those lines on the shafts & gear long ago and they're a great debugging tool for seeing what's turning in relation to what's not. Here's an earlier version of the drive gear in free air:

Image
the filament stops just as it clears the bearing/extruder gear drive area and starts back into the 3D printed block
The drive gear & the idler bearing aim the filament differently than the straight-line path you feel by hand, so the end of the filament may be hitting the side of the hole rather than going into it. That can also be due to the plastic block wearing away, but it's hard to tell from outside.

I think you're closing in on it!

bill_i_am
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Re: slipping filament - motor shaft wiggly

Post by bill_i_am » Thu Jul 02, 2020 5:23 pm

Thanks for the images... my parts have now little marks on them also! Ah, good input about the filament path being slightly different from a hand-feed path. It is hard to see, but when I removed the roller bearing it did seem a little 'rough' down where the filament would plunge into the bottom of the filament drive before exiting to the hot end.

I noticed the filament drive block has a metal filament guide down inside the top so I think I will just order a replacement 'V4 filament drive'. The replacement is ABS also and I have been doing just PLA.

Thanks for all the insights!! I will now ride off into the sunset... no news from me is good news. (:-) Stay safe.

Bill

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