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Brand New Official Hot End, Now Overhangs are Trash  

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TwoBallScrewBall
(@twoballscrewball)
Trusted Member
Brand New Official Hot End, Now Overhangs are Trash

Installed and calibrated a new hot end direct from Prusa in my MK3S+.   I am printing with PETG.  It prints beautifully, except that now even simple overhangs that I had absolutely no problem with before, are coming out like garbage now.   Attached some photos.  I have tried raising and lowering the hot end temp (I print at 240, so lowered to 220 and raised to 250) without any luck.   

Any ideas as to what might be causing this?  Again, these were printing fine with the old hot end. 

 

This topic was modified 2 months ago by TwoBallScrewBall
Posted : 10/05/2021 4:27 pm
Cine Zone
(@cine-zone)
New Member
RE: Brand New Official Hot End, Now Overhangs are Trash

Maybe your first layer height changed slightly with the new hotend and you need to recalibrate

Posted : 10/05/2021 4:38 pm
TwoBallScrewBall
(@twoballscrewball)
Trusted Member
Topic starter answered:
RE: Brand New Official Hot End, Now Overhangs are Trash

I did a full Z offset recalibration, also a full XYZ and also an Estep calibration just to be safe, since the poor printer has been going just about nonstop since I got it in December 🙂  First layers are great.   Anything without an overhang is great.  It just does what I showed above if there is any overhang.   

I can't flip over those items as they are hollow and would require tons of support if I did so. 

 

Posted : 10/05/2021 4:41 pm
bobstro
(@bobstro)
Illustrious Member
RE: Brand New Official Hot End, Now Overhangs are Trash

Have you done a PID tune since installing the new hotend? It shouldn't cause exactly the problem you're seeing, but it will help tune the heating algorithm. You do appear to have a bit of warping in the corners. Are you running fan cooling with PETG? Overhangs can be very tricky with little or no cooling, but PETG prints best without a lot of cooling. I found I had to turn on 30% fan speed for some parts of my prints with overhangs when printing with PETG. A lower layer height can also help in those areas.

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 10/05/2021 4:51 pm
TwoBallScrewBall
(@twoballscrewball)
Trusted Member
Topic starter answered:
RE: Brand New Official Hot End, Now Overhangs are Trash

Have not done a PID tune, ever.  I'll give that a shot. 

 

Posted : 10/05/2021 4:59 pm
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(@)
Illustrious Member
RE: Brand New Official Hot End, Now Overhangs are Trash

@twoballscrewball

Since you had everything apart - the aim of the print cooling fan shroud can change - and is critical to adequate overhang performance. Make sure the shroud points at the nozzle, not the heater block.

Or if by chance you also installed a new cooling fan to go with that new extruder. Two 5v 50 mm radial fans can look identical but blow completely different air flow rates. It's actually surprising just how much difference there can be. So aftermarket fans are probably worth avoiding unless you have carefully considered the air flow at pressure curves.

ps: I agree those prints you've shown look pretty bad. Something is off. 

This post was modified 2 months ago by --
Posted : 10/05/2021 5:51 pm
TwoBallScrewBall
(@twoballscrewball)
Trusted Member
Topic starter answered:
RE: Brand New Official Hot End, Now Overhangs are Trash

Does this look right?   I did take quite a bit apart to get it cleaned up.   

Posted : 10/05/2021 6:02 pm
bobstro
(@bobstro)
Illustrious Member
RE: Brand New Official Hot End, Now Overhangs are Trash
Posted by: @twoballscrewball

Does this look right?   I did take quite a bit apart to get it cleaned up.   

