New heat block. What changed?

I've been printing these ABS caps as thread protectors:





Everything was working great and I'd printed about 20 or so until I had a part come loose and ended up with a bird's nest of filament engulfing my hotend. I managed to get it loose and replaced it with a spare block that was essentially identical. I used the same heater (40 watt) and thermistor in the new block, and added a new nozzle from the same lot I'd purchased earlier (0.4 mm MK8). Using the exact same settings as before (in fact, the same gcode file produced from cura) I'm getting these ugly blobs on the thread edges of my prints:



I can't think of what might be different from the switched heat block that could be causing such a dramatic difference in quality.

This is a prusa I3 clone loosely based on the Geeetech I3 with a MK8 hotend. This is my replacement heat block, which is essentially identical to my old one (now encased in ABS). I wrapped it in some fiberglass mesh and capton tape (the original had a similar wrapping):



Any ideas?

Edited 1 time(s). Last edit at 06/07/2016 07:33AM by hoxsiew.

I don't thinkt this comes from the heater block. My first guess would be the nozzle itself.

---

[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

Agree with Srek, most likely is a bad quality nozzle.

Since it is ABS leave your old nozzle in a bath of acetone and once all ABS cleaned put it again and see.

Is your heat brake pipe full metal or have PTFE liner?

It has a PTFE liner, as did the previous. It is different in that the previous pipe was smooth until that last few millimeters which were threaded. The new one is threaded through the whole length. It is held in place by a set screw in the extruder block so the threading doesn't matter (except possibly less thermal contact with the extruder block).

I purchased several nozzles at the same time (from http://www.vicious1.com/product/0-4mm-nozzle/ )so I can try another from the lot, but I'll try the acetone soak on the old one if the new ones give the same results.

Edited 1 time(s). Last edit at 06/07/2016 07:57AM by hoxsiew.

im just guessing but if you didnt seat the nozzle at the exact same height as the last one, as well as the block, i figure your retraction settings would have to be redone? if its off by a mm or anything it would change the heat distribution from your last nozzle and might cause a need for increase/decrease in retraction length or speed.

i dont know though im really just guessing, try increasing your retraction by a mm and see what happens

I hadn't even considered that, but it makes perfect sense. Not only just the heights, but the fact that there's going to be a considerable thermodynamic difference between the threaded and non-threaded tubes.

Thanks!

Have you messed with your thermistor when replacing the blocks?

I did have to pull the thermistor out of the old block through a birds nest of filament and worried that I might have damaged the leads, but it seems OK and give reasonable values on temperature.

I think I've since figured it out and, as suggested earlier in the thread, it seems to have been the nozzle. I soaked my old one in acetone (took 3 or 4 days to fully dissolve the ABS), then installed it into the new block. It's making good prints again.

Thanks to Srek and ggherbaz for suggesting the nozzle.

Quote
hoxsiew
I did have to pull the thermistor out of the old block through a birds nest of filament and worried that I might have damaged the leads, but it seems OK and give reasonable values on temperature.

I think I've since figured it out and, as suggested earlier in the thread, it seems to have been the nozzle. I soaked my old one in acetone (took 3 or 4 days to fully dissolve the ABS), then installed it into the new block. It's making good prints again.

Thanks to Srek and ggherbaz for suggesting the nozzle.

Awesome!!

Is there any chance of some close-up photos of the 'bad' nozzle tip? It would be interesting to see if we could figure out what is different.

It's hard to get my camera to focus that close, and this is the best I could do. It may be dented a little on on side, or perhaps just drilled a bit off center. Keep in mind that there is a slug of grey ABS in there too.

Thanks for giving it a try. It certainly looks a bit asymmetrical, with the face not being circular.