Extruder skipping, sparse print

Post Reply
evanr
Posts: 101
Joined: Thu Nov 29, 2012 3:09 am

Extruder skipping, sparse print

Post by evanr »

Hi All,

I've been printing with no problems (with the same filament) until now. All of the sudden a 7hr print got ruined after 6hrs.

Now, when I print the first 10min is perfect, then the extruder motor starts to skip more and more over 20min and the print turns out fluffy. Then I have to cancel the print.

Here are some stats:
material: PLA transparent
material temp: 205
bed temp: 65
Felix 1.5 with new 2.0 extruder parts
HotEnd V4.0

I turned the pot dial to the right, the extruder motor just clicks more, if to the left the motor relaxes but doesn't extrude as much.

Seems to extrude nicely from idle, so I print then it gets fluffy.

Some things I may consider:
- dust in the extruder (so I will try to clean asap)
- hotend fan is currently standard 5v as per assembly instructions. Would switching to 12v to create more airflow help? How do I do this?

thanks,
Evan

andrewsi
Posts: 130
Joined: Mon Dec 23, 2013 1:26 am

Post by andrewsi »

Extruder Skipping occurs because (for any of several possible reasons) the filament is not getting hot enough, or there is resistance to pulling it through in the first place (tension upstream of the extruder). You list a couple of key points: your temp's already up at 205, and it starts to get fluffy after the print is already several minutes in, so my guess is that you're trying to print too quickly after the first layer, perhaps.

You can try raising the temp a bit more to maybe 210 or 215 to make the filament even gooier, but also likely to help would be to slow down the overall print speed - you didn't specify what your average print speeds are in your slicer settings. Are you going much higher than 60mm/sec? When you print faster, the filament doesn't have as much time to absorb heat from the extruder and may not be fully melted as it pushes through, which leads to additional resistance. Slower print speeds don't pull the heat from the extruder as quickly and it gets more of a chance to fully liquify (and to push less volume per unit time).

As for the fan, higher fan speeds isn't the answer here, if anything, that only helps cool the head more.
__________________________________________
Andy Silverman, Technogeek in Seattle
Felix Tec4 Single-head

evanr
Posts: 101
Joined: Thu Nov 29, 2012 3:09 am

Post by evanr »

thanks andrewsi.

feedrate = 100
flowrate = 100

I have always printed at these settings with no problem.

... just cleaned out the extruder head, used .35mm drill bit, soaked in acetone and flushed out.

Same problem still happens at about 5 - 10min in.

It all started with the 7hr print, then fluffy at 6hrs.
Otherwise the first 6hrs were perfect, then the extruder ocassionally hick-uped which became more frequent.

First time printing something 4" diameter x 2"H.... don't think that matter though.

When it gets fluffy, less filament is being pushed out and I notice that the bearing is not moving but the motor is.

If I pause print, lower the bed and do a test extrude, not much is coming out. If I push the filament from the top and force it through it will continue on its own. The bearing moves again.

I have tried 205 and 210, same problem.

There is clearance between bearing and extruder head (filament entrance), good. Extruder wheel looks good, no slippage.

What else would cause a backup?

I remember reading somewhere on the forum that increasing the power to the HotEnd Fan (not airduct fan) would help keep the filament cool before it reaches the insulator/end. Preventing backing up.

andrewsi
Posts: 130
Joined: Mon Dec 23, 2013 1:26 am

Post by andrewsi »

It's certainly true that you don't want the filament to start to liquefy too high up in the head, but I'm not convinced yet that that's the problem.

Also, feedrate/flowrate of 100%/100% is relative to the speed of movement specified in the Gcode file that your slicer produces. You have to look in the slicer settings to see what sort of mm/sec it is moving the print head at during extrusion. Slower movement rates are usually associated with "higher quality" settings.

The extrusion rate is calculated indirectly as a function of the layer height, nozzle width, and desired extrusion width, with the goal being a fixed volume of filament is extruded per unit length, regardless of how fast the head covers that distance. Moving faster, and therefore extruding faster, requires that the filament get heated up from room temp to the gooey state more quickly and if the heater can't keep up, that can lead to additional pressure and extruder skipping.

