ABS Heat End Jams

[ccholas]

I have been printing with my Rostock Max for the past two weeks without any flaws. However the past 3 prints have started, but the heat end has jammed in the middle of the print. I am running the nozzle temp at 250 (this was trial and error to get to this value, I have nice plastic flow). I disassembled the heat end both times and had ABS plastic stuck in the smaller teflon tube towards the tip. I pulled out the small teflon tube, pushed the jam through with a toothpick, tested whether there was drag with the 1.75mm ABS strand, there wasn't. I assembled the heat end, took the end to 250 and extruded 1000mm of plastic. It flowed consistently, no bubbles or stopping points. So I printed again. Some where in the middle of the next print plastic stopped flowing and it jammed again. The printer was able to get through about 20 layers before it jammmed. The plastic print was looking great until this happened. I cleared it and reprinted with the same results. I measured the hot end temp with a fluke thermo couple and digital thermometer and compared it to the thermistor value being read from the hot end. They are within 3 degrees of each other. I have checked the tightness of the heat end and nozzle. Both are securely tight when I start the print and when I check it after the failure occurs.

I am absolutely stumped on what this could be, I have searched the forums and web for similar issues and haven't found anything that has worked. One post mentioned that the thermistor could short out the Rambo board and blow the thermistor which he found was causing his failure. He fixed it with a new Rambo and heat end assembly. He shorted the thermistor wires, that hasn't happened to my printer. I am considering buying a new heat end assembly and another Rambo board as a brute force way to fix it. But I would like to avoid that costly repair if possible (I have already been through 1 Rambo board during the assembly process).

Does anyone have a recommendation?

[cambo3d]

250 is a bit high for abs, your risking melting/damaging your hotend, if your using the stock setup.

[Jimustanguitar]

Do you have the peek plastic between the two aluminum halves tight? How about the bowden adapter (it retains the other end of the teflon tube)? If you don't have an obvious mechanical or temperature culprit, I would suspect little chunks of grit in your filament. Do you have a different spool of plastic to test with? If that doesn't do it, I would measure the length of the teflon tubing inside of the hot-end and see if seemecnc says it's the proper length.

[ccholas]

Can you clarify your question? Do you have the peek plastic between the two aluminum halves tight? I assume you are talking about the Bowden extruder, I have adjusted the tightness so that I cannot stop it by pinching my fingers over the plastic strand before it goes into the extruder. I tested it with 1000mm of plastic after I cleared the first plug. And flow was fine.

I hadn't really thought about the spool of ABS. I have another spool of a different color and will try tonight. I will measure the teflon tubing as well. It is the original tubing that came with the hot end. But maybe it is off.

As for the temperature, I started at 230 and worked up to 250 in 5 degree increments. I was getting side walls that were pulling apart and plastic was not adhering in places. At 250 my prints really started looking good. I will back it down to 245 and try again. Maybe it is getting too hot for the teflon and maybe the teflon is swelling or something at temperature. Again I haven't had this issue until recently. But maybe it just took time to happen. Thanks for the input.

[Flateric]

At those temps you MUST have a fan pointed at the side of the hotend to prevent it melting and failure. Also be sure that it's flow does not reach you part when printing with ABS, or you'll have bad prints.

Do not point a fan at ABS parts being printed or they will delaminate or show other bad characteristics.

At 250c you are well above where you should be for temps. Unless you are printing crystal ABS high impact resistant. I worry your next post will be of a melted hotend issue at these temps.

[JohnStack]

I just jammed TWICE at 240 first layer/225 all layers after. I exhausted my single backup head supply. I blame my green filament and printing four prints without checking adjustments.

Anyway, on the subject of jammed heads, can you unjam them? What is 0.5mm so I can clean out the end that's easily accessible - like from Lowes or Home Depot?

On that topic, what is the general consensus for the best 3rd party heads? I might experiment a bit.

[geneb]

ABS is easy. Just soak it in acetone for a few hours. It'll dissolve the filament right out.

g.

[JohnStack]

The previous one that had stuck has been in a glass bottle filled with acetone for about three weeks! That didn't quite work for a .5 nozzle - but what did? My wife's #10 sewing machine needle and a little acetone (I think that was the size.) My mic measured it at 0.46. Since they have a chamfer on the side, it makes a nice little auger without damaging the brass.

[Polygonhell]

I've never had a jam with ABS I couldn't just heat up and manually push filament through to clear.
Most PLA jams I can clear by heating to 240 for say 30 seconds or so then manually feeding filament through.
I have had PLA jams where the oly way I could clear them was replacing the PTFE liner in the Hotend.

[JohnStack]

Good idea on both plastics.

When clearing my ABS jam, I had some carbonized filament that I had to remove.

[JohnStack]

Just had another jam and my temps went up to 260 without telling it to do so. Waiting on parts to rebuild. The peek plastic was a bit out, so it's rebuild time!

[jake]

so, how did you fix it?