Same G Code, Different results?

[sTaLa]

So here's the thing.

I just printed a Chest set for my kids. I did the whole set in one print. But I broke one of the pawn while removing it.
Luckily, the models were still in my simplify 3D screen. So I simply removed all the other models from the screen, only keeping the pawn. I changed nothing within the parameters.

But I get two different results as you can see on the picture below. Does it have to do with cooling/bonding of the layers?

The one on the left was printed with the whole set.
The one on the right was printed alone.

I was print PLA
210C
Bet at 70C
M2 RevE

Thanks!

[Matt_Sharkey]

I'm not sure why your second print is less stringy but it does look a bit more melted. This happens when you print small areas on a single object. The layers get very hot because they are never given a moment to cool and become more pliable. to prevent the "heat soak" you can either try to add more cooling or just print a second copy at the same time, that way each layer has time to cool before the next layer.

[sTaLa]

Yeah I agree with what you say. The thing is, I like the one on the right much more, that is, the one that was printed alone...
I would like to replicate this quality with the whole set in one print...

[Jules]

Your second print doesn't show travel threads/strings because the nozzle wasn't traveling to other areas to print other parts. The only way to avoid them entirely is to just print one object at a time.

You can try to minimize them by pointing a fan at it (more cooling that Matt recommended), lower the extruder temp by a couple of degrees, or try to increase the retraction just a little bit. It might knock them down.

I think some of the guys just burn those little threads off by waving a lighter or hairdryer at the piece. (Carefully, or you will melt it.)

[sTaLa]

Thanks for your inputs! I will work on cooling and retraction.

There is something I do not understsand tough. If the strings are created by the nozzle moving from one part to the other, ther should be about 2 strings per layer, the one coming from the precedent part and the one going to the next part.

What I can see on the left part tough is a lot of strings between each "spiral column" of the pawn. While there is not such screens on the right pawn...
You can also see holes on the left part which are not on the rigth part. These I have no clue where the come from.

But what mystifies me most are the strings between each column on the left part only...

[Jules]

If the strings are created by the nozzle moving from one part to the other, ther should be about 2 strings per layer, the one coming from the precedent part and the one going to the next part.

Only in a perfect world, and printing with plastic doesn't work that way.

What I can see on the left part tough is a lot of strings between each "spiral column" of the pawn. While there is not such screens on the right pawn...
You can also see holes on the left part which are not on the rigth part. These I have no clue where the come from.

But what mystifies me most are the strings between each column on the left part only...

That area might have been blocked from the fan, (or facing away from it), and heat built up, causing the filament to get a little runnier there. Heat soak will also cause holes and slumping/warping in overhang areas, and there's a little bit of overhang there where the threads and slumping seem the worst.

Point a small desk fan at the back of the bed and you'll see a lot of those problems go away. But if you are going to load up the plate with a lot of prints that potentially block air flow, you are going to see some issues like this....maybe you could try printing a few at a time instead of the whole batch at once. That air has got to get in there and cool the parts as it prints, all the way around each part. Any part that doesn't get hit by the fan is going to show those kind of issues, and sometimes just on the back side that the fan doesn't hit.

3D printing is always a series of compromises - do it slowly for best quality (one print at a time) or do it quickly and be prepared to do some cleanup after (all the pieces at once.)

[sTaLa]

I've got to thank you Jules for involvement on that forum. I've read countless of your threads prior to asking questions and I have to say they got me going pretty as I did pretty neat things!

I read that fan thing from you in one of your post, so I installed thins 120 mm fan I had laying around (yeah I printed a bracket to hold it):


But it sent me into difficulties on thin wall parts (0.030'' wall). As the wall next to the fan just tilted and was not completed. I ended up turning it off for the last week as I think the airflow must be too much. I jsut ordered Coolant Pipes that I intend to use to have the air flow as uniform as possible on the whole bed.

So to go back to that chess set: both prints were done using only the MG bed fan. But pawns and pieces are so small, I am having a hard time figuring out how the air flow from the 50mm fan could not go to the part that is being printed? I mean some of it is surely blocked by teh part in front of it if there are too close, but you guys think that air flow could be the root cause?

[Jules]

some of it is surely blocked by teh part in front of it if there are too close, but you guys think that air flow could be the root cause?

Yep!

Let me tell a quick fan story.

Back while I was learning to use mine, I saw that something like your issues was happening on the back of the print that faced away from the fan, so I licked a finger and stuck it under the air flow from the bed fan. My finger barely got cool an inch away from the front of the fan. (Then the hot nozzle brushed my finger and I toasted myself, so do not stick your moist finger under the bed fan while the damned thing is moving!)

The computer style fans just don't move much air, and depending on which way they are pointing, they can leave spots un-cooled, particularly on the backs of prints that do not face the fan directly. If there is an overhang area that faces away from the fan, and you are printing PLA, you are going to have trouble. (Not all filaments have trouble with overhangs, but PLA does if it is not cooled quickly.)

At the time, the only thing I had on hand was a fold-out paper hand fan. So I took that and waved it vigorously at the back of the print. Problem stopped.

I tested about half a dozen different fans. A couple of little hand held battery operated ones actually worked pretty well, but I had to stand there and hold them on the print, so that wasn't a great option. Some Vornado style ones put out too much air, others didn't put out enough. Finally got really good results using this small footprint desk fan pointed at the back of the prints, with the regular bed fan pointed at the front. The air on this one comes out at at a high enough level that it moves across the top of the plate while the bed is in the elevated starting position.

https://www.amazon.com/gp/product/B000M ... UTF8&psc=1

That little fan sits next to the printer, and if I need it for a print, i turn it on. I don't need the fan for every print, and I don't need it for other filaments. I only turn it on for PLA prints with an overhang that I can't rotate around to face the fan at the front.

Wasn't worth it to me to try to modify the machine with special brackets and shrouds then for just the few prints that needed it, but several of the guys created some that they like. You can find them in the Modifications section if you do a search for shrouds:

viewtopic.php?f=10&t=2136

http://www.thingiverse.com/thing:1305933

http://www.thingiverse.com/thing:724933

Eventually, i did wind up creating a simple 15 minute motor fan guard modification that repositions the bed fan right in front of the nozzles for the dual that solved a lot of problems with oozing out of the left nozzle. It's also a bit quieter than the fan guard provided by MG and moves more air to the extruder fan. So i put one of these on the machine and use the back fan when I need it, and I get really good prints now.

Dual Fan Guard Modifcation: http://www.thingiverse.com/thing:1163035

Any of those solutions work just fine. You just need to make sure to get good air circulation all around for certain prints....it really is that important for PLA with overhangs.