Can't figure out extrusion problem

Hi,

I have Prusa i3 kit that I put together 5 months ago. Print quality was always much worse than I see other peoples' pictures, but at least it was consistent. Lately, I've been having a persistent issue with extrusion. Motor will make clicking sounds (skip because it can't push the filament through) and I can't push filament by hand while it's doing that.

I have a knock-off E3D V6 hotend, print PLA, and 0.4mm brass nozzle.

I tried going through different guides and q&a, etc, but to no avail. Here are the things I tried:
- Changing filament: same problem with my black or transparent PLA filament
- Checking feed path: I had suspected that sharp edges at the top of the heat sink might be grabbing the filament, and it prevents it from moving. Sanded them, but still no luck.
- Replacing the nozzle: went through 3 nozzles, same result. Each nozzle I take out, I simply pull PLA out when it's about 90-100C. I'm able to pull 0.35mm piece of wire through the nozzle, no additional cleaning required. (I use these: [smile.amazon.com])
- Replacing heat break: I thought heat break might be a problem. Got a new set, and replaced 2 of them, still no luck (I used these: [smile.amazon.com])
- Increasing temperature: PLA I use starts flowing at around 165. I print at 180. Tried to increase to 190, still same issue.

Any ideas what I can try next, or what part should I buy to make my issues go away?

Thanks!

I tried one drastic thing today: slow down print speed from 50 mm/s to 35mm/s. This seems to have helped quite a bit. Even though I occasionally hear a skip, it is very rare, and usually it's just one skip, and it keeps flowing. This makes some sense, but some holes remain. Like previously when it would start skipping, I'd go for more than 10 seconds with just skipping, until it starts feeding again. Seems like if the problem was with not enough time to melt PLA, I'd not have a single 10-second period of no flow in order to return back to normal and print fine for the next minute. So still looking for more ideas to try.

I had similar problems when still using the old J-heads.
Got better when I realised that not all melting chambers are designed the same way but the real deal was an all metal hotend in the long run.
There are some things I noticed when it comes to these fancy hotends that can allow for screwups.
Firstly the type of nozzle itself - long and pointy or short and quite flat seems to be the only ones on the normal market...
Secondly the heater block and cartridge/heater itself.
Last but not least the thermistor...
Not going into the details of quality in terms of good finnish, no gaps or sharp edges, done that a few times already
Back in the day all hotends where packed with insulation often all the way down to the nozzle.
All-metal-hotends go the opposite way by being naked and adding a fan for cooling.
Now, let's look on how the stuff works together:
The plastic comes down the coldend, goes through the heat break and starts to melt in the melting chamber - at least it should.
To get the correct temperature the thermistor must be placed properly, having somewhere on the outside corner with no insulation around the block usually gives lower readings - in return the real temp inside your nozzle might be too high already.
The heating element must be able to melt the plastic at the highest rated speed, usually done by using 40W or more here.
So not really much you can change to make things better if the stuff is meant to work this way.
Of course doint the screw connections with the proper tension is a must but you already know that...
What you might not know is that the way you screw the nozzle in is important too.
Especially longer nozzles can allow the plastic to cool down before the stuff comes out.
This means when assembling your hotend the nozzle should be screwed in all the way once all is tight.
To do this you go all the way in and then back one turn.
Tighten up the heatbreak by hand and once all is on operating temp you set the nozzle tight.
You don't want to set the nozzle against the heater block! You want to set the nozzle against the heat break to form a proper seal here

But despite all the thing you could check and maybe fix: did you try a different filament?
In too many cases the culprit is a bad batch and before messing with settings that always worked fine or taking it all apart it can pay off to just buy a new roll...

Screwing the nozzle correctly: check (it used to be a problem for me, but I figured it out in time). But this gives me another thought. There is some residue of plastic on the threads (not much) that got there when I didn't have it screwed on properly. Could that be a problem? Seems to me like it can't be that sensitive, as thermal conductivity of brass is very high...

Trying a different filament: check

My conclusion on lower speed seems to have been premature. Even though it looks like it helped a bit, does not seem like it is long term. I had an 8 hour print overnight, and I see top layer is not solid, as it usually is when I have no issues extruding. Although I was not by the printer for the most of the run to witness any extrusion problems.

A bit of remaining plastic on or in the thread is usually not a problem, once hot and you tighten it the stuff will be soft anyway.
That leaves the extruder not pushing filament - did you check the curent for the motor and the extruder can move properly?

I tightened it when hot to prevent plastic bits being a problem.

I checked extruder vref, and it's set correctly. Everything else also looks good, and does not seem like there are issues. And I can't push filament manually when this problem is happening, so don't think it's anything to do with the motor or gear. It's something down from there.

