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Nozzle hits prints off after about 450mm  

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(@)
Illustrious Member
RE: Nozzle hits prints off after about 450mm

When washing the sheet, running water should bead and sheet off; if water is wetting the surface there is something on the PEI. 

After washing my print sheets (smooth and textured), there is usually so little water remaining the paper towel I dry with only has a few damp spots when done. Not even wet. And, I use gallons of hot running water to thoroughly rinse off everything (the soap simply lifts the oil, the water rinses it away). It's the gallons that make the difference between alcohol (usually a dram or two) and soap and water (usually gallons).

Posted : 29/04/2021 5:31 pm
Milazzone
(@milazzone)
Eminent Member
Topic starter answered:
RE: Nozzle hits prints off after about 450mm

Sure, I'll keep that in mind. When I washed it the first time it more rolled off as a sheet a bit slower than beading off but was pretty dry already before I actually used a paper towel to dry it.

Posted : 29/04/2021 7:15 pm
ssill2
(@ssill2)
Noble Member
RE: Nozzle hits prints off after about 450mm

Dawn platinum does the trick.  The only time you might have to consider glue with PLA is with prints that have a large flat surface that covers most of the bed.  this is when you have to consider other adhesives.  With PETG I've seen the print pull the corners of the bed up with just glue stick!  

Posted : 30/04/2021 12:56 am
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(@)
Illustrious Member
RE: Nozzle hits prints off after about 450mm
Posted by: @ssill2

Dawn platinum does the trick.  The only time you might have to consider glue with PLA is with prints that have a large flat surface that covers most of the bed.  this is when you have to consider other adhesives.  With PETG I've seen the print pull the corners of the bed up with just glue stick!  

I disagree here. Glue is never really needed on a smooth sheet. If printing large areas, 200x200mm, simply add bed heat; and the PLA stays attached. I've even gone as far as keeping the bed at 75c.  You can also add round corner coupons/brims to help reduce the stress at sharp corners. It's been my experience that short of superglue nothing will keep parts from warping when they want to warp - but higher bed temps can help keep the warp under a modicum of control; as can an enclosure. 

That said, there are products made for keeping ABS attached that some have found to work well even with PLA. But the ones that work are expensive: $20 a bottle and up.

Posted : 30/04/2021 2:52 am
ssill2
(@ssill2)
Noble Member
RE: Nozzle hits prints off after about 450mm

@tim-2

I would think for a large print however that keeping the bed 10-15C higher than the glass transition temp of the material would result in the weight of the print squishing down the lower layers of the model.   I'm certainly willing to up my temp for for things like PLA and PETG if just increasing the bed temp does it but I've always steered away from that because of the assumption that if the material is super malleable on the plate that it would start to deform.

 

Posted : 30/04/2021 11:29 am
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(@)
Illustrious Member
RE: Nozzle hits prints off after about 450mm

You may suffer a bit of elephant foot on the contact layer, but the end results I've experienced have been insignificant. And, if you think it might be an issue, Pslicer has elephant foot compensation a click away.

Posted : 30/04/2021 4:26 pm
ssill2
(@ssill2)
Noble Member
RE: Nozzle hits prints off after about 450mm

@tim-2

I guess it would depend on how much heat radiates up from the first layer into the rest of the model.  But if I run into issues with warping again maybe I'll give it a try.  Thanks.

Posted : 30/04/2021 4:29 pm
mobius
(@mobius)
New Member
RE: Nozzle hits prints off after about 450mm

I have exactly the same issue, with a printer that i received two days ago.

It's my third printer so I know how to clean a bed 🙂

I feel that there is a jump down on Z axis at 3,417 cm
And as everybody can see on milazzone video, the noozle hit the top of the printed parts.
So it's clearly not an issue with a not clean Bed

Posted : 02/05/2021 12:34 pm
ssill2
(@ssill2)
Noble Member
RE: Nozzle hits prints off after about 450mm

I think with a tall thin model you might actually need to slow down the print speed a bit at least on the layers you start seeing it move the print.   You can do this in the slicer with modifiers.  I've had to do this with tall thin stuff before even when the over print wasn't thin but some feature on the print was.

Posted : 02/05/2021 1:02 pm
mobius
(@mobius)
New Member
RE: Nozzle hits prints off after about 450mm

I tested :

- Slower print

- More retract

- Less temperature

But already the same result exactly at 34mm

 

Posted : 02/05/2021 2:24 pm
Neophyl
(@neophyl)
Famed Member
RE: Nozzle hits prints off after about 450mm

@mobius

If you think the extruder drops down at 34mm then print a 40mm cube, with 2-3 perimeters and 20% infill.  If its drops down then it will pop your cube off the same as the benchy.  I don't think it will unless you have a printer that is defective.  About the only thing that could cause that is faulty stepper motor wiring such that the wiring is flexed when in certain positions.  

