What's wrong with my extruder?

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Kingdom3dPrinting
Posts: 8
Joined: Fri Feb 24, 2017 2:19 am

What's wrong with my extruder?

Postby Kingdom3dPrinting » Thu Mar 09, 2017 1:01 am

I've had my N2 plus for about 3 weeks now.

Had problems with extruder block heating up too much during abs prints so detuned stepper ref voltage to 0.65v from 0.9v.

Everything worked fine for a few days but then it started stalling the extruder about 12hrs into an ABS print that I was attempting at 80mm/s (it wasn't actually going that fast due to accel settings)

So I cranked ref to 0.75v, came good for a bit and then came back a few hours layer to the last 50 layers being extruded with only half the plastic required.

I have now rebooted, returned stepper drivers to 0.9v ref and switched the two extruder stepper drivers around (not backwards - swapped positions).

Still have exactly the same symptoms... When doing a filament load, the extruder motor skips every 1 second or so resulting in slow extrude rates.

- It stops skipping if I help it a bit.
- the filament looks fine coming out of the nozzle and is doesn't take much force to help it so I don't think this is a partial blockage problem.

Is the next step to replace the motor?

Is there anything I missed?

What else could be wrong/the cause?
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Jetguy
Posts: 1090
Joined: Tue Mar 22, 2016 1:40 am

Re: What's wrong with my extruder?

Postby Jetguy » Thu Mar 09, 2017 1:08 pm

Replacing the motor is not going to solve anything. If the motor spins at all, skipping steps is never the fault of the motor.
You simply have greater load than the motor can push. Solve the friction issue. That comes in that the stock feeder uses a fixed distance between the gear and the v-groove bearing to grip the filament. Based on filament type (ABS,PLA, PET) that has slightly different diameter from spool to spool along with a different hardness for the teeth to bite into the side. That translates into friction as the motor not only has to push the filament into the hotend, it has overcome the force required to deform the filament as the gear teeth press into the side of it. The holes in the mount are intentionally larger than the screws holding the motor allowing it to be moved in relationship to the mount and thus the V-groove idler attached to the mount. If you don't have enough "pinch" here, then the gear grinds and slips, too much "pinch" (AKA smaller gap) then it takes too much friction force from the motor to basically deform cold filament in the shape of the teeth pressing deep into the side. This varies from filament to filament because again, filament diameter does vary from spool to spool and the hardness changes between filament types. This is why a fair number of us got tired of making these required adjustments and upgraded to Bondtech or other replacement feeder systems. The stock system can and does work. There are people here in the group using it every day.

But, the key is a misadjusted feeder will definitely skip steps or grind filament if the "pinch" is wrong.

Kingdom3dPrinting
Posts: 8
Joined: Fri Feb 24, 2017 2:19 am

Re: What's wrong with my extruder?

Postby Kingdom3dPrinting » Thu Mar 09, 2017 11:09 pm

That all makes sense.

Except it was working 100% (never noticed any skipping) and then it started at one point and continued to skip.

I don't see how it could have gotten tighter by itself and induced more frinctio from that point... There must be something going on that started at that point.

Still could be friction related I guess, maybe something restricting in the hot/cold section below the extruder.

Thanks for the suggestions so far.

Jetguy
Posts: 1090
Joined: Tue Mar 22, 2016 1:40 am

Re: What's wrong with my extruder?

Postby Jetguy » Thu Mar 09, 2017 11:12 pm

did you measure filament diameter? There is no guarantee you don't have a spool that the filament varies in diameter. This system stock will not tolerate oversized filament very well- much over 1.85mm if I remember correctly. If it was smaller and ran fine and got into a thicker section- totally could explain your troubles. Also ABS is prone to sucking moisture right out of the air. That causes it to swell too.

Kingdom3dPrinting
Posts: 8
Joined: Fri Feb 24, 2017 2:19 am

Re: What's wrong with my extruder?

Postby Kingdom3dPrinting » Fri Mar 10, 2017 6:57 am

Thanks again for the response

I checked the filament, it is exactly 1.75mm. I also swapped to a different spool with no change.

The other successful prints measured the same.

My filament is in sealed boxes with cupboard sized dehydrators in each (I have over 50 spools open). You can feel that the air is dry inside when you open them.

If it is definitely not the motor or stepper driver, does that mean its something more sinister on the main board?

In the mean time I will back off the tension on the filament - I still think there has either been a filament path resistance change somewhere or the motor does not have as much torque as before.

Still open to ideas.

Kingdom3dPrinting
Posts: 8
Joined: Fri Feb 24, 2017 2:19 am

Re: What's wrong with my extruder?

Postby Kingdom3dPrinting » Fri Mar 10, 2017 8:35 am

Well you'll never guess what.

Powered it up today and it's working fine :-S

The only change is being powered off for 24 hours and switched on again.

Must have been some random electrical glitch that only reset after a decent amount of time powered down...

It's been printing abs perfectly for 1.5 hours now, when it couldn't even extrude at all before.

I'll post back here if anything changes.


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