Also, just killed another print, as even with low speed it skipped almost entire layer on a part

Edited 1 time(s). Last edit at 05/05/2016 08:34AM by sergeys.

Just tried pushing filament by hand, with it sitting idle, at normal printing temperature. It is definitely much harder than it used to be when I swapped out nozzle and heat break 2 days ago. Trying to bring print speed even lower now, will see what happens. It's so slow, it's painful to watch

But does this point to bad filament, bad nozzle, heat break, or something else?

Can you post a picture of your extruder and hotend? You said it was a copy of an e3d v6, but the throats you linked to are mk8 style.

Yeah, they do look out of place They are too long for the assembly, so there is ~12mm gap between the top of the heater block, and bottom of heatsink.

I'll post pictures when I get home tonight.

Are they a loose fit? The V6 uses an M7 thread on the top part of the heatbreak, where as the MK8s are M6 throughout.

No, I didn't notice it was loose. I took the original throat, and it's the same thread as the one I have, and it's the same on the top part and bottom.

Here's the pic of the hot end: [drive.google.com]

is your clone have the ptfe tube inside ? some do some dont... both mine have it and I purchased all metal heatbreak when I want to print abs.

I had a similar problem, turn out the thermistor that they use on both my clone were way off specs, when I set the heat to 200C I was getting only 170C I was able to print but really slowly, if I had infill too quick all I got was skip and grinding filament.

My solution was to use a multimeter with a thermocoupler and put the probe inside the nozzle and check the temperature then calibrate the thermistor with a large offset to match the temp I was asking.

So maybe you should start there and make sure your temps are correct.

BTW must clone are M6 not M7 and can use lot of different hotend nozzle,heatbreak because of that, got mine on a mk8 nozzle from china the finish quality inside was 5X the nozzle that came with the clone. Both my clone work fine since I fix my temps problem but I spend some time polishing the heatbreak. Some clone require a little extra work.

Clone did not have PFTE tube. But this throat has PFTE on the heater block side, and nothing on the feed side.

I don't think temperature calibration is the issue, as I did a test: start with 190C, and every 5 mm drop 5C. I was able to go all the way down to 160 to get constant skipping (I presume due to not hot enough to melt). But I'll check the thermistor, maybe it's in poor contact with the block (although it's screwed in, I don't imagine it'd be a problem.

How did you polish the heatbreak? You mean inside?

I switch around my heatbreak with the ptfe inside so its ptfe>metal>block>nozzle I got 2 clone, one with the ptfe close to the heating block and the other had it in the cooling portion, I chose to go bowden all the way to the block and its working nicely the ptfe stop right before the block start, then the plastic melts in the small diameter metal heatbreak portion and that the portion I polish just to make sure the platics wont stick too much to the wall. Also my nozzle is very well polish vs the clone one and have a smaller length at the last orifice (0.4mm) probably help with less pressure.

I polish the heatbreak by first putting the heatbreak on a drill and then use 1500 and 2000 water sandpaper roll in a tiny tube and hit the drill while I push and pull the paper inside, then I use polish compound stick it in the hole and then use a smaller drill bit to turn the compound inside while being careful to not lets it touch the side of the heatbreak ( you dont want to create new drill mark), the best is to find something in platics to do this. Then I lets the heatbreak sit into a jar full of brake cleaner to dissolve the compound, wash it and its done.

Ok, I figured out why it's not extruding... Check out this thermal image of my "hot" end: [drive.google.com] (never mind the misalignment of the thermal and real images)

This is quite different from ones I can find online: [drive.google.com]

That red blob is supposed to be white (it's white on the screen, but for some reason solid red on the picture). But range of the camera is only up to 120C. My heater block is at 180C in the image, while the nozzle stays at a cool 69C. This is crazy. Not sure how this can happen, with brass and aluminum in direct contact, I should be getting much better heat transfer.

I'll try to disassemble tomorrow, see if there is anything on the thread that might impede heat transfer so severely, and reassemble. But even stainless steel throat that is at the top of the heater block is at 81C. This is a mystery. Any ideas?

I don't understand - if the cooler section you've marked is the nozzle, why does the hot area appear to surround it? I can't seem to map the thermal image to the visual you posted earlier.

Some context on how picture was taken: I raised hot end ~80mm, then took a picture looking up from heated bed, about 45 degree angle, looking up. Aluminum heater block is very hot, 180C. While the nozzle itself is only 69C. So the nozzle is much cooler than the block. There is a theory that nozzle does not radiate infrared as aluminum. I'll check tomorrow in different settings, but I'm pretty sure that's not correct.

