Extruder printing in air with non-Raise3D PLA

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jon_bondy
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Extruder printing in air with non-Raise3D PLA

Postby jon_bondy » Tue Feb 13, 2018 9:05 pm

I have made a series of prints with Raise3D PLA and most of them have come out pretty well.

I just switched to some Ultimachine clear PLA, and am having problems. Loading is fine, and the print starts out OK, but after a while, the extruder is printing in air. The filament has failed to feed properly. If I Unload, cut off a foot of filament, and then Load, all is well. But the next print fails in the same way. During the Load operation, I can extrude 2 feet of filament without a problem. I was printing at 205, but have increased to 215 (I print at 200 on my other printers). That did not help. I freed up a loop of filament to reduce drag for the extruder. That did not help.

Any suggestions?

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Vicky@Raise3D
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Re: Extruder printing in air with non-Raise3D PLA

Postby Vicky@Raise3D » Wed Feb 14, 2018 2:15 pm

After you find air-printing, do not stop the print immediately. Try hand push the filament to check whether the feeding can continue or not.

Jetguy
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Re: Extruder printing in air with non-Raise3D PLA

Postby Jetguy » Wed Feb 14, 2018 2:45 pm

If your extruder stops extruding, the first thing you the owner, user, and troubleshooter of the printer has to know is," did it skip or did it slip"?
Slipping, AKA grinding the filament is caused by failure of the user to properly adjust the pinch distance between the drive gear on the motor and the V -grooved bearing that presses the filament against the drive gear. This is accomplished by loosening the 4 screws holding the motor to the extruder feeder aluminum body. You then move the motor and thus gear nearer to the V-groove bearing and then tighten the 4 screws.
The reason here is different filament may have a different diameter and because this is a fixed distance system, you have to make an adjustment or else the drive gear can slip and grind a divot into the filament. Slipping/grinding is the more common error. This is obvious by filament dust being stuck in the teeth of the gear, a divot in the side of the filament, and evidence of a lot of ground filament under the clear acrylic feeder section cover.

That said, you can go too tight and in this case, too tight causes a lot of friction because the drive gear is deforming and mashing the filament. This means the motor force is split between mashing the filament and pushing it into the nozzle. In this case, the filament grips and does not slip, but the extra force causes the motor to skip steps (a clicking, thumping, or tapping sound).

You have to find the balance. You never ever want to slip, but at the same time, not so tight you are losing motor force and thus getting less drive force into the filament pushing into the nozzle. In the past, there was also the shim method where a shim is placed between one side of the motor and the feeder block and that causes the motor to be angled and the shaft then amplifies this adjustment to squeeze the filament against the drive gear from the fixed position of the V-groove bearing.

Adjustment and shims talked about here viewtopic.php?f=2&t=879&p=8367&hilit=paper+shim#p8342

In this thread, I highlight a cheap but good upgrade drive gear that can and does improve this grip and reduces the friction over the stock feeder gear. Again, cheap way to improve the printer and simple viewtopic.php?f=4&t=6193#p24902
Last edited by Jetguy on Wed Feb 14, 2018 3:13 pm, edited 1 time in total.

Jetguy
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Location: In a van, down by the river

Re: Extruder printing in air with non-Raise3D PLA

Postby Jetguy » Wed Feb 14, 2018 2:52 pm

Here is why I said all that.

I do not know 100% the root cause of why you stopped extruding mid print. We simply do not have enough details from your post to make that kind of verification. What we do know is that you stopped feeding, and that ONLY with a manual intervention of unloading the filament, cutting off the damaged end (more evidence that it likely was slipping and grinding) and that it was not a hard nozzle clog because you could load and feed fresh cut untouched filament.

Which goes back to why you can never, ever slip and grind. If it slips and grind in this system, then a divot is formed. Since this is a fixed distance idler style extruder, if the filament is not pressed into the drive gear hard enough, it slips and grinds. Like a car stuck in the mud it digs a hole. It cannot ever get out of the "hole" on it's own. So if it slips, it's a self amplifying error that a tiny slip becomes a big slip and a big slip grinds and then it's GAME OVER for that print.