The reason its popping off the bed with the benchy is the window/door arches on the model.  At around 34mm those edges are overhangs as the angle of the arch means they print mostly unsupported by the layer below.  When those edges cool they can curl upwards.  This makes them higher than the surrounding layers.  On the next pass the nozzle then hits those curled up areas. 

IF your bed adhesion is good the bump is survivable and the hot nozzle will in effect remelt and 'iron' those curled up areas back down.  However if its is only ok then the bump will be enough to knock the part loose.  Think of it as a stress test, which is exactly what a Benchy is supposed to be.  

There are many different factors that have been mentioned  on this thread and they all interact.  If your cooling is actually not as good then those areas instead of curling up can droop down and so don't get in the way on the next pass.  Similarly if printing in an enclosure the plastic will cool/contract differently (or not as much) so that will effect the prints.

Of those things you tried, retraction will have no effect, temperature could, printing slower could but as many people have pointed out Bed adhesion not being spot on will make a huge difference to if it can survive a bump or not.  You could also insert a fan reduction command before those layers to give less cooling, or set bridge fan speed lower.

Posted : 02/05/2021 3:26 pm
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(@)
Illustrious Member
RE: Nozzle hits prints off after about 450mm

@mobius

And in agreeing with Neo on this, the printer - unless defective or a bad slice with poorly written custom commands - is not suddenly jumping down during printing.

Many things happen during printing of overhangs. One is plastic curl due to cooling differentials from the print fan airflow. And yes, this has ruined many prints of mine, too, before I fully understood what is happening and now plan for it.

If you have adhesion issues (and you'd be surprised how many print issues derive from bed contamination) this curl becomes a serious problem. You'll notice in the OP the place where detachment occurs is always at the arch of the Benchy door or window. The place where curl is most prevalent. The curl is quite visible in your photos.

Since we can't see the bottom of the print, hard to say if you are also having layer one issues or are using the Prusa textured sheet. Snap a photo of the Benchy fails so we can see what's going on there. And let us know which sheet you are using.  I can say up front, if you are trying to print PLA on a Prusa textured sheet, you will have an uphill battle. There seem to be good ones and bad ones. Bad ones end up relegated for printing PETG or ASA.

This post was modified 7 months ago by --
Posted : 02/05/2021 8:40 pm
Diem
 Diem
(@diem)
Noble Member
RE: Nozzle hits prints off after about 450mm

@mobius

the noozle hit the top of the printed parts.
So it's clearly not an issue with a not clean Bed

This is exactly what happens if bed adhesion is poor.

Cheerio

Posted : 03/05/2021 1:36 am
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(@)
Illustrious Member
RE: Nozzle hits prints off after about 450mm

And anyone who professes to know how to clean the sheet and shows a dislodged part with a very minor curl issue ... well - the credibility score just tanked. So I am moving on to other threads.

This post was modified 7 months ago by --
Posted : 03/05/2021 1:42 am
Milazzone
(@milazzone)
Eminent Member
Topic starter answered:
RE: Nozzle hits prints off after about 450mm

While I think Tim's reaction is a bit harsh here; knowing how to clean a bed and a bed actually being clean are two different things from the experience I gained. Mainly even after cleaning my bed well, I could still notice streaks and even now it's not perfect. I think either the Windex I used on it on day one might have had an oil in the fragrance that wasn't nice to the bed (it was a different scent than original windex); or it wasn't quite perfect from the factory (I obviously didn't notice the difference before cleaning). It was easiest to see in comparison to the other side of my bed when washing. I might have to try an acetone wash to see if I can really bring that side back for real later.
I think the only way to be CERTAIN it's not a bed adhesion problem (particularly in this case where it's seemingly the same curl issue I had) in my opinion would be to try it with a glue stick after giving your first layer another look. If it still has problems either you might actually have a defect, or it was constructed incorrectly. This isn't to say that you should necessarily be using glue stick all the time, but rather I was using it as a tool to prove to myself that everyone saying it was an adhesion problem wasn't just pulling my leg as a newbie or something.
There are other ways to combat curl, as others stated above, but for a typical benchy this should be recoverable with relative ease with good bed adhesion.

Posted : 03/05/2021 2:33 am
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(@)
Illustrious Member
RE: Nozzle hits prints off after about 450mm

A streak test is easy. Dampen a piece of paper towel with alcohol, wipe it across the sheet. There should be ZERO rainbow effect and ZERO visible streaks after the alcohol has evaporated. The print sheet is the same color and shade everywhere when it is clean, and any discoloration is a sign of foreign contaminates on the surface.