It looks very clean. Just a couple of things:

  1. It looks like the thermistor cable is dangling below the blue sock. Move those cables up out of the way so they can't snag prints.
  2. I notice you're using the "Pro" style silicone sock. Those are great in theory, but that small nozzle opening can cause problems if the sock shifts. I've gone over to the "non-Pro" style with the larger opening around the nozzle. If nothing else, consider wrapping some wire around the sock to keep it from sagging.
My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 10/05/2021 6:11 pm
TwoBallScrewBall
(@twoballscrewball)
Trusted Member
Topic starter answered:
RE: Brand New Official Hot End, Now Overhangs are Trash

Its funny I also noticed that cable in the photo and I got it moved.   It was above the bottom of the heat block, well above the nozzle, but I didn't like the way it looked either. 

Just did a PID tune and am giving it a shot with the fan disabled.   Let's see what happens. 

Good info on the sock.   I didn't know socks existed for the first few months I owned the printer, so as you can imagine my original hot end / heat block was quite a mess.  😀

 

Posted : 10/05/2021 6:20 pm
cwbullet
(@cwbullet)
Illustrious Member
RE: Brand New Official Hot End, Now Overhangs are Trash

@bobstro

I have had the same shift iss with silicone socks.  It can cause a doozy of a blob.  

--------------------
Chuck H
3D Printer Review Blog...
Posted : 10/05/2021 6:34 pm
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(@)
Illustrious Member
RE: Brand New Official Hot End, Now Overhangs are Trash

@twoballscrewball

From my perspective, the shroud looks to be directing air at the heater block - a bit high. I'm not sure that is or isn't normal for an S or S+. 

Another question: is the sock a new addition since rebuild? Or have you been using one for a while, even on the old hot end?  I ask because with the shroud looking high, and if the sock is new, you have a totally different airflow that may easily change overhang performance.

ps: and as Bob said, the narrow opening on the pro sock will eventually start catching on curls and artifacts that form on parts. I cut the thin part out and then started buying the non pro versions, too. Just less work. And the wire trick is a good suggestion - just make sure the wire isn't anywhere near the heater core wires.

This post was modified 2 months ago 2 times by --
Posted : 10/05/2021 6:51 pm
TwoBallScrewBall
(@twoballscrewball)
Trusted Member
Topic starter answered:
RE: Brand New Official Hot End, Now Overhangs are Trash

I know a little something about blobs..... This is what happens when you accidentally select the PLA profile in slicer when printing PETG, kick off the print then go to bed.......... 

 

Posted : 10/05/2021 7:01 pm
TwoBallScrewBall
(@twoballscrewball)
Trusted Member
Topic starter answered:
RE: Brand New Official Hot End, Now Overhangs are Trash

I was running the same socks on the previous hot end, with no issues with the overhangs.   

When this print I have running completes, I'll see if I can reposition the part fan shroud at all, but I believe it is in the correct location.  Printer is a 3+.

Posted : 10/05/2021 7:03 pm
TwoBallScrewBall
(@twoballscrewball)
Trusted Member
Topic starter answered:
RE: Brand New Official Hot End, Now Overhangs are Trash

245 degrees, fan completely disabled.   So I'm wondering if I had poor airflow before I took apart the extruder and cleaned everything out, and now that it's clean I'm getting too much cooling in places..... ?

Posted : 10/05/2021 7:21 pm
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(@)
Illustrious Member
RE: Brand New Official Hot End, Now Overhangs are Trash

@twoballscrewball

I can say with 100% confidence your prior hot end was NOT assembled correctly - the leaks are just too compelling. lol.

The new hot end may need tweaking if you made adjustments to compensate for that broken build you had before.  Fan was also probably maladjusted with the heater block - or could even had been blowing below the block if the heat break was positioned wrong. Hard to say - but you have a new world to learn: be patient and adjust methodically.

 

This post was modified 2 months ago 2 times by --
Posted : 10/05/2021 8:02 pm
cwbullet
(@cwbullet)
Illustrious Member
RE: Brand New Official Hot End, Now Overhangs are Trash

@twoballscrewball

That print looks pretty good!

--------------------
Chuck H
3D Printer Review Blog...
Posted : 10/05/2021 8:18 pm
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