Large printed parts are not flat even though they don't unstick from bed  

RE: Large printed parts are not flat even though they don't unstick from bed

Posted by: @tracy

 

Posted by: @justinas

I just tried again, bumping the temperature to 100°C. Without glue, PLA sticks like crazy. With glue, it doesn't stick at all, same as with any other temperature.

How did 100°C affect warping?

I printed that initial part (the one seen in my first post on this topic) at 100°C first layer, 90°C the rest of the layers. Adhesion was perfect, but as you can see, it warped really bad. Like others said, lower bed temperatures should decrease warping, but then I get bad adhesion. And with PVA glue stick, adhesion is pretty much non-existent with anything between room temperature and 100°C.

RE: Large printed parts are not flat even though they don't unstick from bed

I've never seen glue stick negatively affect the adhesion of PLA, and I've never had to go to 100 degrees even for large object. I'm just saying that to explain why I'm confused over what's going on here. I took a look at your settings. I'd try to reduce the perimeters to 3 and infill to 10% gyroid, to reduce material, and take the first layer to 0.2mm to get more squish. But I still don't see why you're not getting adhesion at much lower temperatures...

RE: Large printed parts are not flat even though they don't unstick from bed

Posted by: @fuchsr

I've never seen glue stick negatively affect the adhesion of PLA, and I've never had to go to 100 degrees even for large object. I'm just saying that to explain why I'm confused over what's going on here. I took a look at your settings. I'd try to reduce the perimeters to 3 and infill to 10% gyroid, to reduce material, and take the first layer to 0.2mm to get more squish. But I still don't see why you're not getting adhesion at much lower temperatures...

I kind of need these perimeters for longitudinal strength on the edges and the ribs... Anyway, thing is, even the very first lines (brim) don't stick to PVA glue, so the rest of the settings don't matter, I believe. Perhaps the PVA glue I have is just not the right formulation for this.

What about a raft instead of glue, say, 10 layers? Would having some distance between the bed and the actual part reduce this post-print warping, or is it likely to end in failure mid-print?

RE: Large printed parts are not flat even though they don't unstick from bed

This is odd. Which glue are you using exactly?
I have experience with "Uhu Stic" and "Kores" and both work on the smooth Prusa flex sheets, as long as you keep the glue layer as thin as possible, yet covering the whole area. If you have excess glue the first layer can be a big mess.

I haven't tried other adhesives. Some rely on the heat for strong binding, so that parts are easy to remove when the bed is cooled down. That is obviously not what is needed for this purpose. Maybe I am wrong with Magigoo though, as it appears to be also a thermally activated adhesive. There are use cases reported without heating the bed though. So who knows. Maybe it does work, a bit expensive though if you don't need it for anything else.

PS: for optimal results one should remove all the glue before each print and freshly apply a nice even but very thin layer of glue. Generally the z-offset that works without glue at 60°C best should be also close to what is best for 40°C with glue.

RE: Large printed parts are not flat even though they don't unstick from bed

Regarding a raft, I haven't made good experience with those if the aim is to reduce warping. but I mean you can try if you want. It should not fail but I am not sure if you'll end up with less warping. Also the underside will look not nearly as nice if you print it on top of a support raft.

RE: Large printed parts are not flat even though they don't unstick from bed

Posted by: @thejiral

This is odd. Which glue are you using exactly?
I have experience with "Uhu Stic" and "Kores" and both work on the smooth Prusa flex sheets, as long as you keep the glue layer as thin as possible, yet covering the whole area. If you have excess glue the first layer can be a big mess.

I haven't tried other adhesives. Some rely on the heat for strong binding, so that parts are easy to remove when the bed is cooled down. That is obviously not what is needed for this purpose. Maybe I am wrong with Magigoo though, as it appears to be also a thermally activated adhesive. There are use cases reported without heating the bed though. So who knows. Maybe it does work, a bit expensive though if you don't need it for anything else.

PS: for optimal results one should remove all the glue before each print and freshly apply a nice even but very thin layer of glue. Generally the z-offset that works without glue at 60°C best should be also close to what is best for 40°C with glue.

