Backpressure Issue

[mhackney]

But a clogged nozzle does not explain your "first try" that seemed to be jammed with no nozzle installed. How would that be explained?

[javiercordero20]

Nozzles can be defective or clogged with debris. Can you check with the nozzle installed again now?

Hello,

So I reattached the 0.5mm Nozzle and pushed filament manually through the bowden tube out the nozzle. It requires a good amount of force. As a comparison I replaced the nozzle with a 0.4mm Nozzle and noted that it required about the same amount of force to push the filament through.

Its hard to describe force in text so let me explain it like this...

If I grab the filament 5cm away from the end of the bowden tube and push. it will bend due to the force I need to apply to get it to push out the nozzle. So I constantly grab a short 1-3cm away from the end of the tube and push as best I can.

Sincerely,
J.D. Cordero

[javiercordero20]

But a clogged nozzle does not explain your "first try" that seemed to be jammed with no nozzle installed. How would that be explained?

Hello,

I suspect that there was a small clog of filament somewhere that got unclogged when I was flushing the nozzleless hotend with filament.

Sincerely,
J.D. Cordero

[mhackney]

So two different nozzles feel about the same. It does take a some/significant force to push filament and your description is about what I would expect. It seems that this is not the problem.

[mhackney]

There could've been a small piece of debris in the filament or maybe a little shard of metal from the hot end or extruder. I've found a few weird things in filament.

[javiercordero20]

There could've been a small piece of debris in the filament or maybe a little shard of metal from the hot end or extruder. I've found a few weird things in filament.

Hello,

I can switch out the filament but I don't have any other regular PLA. I have:

PETG
CF-PETG
GLow in the dark PLA

I have printed a lot with PETG.

[mhackney]

I don't recommend switching filament.

[javiercordero20]

I don't recommend switching filament.

Alright.

[javiercordero20]

I don't recommend switching filament.

I am now doing the 100mm Extrusion test.

@250C I can extrude 100mm without skipping. (I am aware 250C is extremely hot. no PLA should be that hot. But it was where I started)
@200C it skips. it does not extrude the 100mm cleanly.

I did the same test with a second extruder assembly and I still cannot extrude 100mm @200C without skips.

Let me know what you think.

[mhackney]

I think you are all over the map. What would possess you to run PLA at 250°C??? We had things working perfectly on Saturday and then you immediately changed everything and failed. Slow down, go back to basics. I am sure you still have not read the post I've asked you t read multiple times. I'm out of patience to help any longer, sorry about that.

[javiercordero20]

I think you are all over the map. What would possess you to run PLA at 250°C??? We had things working perfectly on Saturday and then you immediately changed everything and failed. Slow down, go back to basics. I am sure you still have not read the post I've asked you t read multiple times. I'm out of patience to help any longer, sorry about that.

Roger That.

[mhackney]

Slow down, be consistent and work through everything carefully. Others will jump in to help and I will as well but you've got to get on the right track asap! I still suspect an issue with inserting the Bowden in the hot end. Something you are doing or did in the build is not quite right.

[javiercordero20]

Slow down, be consistent and work through everything carefully. Others will jump in to help and I will as well but you've got to get on the right track asap! I still suspect an issue with inserting the Bowden in the hot end. Something you are doing or did in the build is not quite right.

Hello,

First off. I have read your post. the long one.

Second. When I did the extrusion @ 250C I had a hunch which was right. Yesterday night I was talking to a friend who said "what if the nozzle is not as hot as the heaterblock says it is." That got me thinking so I played with temperature to find a sweet spot where it would extrude without skipping(which for me was 220C) . Last night I printed two cubes and now I am printing a bandaid again. No skips so far. So I think the hunch was right.

Here are the print results so far:

For the cube on the right I adjusted the "Slow Down if Layer Print Time is Below XX" In that cube you can see vertical lines down the print. Which as you stated in another post is a limitation of the Rambo board controlling the steppers. Getting to that point is a good sign in my opinion.

For now I am going to do a bunch of test prints to see if the problem is permanently solved. The test cubes I have printed so far look good except for the bottom 2-3 layers. Which I suspect have to do with print speed since those layers are the only ones not printed at the same speed as the rest of the cube. but its a hunch.. for now I am testing to see if the skipping is gone for good.

[mhackney]

Do you have a way to directly measure the temperature of the nozzle tip? There are several factors why the temps might not be correct. However, if you built the machine as described in the assembly guide and flashed with unmodified firmware then temps should be pretty spot on. The things that can lead to problems include:

firmware - changing the thermistor type and recompiling and uploading the firmware. You can check this in Configuration.h
electrical - there is some possibility the RAMBo has a problem or that the thermistor is incorrectly spec'd or defective
mechanical - the cartridge heater may not be installed properly (tightly) or the thermistor is not installed properly (not contacting the heat block or loose) or bad crimp connections to the thermistor or poor thermistor solder joints on the PCB.

Of these, the last one might explain the inconsistent results you've had the last few days where it printed great on Saturday (after we lowered the insanely high retract speed) then you started having problems again - but since you changed slicers, controllers and other things in a constant flux, these changes obfuscated the root issue.

At 250°C I would expect the PLA to run like maple syrup and smell like popcorn. Is that what you saw and smelled? If not, you may be on to the root issue.

[stough]

I've had similar issues with my printer and had to print super-duper slow to get consistent results and, at 50% speed, still needed to print my PLA at 218C to get it to flow without the extruder skipping.

