First attempt to feed filament - Jammed Nozzle

[wonderemporium]

So I finally got our Rostock Max built and dialed in but ran into a show stopper on my first attempt to extrude ABS before the first test print. It fed up to the tip but then seemed to feed with almost nothing coming out of the tip. I got just a small coil that slowly oozed out of the tip. I was using silver ABS and the little bit that came out looked burned. I did the auto setup for the temp and had it at 260 for the first test extrusion according to the manual.

One thing that may be strange, although I can't tell for sure, is that I had ordered a 0.011" tip and an Onyx bed from the website. This was separate from my Rostock Max which I got through the Indiegogo campaign. Everything came at the same time and the 0.011 tip was not in the box with the Onyx so I'm wondering if it was the tip that was packed with the Max. There was only the one tip so I'm wondering if it was put in there instead of the normal larger tip. It seemed to take an extreme amount of pressure to push the filament through the tip. In the end I had to shut it down and pull the ABS out but now there is a chunk stuck in the tip. I'm going to try soaking it in Acetone over night to see if I can get it out.

One question is, if this is the smaller than normal tip and I had my settings as per the manual which is for the 0.5 mm tip, would it pile up, melt in the tube and jam like this? I don't have any way to accurately measure the hole in the tip to tell for sure which one I have but I may need to order a standard one in the morning so I can be sure what I'm dealing with.

Next question, if I do have the 0.011" tip, will that even work for ABS and if so, does anyone have a clue on what settings to use with it?

[wonderemporium]

Update, I soaked the tip in acetone overnight and was able to get it clean this morning. I found a 0.5mm wire and pushed it through the hole so I do have the correct size tip. I'm about to try extruding again but I can't figure out what else would cause the material to pile up and melt in the teflon liner without much coming through the tip. I will try a lower temp of 230c which seems to be the normal print temp and maybe a lower extrusion speed. The settings were 100mm/min at 260c as per Gene's manual.

I have to wonder if my hotend temp is accurate. I did the auto tune procedure but I don't have a thermocouple for my meter so I'm not sure of any other way to get a good reading on it. Would the abs looking scorched be normal or could I be running too hot?

If the hotend is too hot, will the abs flow more readily or will it burn and jam?

[Polygonhell]

ABS doesn't usually jam in the same way PLA does.
It generally gets more fluid the hotter it gets, but it will burn if it's kept at too high a temperature, and that can block the nozzle.
260 is a bit high because the PTFE liner will deform at temperatures in that range, having said that although I find the thermister is accurate, I find that I need a higher temperature using the seemecnc Hotend than others I have for the same plastic.

Take the Bowden tube off the Hotend, set the temperature to 240 and try and push the filament through by hand, on my machine at that temperature, there is more resistance tan I would expect, but it will extrude. If you can't push it by hand increase the temperature in 5 degree increments until you can.

FWIW I don't have a 0.011in hot end, but given the back pressure I get from the 0.02in Hotend I think you'll find it impossible to extrude 1.75mm ABS though it without it buckling in the extruder body before it enters the Bowden tube.

[geneb]

Well I feel like an idiot. I have no idea why I specified 260 degrees for the hot end in those directions. I've changed it to 245, which is what I've run the stretchlet at high-speed on.

Would creating a video that shows the result of a 100mm/min extrusion @ 245C help at all?

g.

[wonderemporium]

Ah, that explains it, thanks Gene! I thought I was going nuts there for awhile. I dropped my extruder temp to 240 and it's extruding nicely now. I've printed a few of the calibration cubes with each one getting better. I'm dialing in the retract settings. I would love to see a video, especially a close-up of how the extruder should behave during a print.

Should there be a pronounced delayed reaction in the plastic coming out of the tip as the feeds and extracts happen? What I mean is that when I advance the extruder motor, there is a little lag before the melted plastic comes out of the tip and then when I do a retract, it still comes out for a little while after the extract. It's like some extra material oozes out. On my prints, I'm getting extra plastic oozing out of the corners where the head stops for the retract. Increasing my retract to 6 and the retract speed to 50 helped but there is still a pronounced protrusion of extra material where the retracts happen.

I also seem to be starving for material a little bit, even at 30% feed rate. At faster feed rates its even worse. I'm wondering if I'm getting the proper amount of flow out of my tip but don't have any reference or prior knowledge to judge by.

I'm off to try another test cube with some more tweaks to see what happens. I'll post some pics after this print.

[geneb]

How fast and how far do you have your retract settings at?

g.

[Polygonhell]

Yes it's normal for there to be a delay in extrusion, it's made somewhat worse by the Bowden tube.

This isn't really an issue during the print, because it's about pressure inside the Hotend and because the retract/resume, should just provide a temporary lull in that pressure.

In terms of retraction during the print, put a mark on the outside of the larger gear and watch it during the retract, and make sure it returns to the same spot, it's very easy to get too agressive with the settings, and have the stepper skip in one direction or the other, this will either starve you of filament or provide too much.

[wonderemporium]

I've tried a big range of retract settings, from 1mm @ 20 mm/s up to 10mm @100mm/s and just about every combination in between with not much difference. I'm actually getting better results with no retract and fast non-printing moves since it races to the next spot and leaves thinner strings. It still leaves a heck of a mess at the entry and exit points though and I've yet to get an acceptable print due to this issue. I am dialing in some other settings and have some other problems that I will post separately. Until they are resolved, I can't be sure that it's only a retract issue but something doesn't seem right with the amount of extra ooze I get from the tip. I did check the gears on the extruder and I'm getting the same position so I don't think I'm losing and steps on the extruder motor.