This is the glue stick I'm using:

The procedure you described, I actually followed to the letter (other people in this topic suggested the exact same). I always wash the sheet first with hot water and soap, clean thoroughly, don't touch it, dry it, place it on bed, apply one very thin coat (one pass with glue stick), let it dry, and then start printing at 40°C, using the same Z offset as without glue (but I also tried Live Adjust Z to raise or lower the nozzle). 

And PLA just doesn't stick to the bed, not even a little. The temperature seems to make no difference either, it's almost like that that PVA glue is a non-stick spray or something. I guess this particular brand is just not suitable for this application...

RE: Large printed parts are not flat even though they don't unstick from bed

Just to ask something that maybe should have been asked earlier — is this experience of PLA not sticking unique to this brand or are you seeing it with other brands as well?

RE: Large printed parts are not flat even though they don't unstick from bed

Posted by: @fuchsr

Just to ask something that maybe should have been asked earlier — is this experience of PLA not sticking unique to this brand or are you seeing it with other brands as well?

I actually never used PVA glue with PLA filament. I used it with some other filaments that stick to the bed too much - so to protect the sheet. For that, this PVA brand worked well. I don't have any other brands to try right now, but I will try to purchase several different sticks tomorrow.

RE: Large printed parts are not flat even though they don't unstick from bed

Sorry for being ambiguous. I meant the filament brand.

RE: Large printed parts are not flat even though they don't unstick from bed

Posted by: @fuchsr

Sorry for being ambiguous. I meant the filament brand.

Oh, sorry, that was my mistake. I have several filament brands that I tried already with this PVA. Prusament, Devil Design, Fiberlogy, also some unbranded generic Chinese filament. None of them stick any better than the others.

RE: Large printed parts are not flat even though they don't unstick from bed

@justinas

I just blew through 2 pages of this thread without reading any of the other answers, so forgive me if this has already been suggested.

It's possible, even likely, that your bed is bowing in the middle as the build surface heats up, and since your part is no longer lifting up from the bed it's holding the shape of the bed it was printed on, this is a good use case for a thick Raft, if you feel your part can get away with it.The raft would tend to more flat as it got higher. aside from that using some type of bonding agent like Layerneer bed weld or Magigoo in conjunction with (decreased) bed temps might help with your problem. you mentioned you were printing PLA so this shouldn't be to difficult to achieve.

Good Luck

Swiss_Cheese

RE: Large printed parts are not flat even though they don't unstick from bed

Posted by: @swiss_cheese

@justinas

 

I just blew through 2 pages of this thread without reading any of the other answers, so forgive me if this has already been suggested.

 

It's possible, even likely, that your bed is bowing in the middle as the build surface heats up, and since your part is no longer lifting up from the bed it's holding the shape of the bed it was printed on, this is a good use case for a thick Raft, if you feel your part can get away with it.The raft would tend to more flat as it got higher. aside from that using some type of bonding agent like Layerneer bed weld or Magigoo in conjunction with (decreased) bed temps might help with your problem. you mentioned you were printing PLA so this shouldn't be to difficult to achieve.

 

Good Luck

 

Swiss_Cheese

Thanks for that suggestion, I checked the bed during print with a straightedge, but I think it is flat... Nonetheless, I am trying a raft right now, printing a part of this big plate for testing. 2 more hours to go 🙂

RE: Large printed parts are not flat even though they don't unstick from bed

Ok, I had a look at slicer file. 90°C bed temperature is certainly not normal for PLA. It should be possible to print at 60°C just fine, certainly with any PLA filaments I know, Prusament among them. With old PEI plates it can get hard to keep the PLA to stick though even with all the cleaning tricks. That's why I started to use the glue sticks more regularly. Because it worked with that again just fine even with the old plate.

It appears to me you have a more general problem with your first layer or the print sheet.

RE: Large printed parts are not flat even though they don't unstick from bed

Posted by: @thejiral

Ok, I had a look at slicer file. 90°C bed temperature is certainly not normal for PLA. It should be possible to print at 60°C just fine, certainly with any PLA filaments I know, Prusament among them. With old PEI plates it can get hard to keep the PLA to stick though even with all the cleaning tricks. That's why I started to use the glue sticks more regularly. Because it worked with that again just fine even with the old plate.

It appears to me you have a more general problem with your first layer or the print sheet.

