Print Height Issues
So I'll start by saying I've loved my MK3 thus far. But I've noticed an issue that taller prints seem to not work as well as I'd expect, and I'm trying to determine if this could be a setup issue or if I may have something else going on with the printer.
My initial setup went without much hiccup, but I did have some difficulty at first getting prints to stay on the smooth PEI sheet. This appeared to be that my Z offset wasn't set low enough, and ultimately I ended up setting it around -750 to get a good adhesion. From there most low prints, such as an exodus toy, bookmarks, and the Prusa logo all worked fine. But when printing some taller components (such as plates that were part of a costume glove, and so up to maybe 100mm tall) I'd consistently run into issues with the printer reporting Y-axis crashes and recovering, which would cause a bit of layer shifting in the finished print.
After tweaking the PIDNA position and running through the calibration process again and following some advice on the forums here to use two sheets of paper with the bed both hot and cold, I was able to get the crashes to pretty much stop, but I still start hearing hearing the head scrape the print once the print gets above say 50mm, sometimes causing the print to get knocked off or other issues.
Which brings me to today's print, this headphone stand. The base printed perfectly, and the stems looked really good as well.... until it reached around 130mm and then it started turning into a bit of a stringy mess.
With this one I'm sure some of the cause could be the height and thinness of the pillars in the model causing some flexing during printing, but at the same time I'm not sure how to ensure that the bottom prints well and clean while also ensuring that upper layers aren't too close to the nozzle as there's been a consistent pattern of it making contact on various prints as the hight increases.
Any ideas/tips/guidance?
Re: Print Height Issues
Those upper layers with the stringing problems look a bit molten. Assuming you're using PLA and that those are the support pillars, you might be running into cooling problems. Layers at that height are going to consist exclusively of the pillars and will print very quickly, thus not cooling sufficiently. Look into slicer options for minimum layer times. You'll typically be able to choose between cooling options including slower print times, increased fan or lifting the extruder away to ensure adequate cooling time.
I'm not sure how you're doing supports based on the provided pics. How are you supporting the headphone support at the top? Is it a separate piece?
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Re: Print Height Issues
The PINDA and first layer issues you may read about are only for adhesion to the build plate.
All subsequent layers are based upon this offset. Second all other layers are based upon the first plus 0.2mm and so on.
Bobstro is most probably correct. The plastic cannot cool before the next layer is placed on those tiny, little layers.
And from what I've read, Bobstro is usually correct.
Re: Print Height Issues
Thank you for the replies.
@bobstro I agree that it looked very molten, though what's odd is that the pillars printed perfectly from the base (which is just shy of 4mm thick) all the way up to where the stringing started. It may not have been clear in the picture, but the result was 138mm of pillars that were perfect until suddenly it started having issues and printed another 30mm of molten pillar, which combined with the other behavior I've noted with audibly hearing the nozzle scratching the prints and on this one where I could see it causing the pillars to wobble as it was printing made me think it was more likely making contact.
Would the cooling theory still explain that behavior? I'm happy to try tweaking layer times, speed and fan if those will help. As far as the support, there is another base piece that sits on top of this one with thicker pillars that these thinner ones fit into, then the headphone support at the top is glued onto the posts.
@peter I mentioned the PINDA and first layer issues for context, as early on I was having issues with adhesion, which were solved by adjusting the PINDA and z-offsets, but I wasn't sure if those may or may not play into the issues I've seen with the nozzle rubbing against prints at higher Z points or not so I included it in case that was an obvious failure on my part.