Can't get PLA to print 🙁  

RE: Can't get PLA to print 🙁

Installed the new temp sensor but it made no difference.

Re-flashed the firmware and downloaded prusa slicer and installed it again, sliced the same model, checked all connections, checked the hot end again, checked the bondtech gears again, tried different idler tensions, still no change, I can push the filament through by hand it feels quite smooth and free.

Out of ideas to try now.

RE: Can't get PLA to print 🙁

Printing is pretty simple in its basic form. Heat the filament until it melts: push it through a smaller nozzle.

There is a reason there is a extrusion multiplier setting.  Measure your filament and do a test cube, change the diameter and multiplier as needed. 

There are also things to change in the base code - defines that work 99.9% of the time, but can be changed to meet special needs by pushing them with gcode commands and saving them back to EEPROM. 

The last thing I can think of is the Bondtech gears aren't aligned with the filament path - and this allows slippage. Or that you have something dragging on the filament keeping faster extrusions to fail like a poor fitting filament sensor ball.

And it could be as simple as an extruder motor not making the torque it needs. Either a resistive wire, bad driver, weak fuse, etc.

Several of the filament friction issues should cause clicking - the teeth jumping over the filament and associated debris and dust and ground up filament sections. The gear misalignment should also show symptoms - lopsided or no teeth marks in the filament. The motor torque may not have symptoms - running in normal mode, checking for E crashes may indicate something. 

And - as I said in the other thread. When out of ideas, time to call the professionals over at Prusa. There's only so much head banging that a person can call "educational".

RE: Can't get PLA to print 🙁

@tim-2

I did the test cube a couple times the other day, and adjusted the extrusion multiplier to what I thought was correct, when reloading the pla it was then really over extruding, tried to print again and under extruding.

The Bondtech gears look ok, I can do a photo of them? I've tried moving the one of the motor shaft slightly, and making sure it's tight.

I reloaded the pla about 3 hours ago, did a perfect looking 50x50x3mm print, let it cool and it's gone back to having gaps again.

Maybe there is a main board fault like you say, thank you taking the time to reply, and thanks to the other people who replied, hopefully Prusa can help me solve this one.

RE: Can't get PLA to print 🙁

@mattj

Early on I looked at your cold pulls, and the tooth marks seemed to be okay - so that's probably not this issue.

I sometimes wonder if we don't get too critical of the print.  There are times, even when printing tests for these threads, where I saw infill not lay down perfectly and had gaps. I think I should chase it and when the print is done I move on to other things and forget what I saw.  The filament we use isn't perfect, and I do not believe the specmanship of the companies proclaiming 0.02 mm diameter accuracy. Even getting a tool to measure a diameter that accurate is problematic. And some filament I've used - even Prusament - has read under 1.7 mm diameter on my trusty mechanical dial gauge ($150 in 1975). 1.70/1.75 is a larger deviation than the 0.02 Prusa warrants - by a lot. Still only 3%, but maybe enough for some of these odd effects seen from time to time.

But even that sort of variation doesn't quite explain every print, or every other print like these two threads. 

Here's to hoping Prusa can provide an answer.

RE: Can't get PLA to print 🙁

ps: as a wild and crazy idea - can you get to and remove that filament sensor ball? I seriously doubt that's an issue ... but heck, it's a mechanical trap waiting to happen.

RE: Can't get PLA to print 🙁

@mattj

Have you figured you case out?

I've been through 12 hours of chats with support and no luck so far.

RE: Can't get PLA to print 🙁

@doctorshtein

Hi,

Still no solution, I also did a live chat yesterday for about 6 hours, rebuilt the V6, reset and re-flashed, updated to the new firmware.

Do you have a thermocouple meter like K-type probe? if you do we could compare nozzle temps at the tip

I think the temp is being read incorrectly, I could be wrong but I need to rule it out completely. There is another socket on the board, I think the temp sensor is in T2 and it can be moved to T1 with a slight firmware edit.

RE: Can't get PLA to print 🙁

@mattj

I have been following this thread.  It obviously is not the thermistor.  I wonder if you have a bad board.  

RE: Can't get PLA to print 🙁

I am running the latest firmware now and just tested again with the temp probe, and the nozzle temp reading on the probe meter matches exactly the reading on the printer screen, image below shows where I tested it, also a tiny bit of thermal paste on the probe ball, set nozzle to 210c and reading on the meter was 210c, same at 225c etc...

I need to do some more printing today and see how it goes, ran out of time last night.

RE: Can't get PLA to print 🙁

Forgot to mention in the the above test was without moving the sensor to T1, I have not changed it. 

fully reset, and installed new firmware version, did wizard and PID cal

RE: Can't get PLA to print 🙁

After doing more prints today, the above did not fix the problem, it is still exactly the same as before.

RE: Can't get PLA to print 🙁

There's really nothing on the board that would cause this type of issue.  Even a bad ADC in the uC would have been found in these tests. 

It is down to HEAT vs PRESSURE ...

In yet a third underextrude problem on a new Mk3S+ printer, his problem is looking exactly like the heat break issue from earlier on.  This experiment will seem weird, but try it and carefully look at results - any change means something.

Reduce your print temp 10c --- does the underextrusion change in any way (as in, does it get better)?

.

RE: Can't get PLA to print 🙁

Oh- and a second test: try increasing print speed in a second test: to 125%. So you'll see 125% in the display while printing, not the 100% normally showing.  Both of these tricks seem to be effective at reducing heat break jams.

RE: Can't get PLA to print 🙁

@tim-2

Then obviously, I do not understand the problem.  

RE: Can't get PLA to print 🙁

@cwbullet

Some people refuse to acknowledge the heat break can cause jams. It can, it does. The use case is specific, but when parameters add up, the act of pushing and pulling on solid filament that is connected hydraulically to a pool of molten material can extrude some of the molten material up the filament path, where it rises and cools, and solidifies. The Prusa heat break has a step near the hot zone where if filament reaches it, the now solid flow locks in place. Unloading is still possible, but forward extrusion becomes impossible. 

Here is a photo of polycarbonate that shows the backflow - the shell that fell off after unloading - along with the 2.2 mm diameter at the tip.

Here's a photo of a tip that shows the entire profile inside the heat break and nozzle ... you can measure each diameter down the path.

Some people try to blame heat creep ... but that isn't the mechanism. The heat break is working normally, and isn't too warm from above, the filament isn't deforming prior to the hot zone, etc. 

Here is the profile of the Prusa heat break showing the step that is the problem: that little step just at the lower neck of the heat break. If it is not at melt temperatures, the heat break will be subject to jams when printing. 

RE: Can't get PLA to print 🙁

@tim-2

I have to agree.  It can do it.  

RE: Can't get PLA to print 🙁

Still no resolution to my problem, Prusa sent me another new temp sensor and new extruder motor, seemed ok for about 4 prints which look decent, now back to the same under extruding again

RE: Can't get PLA to print 🙁

@mattj

This has to be something with the assembly or heatbreak.  

RE: Can't get PLA to print 🙁

@cwbullet

I am not sure what to do with it, I have put the original prusa heatbreak back in, I've had it all apart about 20 times or more, I've not looked at it or used it for a few days now, just left to one side

RE: Can't get PLA to print 🙁

@mattj

If you are frustrated, that is best.  It will work.  Have you thought about replacing the nozzle and heatbreak?