I normally print at 60°C with the smooth PEI plate, but when parts get as big as this one, and/or have sharp corners, I bump up the temperature to prevent warping (lifting) during printing. With large parts, it happens both at the corners and sometimes even in the middle of a straight edge. I always use a generous brim for these parts (5-10mm) with elephant foot compensation turned off, but even that doesn't help, as the brim gets torn off the bed by these corners or edges a few hours into the print. Bumping up the temperature to 90°C seems to help. Again, it goes without saying that I always clean my bed with hot water and soap, as well as isopropyl for removing dust, and I never touch the build surface with fingers. My Z height is tuned in perfectly. I am not sure if I can get this any better. Like I said, 60°C works perfectly for small parts, but as they increase, I inevitable have to increase the temperature to compensate for the warping.

RE: Large printed parts are not flat even though they don't unstick from bed

Okay, so my raft test is done - and it appears that I have a flat part! The brim around the raft lifted in one spot, but it was far enough from the part itself to avoid any warping. The surface of the part is definitely not aesthetic, but it is consistent, and most importantly, flat.

Attaching the .3mf for you to check. I used 70°C for the bed. I will attempt to print the full-sized part now on the same raft, and bump the temperature to 75°C just to make sure that raft, or brim, does not come undone.

RE:

How old is your PEI plate? I experienced that my one year old, heavily used, PEI plate started to get pretty lousy at adhesion no matter how I cleaned it. Some say very cautious sanding with superfine sanding paper can restore adhesion again but one can certainly wreck it completely that way too.

What confuses me though is that the glue stick doesn't help because on the bad PEI plate, I can still print wonderfully as long as I am using some glue stick with it.

I never tried rafts with PLA, only once with PETG and there the inherent warping tendency is strong which lead to a rather bad end result. As your problem doesn't seem to be traditional warping (during layer deposition) but the bed temperature gradient maybe the raft does do the trick fairly well indeed. I would try to figure out what your problem with layer adhesion is however. Those things usually don't get better with time.

RE: Large printed parts are not flat even though they don't unstick from bed

Posted by: @thejiral

How old is your PEI plate? I experienced that my one year old, heavily used, PEI plate started to get pretty lousy at adhesion no matter how I cleaned it. Some say very cautious sanding with superfine sanding paper can restore adhesion again but one can certainly wreck it completely that way too.

What confuses me though is that the glue stick doesn't help because on the bad PEI plate, I can still print wonderfully as long as I am using some glue stick with it.

I never tried rafts with PLA, only once with PETG and there the inherent warping tendency is strong which lead to a rather bad end result. As your problem doesn't seem to be traditional warping (during layer deposition) but the bed temperature gradient maybe the raft does do the trick fairly well indeed. I would try to figure out what your problem with layer adhesion is however. Those things usually don't get better with time.

My plate is around 4 months old. I was always very careful with it, never scratched it with a nozzle or anything, it looks really good apart from microscopic scratches that are barely visible.

So anyway, I finished a 12 hour print with the raft, and the results are terrible. The raft adhered to the part a bit too well, tearing off chunks of the first layer upon removal (I was super careful from the point I noticed this, but it didn't help):

And at the same time, in some places the raft didn't adhere enough, creating a very uneven surface, and the part is still concave... 

(The right edge is the edge of the bottom of the part)

So I guess the raft is not the solution either. I need to get PVA glue stick working somehow. The glue stick I have obviously has not a chance in hell. I will attempt to repeat the experiment with other PVA glue stick brands. At some point the expense of all these glue sticks and wasted filament is going to add up to the cost of the Magigoo bottle.... Lol.

RE: Large printed parts are not flat even though they don't unstick from bed

Yeah, that's the kind of result I had with rafts so far. Well, the one time I tried it on a large part (and to make things worse with PETG which warps a bit more than PLA).

I am a bit out of ideas. Get an UHU stic or Kores if you have access to that. For those I know that it can work. (Prusa sells the Kores sticks, so if you have some prusament to order it doesn't cost much extra).

Can you make a close-up picture of how the Prusa first layer calibration looks like (that zigag line etc)?

RE:

I may have a temporary solution for you. I had the same issue printing with PETG. What I did is just use a sanding board that is perfectly flat and much larger than your 3d print and sand away untill i got a flat surface. The only problem is that you may experience discoloration but if you sand progressively low to high to like above 1000 git, and apply vasaline or something simular, you won't even notice any color change. I got this idea after watching this.