For such thermal images it really pays off to have a visible overlay.
But the temp difference becomes quite obvious if you consider a few things:
1. The nozzle is quite a long one, it can only get heat from the block above where the thread is.
2. The nozzle is filled with plastic, unless you kept the set temp for a few minutes there is no chance the nozzle reaches a high temperature.
Only if the hot plastic is flowing through the nozzle the temp will even out properly.
3. If the melting chamber goes all the way down to the tip then the nozzle will act like a heat break here as there is only heating in the threaded part.

It also looks like your nozzle is not screwed all the way in.
The heatbreak is of poor quality (my suspicion) as there should be a thinner neck right above the heater block, look extreme long too...
The heatbreak should be as far into the cold end as possible so you get active cooling as close to the heater block as possible.

This particular picture was taken after about 10 minutes at 180C without printing. But the same was true when I checked the picture while it was actively printing. I was making assumptions on how it should look by googling thermal images from other people. And they all have nozzle at the same temp as the heater block, roughly.

I've got another set of heat breaks that are e3d v6 specific. Should get them today, and will see how they work. I may also try some thermal conductive paste on the threads.

Quote
sergeys
Some context on how picture was taken: I raised hot end ~80mm, then took a picture looking up from heated bed, about 45 degree angle, looking up. Aluminum heater block is very hot, 180C. While the nozzle itself is only 69C. So the nozzle is much cooler than the block. There is a theory that nozzle does not radiate infrared as aluminum. I'll check tomorrow in different settings, but I'm pretty sure that's not correct.

Ah, OK, I understand the angle now - thanks. I agree, that seems really odd. From the photo of your hotend I can't tell how far the nozzle is screwed into the heating block. It should be almost all the way in, is that the case? The recommended procedure for fitting the nozzle and heatbreak is to put the nozzle in first, screw it all the way in so that the shoulder is up against the heat block, then back it out a 1/2 turn. Screw the heatbreak in to meet the nozzle, bring up to 200C and then do the final tighten of the nozzle against the heatbreak. If you've already done that then the only thing I can think of is to add some high temperature thermal compound to the threads of the nozzle. Don't add compound to the threads between the heatbreak and the block as you want as little conduction on that side as possible. There's always going to be some amount of thermal gradient down the length of the nozzle, but I'm surprised it's as much as your image shows.

Tried with thermal conductive compound, but not much difference. Raised the temperature by around 10C, but it's still at 79C, which is way too low. I think I need to try a new heater block, one that is not contaminated with PLA from my incorrect setup of nozzle and heat break before (plastic was oozing past the threads)

Yes, I do screw in nozzle correctly. I use the 1/2 turn method described above.

Another point I see is that this nozzle has quite a large piece that's sticking out. One of the other nozzles I used before is only about a 1/3 of the size past the threads. Maybe I'll try that one too, while I'm waiting for a heater block.

Silly question, but you don't have a huge fan blowing directly on the nozzle do you? I can't think of how else the nozzle could get so far below the block temperature, assuming the block temperature is actually around the expected 190 or so. Do you have an M6 tap and die? If you do, you can easily clean out old plastic by running over the threads.

No, I don't have a fan blowing. But yes, indeed: I have a tap kit. That's a great idea. I'll try cleaning it out with that.

Update on things tried... Installed different nozzle, that has a very flat profile (essentially less heat loss), and verified that temperatures are now good. Still no luck, same issues.

Swapped out heat break for the one that came with the hot end, replaced a nozzle with a brand new one. First few layers seemed to be ok, but then started skipping like crazy, digging a cavity in the PLA, and essentially spinning in place after that.

I don't know where to go next, but a completely brand new hot end

If the drive gear chews a section out of the filament then the solution is usually more tension on the idler.

About a year ago I had the same problem, after checking everything possible I end up trying a new stepper driver, that fixed the problem.

Have you changed the heater block ?
If the hole for the heat break doesn't align with the hole for the nozzle you will have problems getting the filament into the nozzle and so struggle to heat the filament. This is compounded by the smaller crossection so it doesn't flow well.

I haven't changed the heater block (just because I don't have one extra around). But I have gone through the threads with an M6 tap to clean out all plastic.

I'm buying all these part sets one by one, keep spending $10 on each set. Might as well just get a full e3d lite6 kit, and hope that'd be of a great quality. Any good suggestions to sources of good quality 3d printer parts? Amazon seems to be hit or miss, and it's a pain to figure out with so many parts that need to work well together in sync.

I'll try new stepper driver. I have a spare, and see how it works.

Swapped stepper driver, no change. Swapped filament again... And looks like it's printing normally now. Can't believe it, as previously swap didn't help... Maybe this time something aligned, so hope this is going to stay!