As for being harsh, it gets frustrating to hear a guy having problems that are obvious contamination issues say that's not what is happening. I should be smarter and just change channels... but I worry about the other guy that comes along and might buy into the BS.

As for a glue stick ... that is laughable. The purpose of the glue stick is to REDUCE adhesion - not improve it (well, for PETG - and it may help ABS adhere - but for PLA it is like adding sugar to a diet coke).

This post was modified 7 months ago 2 times by --
Posted : 03/05/2021 3:05 am
Milazzone
(@milazzone)
Eminent Member
Topic starter answered:
RE: Nozzle hits prints off after about 450mm
Posted by: @tim-2

As for a glue stick ... that is laughable. The purpose of the glue stick is to REDUCE adhesion - not improve it (well, for PETG - and it may help ABS adhere - but for PLA it is like adding sugar to a diet coke).

If that's really the case..... then why the heck did my print fail after a wash but was just fine after gluestick? That really sounds like you're just trying to sound like you know everything and a new person's experiences are invalid. Sounds like my gluestick test was a rousing success then and I was able to super overcorrect my bed problems on the last wash which still showed streaks... 😝 

Posted : 03/05/2021 3:21 am
Milazzone
(@milazzone)
Eminent Member
Topic starter answered:
RE: Nozzle hits prints off after about 450mm

I won't say I know all the in's and outs of what's really going on and I could easily have missed things that seem common. Just honestly confused by that comment as I clearly had issues before the gluestick. Now I'm printing along just fine after scrubbing quite a bit harder and effectively washing it 3 times in a row after that gluestick run. Haven't needed it for my latest benchy and a couple other small prints, so that's good at least.

Posted : 03/05/2021 3:31 am
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(@)
Illustrious Member
RE: Nozzle hits prints off after about 450mm

Cleaning the print sheet is - well - ripe for discussion. There are those that find alcohol works great. But when you dig deeply at their methods, they use a lot of alcohol in the process, large rags, and rarely touch their print sheets.  New users tend to think a dab of alcohol is enough, and generally use rubbing alcohol rather than a more pure variety. Then add the complexity of textured versus smooth ... another realm of whys and wherefores. In the end - soap and water is best. Why? Volume. A gallon of ho water removes more contaminant and leaves a lower percentage of it on the sheet. It is simple numbers.  One ounce of alcohol vs 128 ounces of water times five (a couple minutes at most sinks). Do you use a full ounce of alcohol to clean the sheet? 

If you have enough oil on the sheet - a gluestick will help displace some of that oil. It is why a gluestick might help. And yeah - I've been there, using a gluestick because my print sheet was filthy dirty - before I learned that soap and water works better. Why? Detergents clean off organics by surfaction, and not by bringing them into a solution. A solution always leaves a film - as you wipe away the alcohol, if you don't get it all, the alcohol evaporates leaving the oils in solution behind. 

If you washed the sheet, and the subsequent print failed, and gluestick helped, then I'll say you didn't do a fair job washing the sheet in the first place (or the sheet is a Prusa Textured Powder Coated PEI sheet).  The common mistake made at the sink is people grab the closest sponge and scrub.  Either use a brand new 3M scratchless scrubber you just removed from its plastic wrap - or use a new paper towel. Wash until the water begins sheeting off. Then dry what drops remain with another new paper towel still handling the sheet only by the edges. If any areas remain where water isn't sheeting off or beading, start washing again because the sheet isn't clean. 

And yeah - I am kind of a dork about this because so many folk have adhesion issues that are so easily fixed with soap and water.

Posted : 03/05/2021 3:46 am
Milazzone
(@milazzone)
Eminent Member
Topic starter answered:
RE: Nozzle hits prints off after about 450mm

Yea, given that information I'm still not 100% sure why my sheet isn't beading off quite the same as the other clean side (keeping it clean for future use when I get better at this). I scrubbed with a few new paper towels and plain old original dawn soap as you suggested and it's just not quite as good as the other side. Did it about 3 times in one sitting at the sink (maybe 15 minutes of scrubbing), but right now I don't have the printing issues I had before, just mild streaking on the build plate. I'm still thinking the windex I used on day one was a factor and some part of the fragrance or if it might have had some differences to the formula might have left a harder substance to get off on my sheet.
 
If I do an acetone wash soon I'll likely report that back if there was a change. Oh well, live and learn. This time it just seems to be "not all windex is the original windex mentioned for cleaning the build plate" XD

Posted : 03/05/2021 4:03 am
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