I would suggest experimenting with both slightly higher extruder temps, and slightly slower print speeds in your slicer settings. Skipping usually means the tension is fine: it's pushing harder on the filament than can be extruded. Head clogs are certainly a possibility too, but in my experience a lot seems to get blamed on "clogged heads" that really isn't anything of the sort. Does a different color or spool of filament produce the same problems with the same settings? I've found that the required temps and speeds can from brand to brand and particularly color to color.
__________________________________________
Andy Silverman, Technogeek in Seattle
Felix Tec4 Single-head

evanr
Posts: 101
Joined: Thu Nov 29, 2012 3:09 am

Post by evanr »

ok thanks,

Travel Feed Rate: 4800mm/min
Z-Axis Feed Rate: 600mm/min
Is this it?

"slightly higher extruder temps, and slightly slower print speeds in your slicer settings." andrewsi

... will try a higher temp and slower print
... will try a different colour

BTW, what are the standard slicer settings & where do I adjust this?

andrewsi
Posts: 130
Joined: Mon Dec 23, 2013 1:26 am

Post by andrewsi »

That depends on what software you're using to import STLs and print them. Repetier Host? Something else?
__________________________________________
Andy Silverman, Technogeek in Seattle
Felix Tec4 Single-head

evanr
Posts: 101
Joined: Thu Nov 29, 2012 3:09 am

Post by evanr »

I slice with SFACT

Just did the following, same problem for all:
- 215temp/feed100-flow100
- 215temp/feed90-flow90
- recalibrated the bed, thinking the tip was too close causing a backup
- tried a different colour, both filaments are 1.74mm Makerbot

Same problem, after about 5 - 10min the extruder motor starts to hickup.

regular test extrude @ speed 80mm/min, no problem

Could the extruder motor be fried?

Any other ideas?

evanr
Posts: 101
Joined: Thu Nov 29, 2012 3:09 am

Post by evanr »

Repetier Host V0.82b
SFACT slicer

evanr
Posts: 101
Joined: Thu Nov 29, 2012 3:09 am

Post by evanr »

Test extrude during a paused print right after the extruder motor starts to hick-up, problem continues with hick-ups.

Test extrude after kill print and stop motors, extrudes ok with no hick-ups.

andrewsi
Posts: 130
Joined: Mon Dec 23, 2013 1:26 am

Post by andrewsi »

Well, those are EXTREMELY old. Most everyone has moved away from SFACT to newer/faster slicers such as CuraEngine, Slic3r, or KISSlicer. If you update your version of Repetier Host from their website, it'll come with a customized version of CuraEngine built in.

You might consider just reslicing with the newer software (which will be much easier and friendlier to configure than SFACT ever was) and see whether you get a different result.

The only thing I could think of being wrong with your motor would be an intermittent connection to one of the poles that only shows up if it gets warm, but that seems unlikely to me given that the X axis motion probably puts far more mechanical stress on the wires than any change in temperature.

On the off chance that this is what you suspected and the temp is too high, and eventually backing its way up the extruder, have you tried lowering print temps to 195-200? If there's a genuine clog it would be much more noticeable at the lower temp, i.e. it should start skipping much sooner.

The other random thought that comes to mind is an inaccurate thermistor in the head. I went through several of the "official" metal-encased thermistors from Felix and they went bad very quickly: They're embedded in some kind of very rigid epoxy inside the metal shell and I suspect that they were cracking internally or something. I built my own with some 3mm hollow brass tubing and flexible RTV high-temp silicone gasket material around an equivalent thermistor about a year ago, and haven't seen a failure since. I bring this up because temps were very unstable on the Repetier graph when the thermistors started going bad, and perhaps weren't reading accurately at that point, so who knows what temp it was actually running at?

At this point I think you could do a few more experiments with temp to see whether the results are different, and with slicer settings (to alter print speed and/or temp), before you consider changing out thermistors.
__________________________________________
Andy Silverman, Technogeek in Seattle
Felix Tec4 Single-head

Post Reply