I'm suspecting a couple of possibilities that I'm working on eliminating. First, I think that I may have the nozzle size set incorrectly (easy enough to test). Second is this question of correct temperature readings. I've ordered an IR thermometer from Amazon (just $13.88) to check the hot end temperature. It is only accurate to +/- 2C, but that should tell me if there is anything seriously wrong.

Also, I haven't tried the extrusion speed test will give that a spin today.

My major breakthrough in calibration was slowing down the print (to 50% speed using the LCD interface) and then pausing and restarting after adjusting endstops. As well as watching and listening to a very large slow print (I printed a ring that skirted within just 2cm of the edge of the print area).

Good luck!

Cheers,
Tim

[morgandc]

I have an IR thermo and it doesn't appear to help.... The tip external temp is totally different than the thermistor internal temp.

[IMBoring25]

The hot end is too small and too shiny for accurate IR temperature measurement. You really need a thermocouple.

[morgandc]

Any reasonably priced thermocouple you can recommend? Can you recommend a method for measuring?

[Xenocrates]

Any reasonably priced thermocouple you can recommend? Can you recommend a method for measuring?

Try the local hardware store. They often will have a multimeter w/ thermocouple pack available, and unless you already have a few multimeters, you can always use them.

[Polygonhell]

I own more multimeters than anyone can reasonably justify, so I bought a standalone unit, I think I paid $16 for mine from ebay, amazon has similar models.
For the accuracy you care about, manufacturers don't really matter, you just want to make sure it'll measure the temperature range you care about.
Having 2 probes and the ability to measure temperature differences is a nice to have if you actually want to calibrate the thermocouple, but for measuring hotend temperature you don't need that.

I usually measure the hotend temperature at the interface between the heater block and the nozzle, if you want to make it easy you can unscrew the nozzle slightly and trap the thermocouple in there while checking. But I usually just hold it in place, you need to ensure you have a good contact for long enough for the thermocouple reading to stabilize, obviously it's hot so be careful if you do what I do.

[RocketMagnet]

Don't want to complicate the issue but i'd try the following:

1. Print slow and try upping the temperature a bit but not 250 that's way way too high for PLA.. even too high for ABS IMO (essentially give the plastic time to melt in the hot end).
2. Double check your filament diameter... if it's much thicker diameter than expected your essentially trying push material through too fast and it causes backpressure. Really it's mass flow rate your interested in fundamentally hence why consistent filament diameter/density is really important.
3. If your running repetier software and not Matter control I'd check the temp trace log to see how well it's holding target temp. Clearly lots of things can cause it to vary such as poor PID control or varying filament diameter.. but a temp trace will certainly highlight these as issues.
4. Check you have the correct power setting applied in the Firmware code for your extruder.. I was fiddling a long time ago and reflashed the firmware and set the extruder motor power too low (trying to keep it cooler) and it caused feed issues so I had to raise it back up.

Pretty sure 4 will be covered in the build manual, you'll need to check and mod the code and reflash this back to the board.
I've got a post somewhere on here on exactly what settings I changed and to what.. edit.. its here http://forum.seemecnc.com/viewtopic.php?f=60&t=7239

Some talk about incorrect nozzle temps and this can be due to setting the thermistor type incorrectly in the software but if your bed and nozzle are close at room temp your probably not far off. I ran into this issue when I made a new wiring harness and hotend with a different type of thermistor and had to change it's "type" in the code.


Summary

1. Varying Filament diameter hence varying mass flow. I've had this issue.
2. Extruder Stepper Motor power settings in the firmware (too low). I've had this issue and if I was a betting man... well i'd put an each way on this one

Anyway hope that's helped & not confused the issue more.. there are just so many variables but when you realise it's just mass flow Vs Temp it makes it easier to trouble shoot feed issues IMO.

[stough]

This may or may not help if you have a different root cause, but this solved the backpressure issue for me.

Root Cause: My Bowden tube was not fully inserted into the hot end and plastic was melting above the heat break.

1) You need to clear that plug above the heat break: Get the nozzle to flow plastic. Allow the nozzle to cool below 80c; Release the retaining clip (lobster claw) and push in the retaining ring on the hot end; Set hot end to preheat 100C; With firm pressure, pull on the Bowden tube until it comes out of the hot end. This should "pull out" the plug and some plastic from within the nozzle. If you have a plug of plastic that is bigger that the ID of your tube at the end of the filament, this was probably the cause of your woes.

2) Reinstall the tube correctly. Trim the plug from your filament and hand retract the filament back into the tube about a 1-cm; Allow the hot end to cool; Reinsert the tube into the hot end fully and lock the retaining clip; Now, the special sauce (thanks to mhackney's instruction from a different thread), firmly grip the hot end and the Bowden tube and push them together (the retaining mechanism can slip in this direction) and you may feel the tube seat deeper into the hot end (it felt like I got almost 1mm more).

For me, after that, plastic flows great at 210C. No issue with the extruder stepper slipping or bouncing. I am now able to print at the default speeds (up to 40mm/s) with no problems.

Good luck!
-Tim

[mhackney]

Also it doesn't hurt to make sure the cog in the EZRStruder is aligned properly as per the installation guide - use a short piece of filament to do this as instructed.

A trick for the hotend end of the Bowden is to taper it slightly with a pencil sharpener or even a sharp hobby knife. This helps guide it all the way in. But don't overdo the taper.

[javiercordero20]

Hello,

Just wanted to say this issue is closed and therefore this thread has ended. Backpressure issue was retraction speed and/or length.

[mhackney]

Thanks for the follow up Javier.