If you get a blockage and the grip is good enough that it never slips, the motor is STILL trying to turn and when the clog melts or pressure drops in the nozzle, then the feeder will self correct and start feeding. Now obviously you don't want jams and stops and skips because that's missing plastic that should be in your print. However, given the choice, you would rather skip steps than slip and grind.

Jetguy
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Location: In a van, down by the river

Re: Extruder printing in air with non-Raise3D PLA

Postby Jetguy » Wed Feb 14, 2018 3:00 pm

Other questions:
How hot to the touch was the extruder motor on the feeder at the time of jam? Too hot to touch? Uncomfortably warm, or warm but not hot?
Were you printing PLA with the top cover (lid) installed?
What is your ambient temp in the room around the printer?

The reason for these questions, PLA softens (does not melt, but softens) at relatively lower temps. Clear PLA has almost no additives and is even MORE prone to this. If the filament gets soft in the feeder section before the actual hotend melting and nozzle it can and will jam and stop extruding.

So you need to solve the first set of things I mentioned related to adjustments and grip, but also pay attention to temp around the extruder feeder section with low temp materials like PLA.

jon_bondy
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Re: Extruder printing in air with non-Raise3D PLA

Postby jon_bondy » Wed Feb 14, 2018 11:41 pm

Thanks for your help!

I hope that the attachments appear as pictures. They are in the attachments file list, but I also saw an HTTP Error.

The pictures show the filament where it stopped feeding. While the gear marks are different at the very end, there are no obvious divots, and there is no filament dust or ground filament under the clear extruder cover.

Both the Raise3D red PLA filament and the UltiMachine clear PLA filament are exactly 1.75 mm in diameter, so changes in filament diameter would not explain the difference.

When the print fails, there is a click about every second or so. When I try to push the filament in further, it does not help/work. The bottom stepper motor is hot (about 41 C) but not too hot to hold onto. The top stepper motor is only a bit cooler at 34 C.

I print PLA with the front door open and the lid propped open 6" at the front. Room temperature is 75-80 F. Previous prints were printed with the lid removed (I just printed the device to hold the lid up). I tried it again with the lid off, but it failed fairly quickly, in the same way. I tried again, this time with Raise3D red PLA with the lid propped open and it ran to completion. So, lid position is not the issue.

I am using the extra guide/Bowden tubes that run from just above the filament reels to the top of the extruder. If this is a bad idea, I can remove them, but the Raise3D red PLA printed a 10 hour job without a problem, so I doubt that these tubes are the issue.

The only variable is the filament, and that is causing the failure. Perhaps I should be printing it hotter or colder. I can use the UltiMachine filament on the CR-10 (which does just fine with it).

jon_bondy
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Joined: Fri Jan 26, 2018 6:24 pm

Re: Extruder printing in air with non-Raise3D PLA

Postby jon_bondy » Thu Feb 15, 2018 2:48 pm

Out of curiosity, I tried PolyCarbonate (since I'm looking for something clear) and that works fine. It is less clear [sic] whether I can find a soluble support structure to use with PC.

jon_bondy
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Re: Extruder printing in air with non-Raise3D PLA

Postby jon_bondy » Thu Feb 22, 2018 2:44 am

Julia Truchsess had this to say:

"The clicking problem you describe is typical of all-metal extruders with some PLAs. The PLA gets warm in the feed tube, turns to jelly, and can’t be pushed. For some odd reason in my experience it seems to happen more with “premium” varieties of PLA, and yes, probably transparent. I have some Taulman clear PLA that I just can’t print. You might want to check out T-Glase – it’s got a nice finish. Never tried it on the Raise, and wasn’t highly successful with it on the Zortrax either. I used Taulman “Blu-Print” for a backlit item once and it looked really great, and that stuff is easy to print."


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