Weird bridging issue!  

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andrew.s59
(@andrew-s59)
Eminent Member

hello everyone

So I have 3 x Prusa MK3 printers. All set up the same.

All three print well - but one of them cannot do bridging at all.

In trying to troubleshoot this - I have...

1. Changed the fan - no difference! And with both fans the printer checks it and is happy

2. Changed the fan shroud - Im actually using Volcano so Im using a modified shroud. But it made no difference. All the other machines are set up identically and bridge well.

3. All print files are the same on each printer, so its not a file issue. 

I cant for the life of me work out why im getting really really saggy prints! See the picture - that's a small rectangular part, and the sags are between grid infill. It would usually be completely flat there. All other parts print very well - calibration cubes are good.

Is there a setting on the printer that could be doing this?

Is there anything else I should check?

Can a bad nozzle do this? Im using steel .8 nozzles, and they are usually perfect..

Any advice appreciated

Andrew!

!

Posted : 30/12/2019 2:01 pm
bobstro
(@bobstro)
Illustrious Member

Have you done PID tuning for the temps you're using? Bridging will be very sensitive to temp and any variation may account for the difference you're seeing. 

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 : 30/12/2019 3:56 pm
andrew.s59
(@andrew-s59)
Eminent Member

@bobstro

That's a great idea! Trying it right now - thanks for that!

Posted : 30/12/2019 4:04 pm
andrew.s59
(@andrew-s59)
Eminent Member

That didn't work...

but I have a new idea... What if the flow rate is somehow too high, so too much plastic is coming out?

Posted : 30/12/2019 4:59 pm
bobstro
(@bobstro)
Illustrious Member

You could check out the extruder calibration routine on Matt's Hub, but most Prusa printers are within 1-2% as shipped. Can't hurt to verify though, and that's something that will be unique to each machine. I'd also open a case with PrusaSupport via online chat while logged into the estore. Good luck with it!

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 : 30/12/2019 5:14 pm
andrew.s59
(@andrew-s59)
Eminent Member

Ill have a look at that..

 

Could it be a damaged nozzle does anyone think? Like an internal deformity that sends the plastic out in a stream that isn't quite straight?

Posted : 30/12/2019 5:18 pm
bobstro
(@bobstro)
Illustrious Member
Posted by: @andrew-s59

[...] Could it be a damaged nozzle does anyone think? Like an internal deformity that sends the plastic out in a stream that isn't quite straight?

Oh, good thought. Yes, that could account for the problem. You've got it narrowed down to hardware at this point (I think). Consider a nozzle swap. Follow the E3D instructions closely, especially the bit about leaving a < 1mm gap between nozzle hex and heater block and doing final tightening at 285C.

Are the 08.mm nozzles E3D nozzles or generics? The generics vary a lot in quality and you might have one that has impurities causing inconsistent heating. The last pic is really odd in that it looks like it starts out well at the top, then goes nuts. Looks like the bottom part of the print is too cool to adhere and the weight of the larger extrusions pulls it down. 

Also check your fan cooling. Re-orient the part and see if the problems move with specific parts of the fan coverage.

Is this PLA filament?

 

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 : 30/12/2019 6:31 pm
andrew.s59
(@andrew-s59)
Eminent Member

@bobstro

Well, its an E3D nozzle - and its definitely in properly - Im going for a nozzle swap!

I thought in my ignorance that steel nozzles were pretty indestructible - but perhaps ive scratched it / deformed it somehow...

Love the idea about reorienting the part - will try that now with the old nozzle, trying to stay scientific and not change too many things at the same time!

Thanks so much for your thoughts on this - its really helped

Posted : 30/12/2019 6:52 pm
bobstro
(@bobstro)
Illustrious Member
Posted by: @andrew-s59

[...] Well, its an E3D nozzle - and its definitely in properly - Im going for a nozzle swap!

I thought in my ignorance that steel nozzles were pretty indestructible - but perhaps ive scratched it / deformed it somehow...

E3D produces high quality stuff, but nothing is 100% fail-proof. At least that's an easy check.

Love the idea about reorienting the part - will try that now with the old nozzle, trying to stay scientific and not change too many things at the same time!

That's something that could vary between physical printers. Check the fan and if you printed the duct yourself, check to make sure there's no support material stuck inside. Maybe swap cooling ducts as another test?

You might try one of the overhang tests if it's a quicker print. They're good at highlighting differences in cooling.  The https://www.prusaprinters.org/prints/3025-extreme-80deg-atom-3d-overhang-printed-on-a-prusa -" target="true">Atom80 testis a good one. You can scale it down for a faster test print. Would be interesting to compare prints of those among your different printers. Of course, a 0.8mm nozzle will produce bad overhangs.

 

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 : 30/12/2019 6:58 pm
andrew.s59
(@andrew-s59)
Eminent Member

IT WAS THE NOZZLE!

Switched it out, immediately fixed.

So there you have it - it looks like a bridging issue... But it was a small scratch in the steel nozzle, making the plastic extrude in a very slightly unpredictable way.

Mate, I appreciate your help with this - WIN!

Posted : 30/12/2019 7:47 pm
bobstro
(@bobstro)
Illustrious Member
Posted by: @andrew-s59

IT WAS THE NOZZLE!

Glad to hear you got it fixed. Not too many folks here have 3 to compare with, so that worked out well. I'll have to advise folks to buy 3 printers "just in case" from now on.

Do contact E3D and locate the nozzle packaging if you can. They may have production issues and knowing them, they'll want to be all over it.

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 : 30/12/2019 7:56 pm
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