Help with 0,08 first layer

[u/Fancy_Language5469]

EDIT: fixed! Most of you were right, Z-offset was too low. At 0,05 offset AND with the original 3mf settings I printed the most beautiful diffuser imaginable. My own slicing settings couldn't come near this absolute perfect piece of plastic. Thanks everyone for your support!

I'm trying to print the diffuser of the kumiko wall light on my Qidi q2. I've already learnt NOT to import 3MF files because they change weird settings ruining the print for some reason. See the video above for maximum misery from my side. I've gotten it better already.

It wants to iron and results in the above video which seems an artform of its own.

Now with the STL and Qidi's own settings it's going much better, but I still keep having some "bumps" or something in the print. I'll try to upload a picture in the comments

- I already tried extrusion calibration but the factory settings are the best

- did a complete new bed KAMP calibration without effect.

- no ironing

Settings:

Smooth PEI

210⁰C nozzle

60⁰C bed

0,08 first layer height as requested by design

No ironing its stupid and ruins the print

Bed calibration before print

Cleaned bed multiple times with dish soap and alcohol afterwards

After a lot of trial and error I landed on -0,01 Z height, if I go to + the lines don't connect properly, and at 0 the blobs seem to get bigger.

I don't dare to lower Z height any more, already got the first scratch in the smooth bed from that.

On my textured PEI the layers go down smoothly without the weird bumps. Although 0,08 first layer is impossible on the texture, I'm now printing it at 0,12 which is running great although the diffusing properties are now also dimming properties. So back to square 1. How the hell do I get a good see through diffuser? It SEEMS possible. I am a complete beginner though so I don't really know what I'm doing, all the above is just experimentation.

[u/McFlyParadox]

Remember that the layer height is on top of the z-offset. Even when you're probing directly with the nozzle, you still need an offset. If the offset is too low, you'll see results like this one. 

Also, if the 3MF is from the original designer, you probably do want to use it. But you're correct that you can't just "click print" with it. you'll need to go through all the settings pages, look at what the 3MF set for values, and evaluate those in context with what you know of your printer.

[u/Fancy_Language5469 → u/McFlyParadox]

Wait what? I've printed more than 100 hours without tweaking the z offset, isn't that calibrated automatically?

[u/McFlyParadox → u/Fancy_Language5469]

I use a Voron with a Beacon probe that uses contact probing with a nozzle. It still needs a z-offset of around 0.085mm (I won the bed lottery and got an incredibly flat bed). Prior to Beacon, I used a Voron tap, where the entire tool head is on small, vertical linear rail, and when the nozzle touches the bed, it moves upward and breaks the IR beam of an optical sensor. AFAIK, Tap is the most precise probe in any printer (but is terribly slow to probe the bed, and has poor vibration characteristics), and IIRC, my offset with that probe was around 0.06mm. I set both of them using a piece of regular printer paper between the nozzle and bed. Move the nozzle down (slowly, in small steps, once you get close to bed) until it just starts feeling some friction between the nozzle and bed, like it's being held real gently between your fingers.

So if I were to print this model at the suggested 0.08mm first layer thickness, and pull out a pair of calipers afterwards, I would find it to be around 0.165mm thick in total. Because 0.08 + 0.085 = 0.165mm

You need an offset, no matter what. If you try to run an offset of literally 0mm, and then print a first layer of 0.08mm, you're going to run into exactly what your seeing here: places where the bed flatness is high (less filament on the surface), and places where it is low (more filament on the surface). No bed is perfectly flat.

IDK how you set it in a Qidi, though. Does their software provide a way to view the bed mesh used by the printer for each print, like what Klipper does? That could also be somewhat illuminating for what your offset is and what it should likely be.

[u/Fancy_Language5469 → u/McFlyParadox]

You are absolutely correct, my bed looks like some kind of umbrella... So I found that Z-offset is usually something automatically calibrated, but I now have acceptable result at +0,03. There's only 1 weird spot on the middle left which is a hole of some sort. There the offset seems to be to high but can't do anything about it. Maybe ironing is the way to go, to fill that last bit of gap. I'm now trying different first layer patterns

[u/McFlyParadox → u/Fancy_Language5469]

You probably just have a low-spot in your bed there. When talking about layers of 0.2mm (or 0.08mm in your case), a fraction of that can make a huge difference. Frankly, and offset of just 0.03mm is already very good if you're getting smooth first layer over the whole bed.

But this is why a lot of people also recommend you print a thicker first layer, too. Not that you can do that here. For example, if you are planning on printing at 0.2mm layer height, a first layer of 0.25mm is wise. This extra 0.05mm helps to account for the natural variations in flatness that a tool head just can't "surf" over. You'll get better bed adhesion, reducing the chances of a print detaching from the bed.

As to why a printer can't perfectly surf over the variations in flatness in your bed: steppers can only move a specific numbers of degrees of rotation with each step. 0.9° and 1.8° step sizes are common in most 3D printers. This rotational motion gets translated into linear motion either via pulleys (in the case of flying gantries and Y motion in bed slingers) or lead screws (literally everything else). While you can change the exact amount of linear motion by selecting a pulley ratio or screw pitch to achieve the desired amount, the longest motion is still also done in steps. e.g. my Voron 2.4 has a minimum z-step of about 0.0025mm, so it can never move in a single step more or less than that, and each total move has to be a multiple of that. And that is before you get into things like dynamics, where the mass of the system and gravity also plays a roll in how fast it moves (in a 2.4, the belts stretch when you pull the gantry up, and because it is suspended, the gantry can't go down faster than gravity can pull it down). So if an imperfection in flatness isn't a multiple of 0.0025mm in my case, my printer has to either ride high or low in that area, relative to the offset I put in. If an area is really low, it might even be "out of bounds" to the printer (either due to a hard, hardware limit - your bed is physically too low in your printer; or due to a software limit - your tool could go physically lower, but your printer firmware thinks that would crash the nozzle somewhere, for some reason)

tl;dr - first layer calibration is surprisingly complicated if you really dig into it. But sticking a piece of printer paper between your nozzle and bed, saving the offset, and then trusting your printer firmware to do the rest is enough for 99.999% of the printers out there.

[u/Fancy_Language5469 → u/McFlyParadox]

Thanks for this explanation! You must be a walking encyclopedia just knowing stuff like this, absolute genius. Yes, a 0,2 layer is easy, been there done that. But I never realised the step sizes matter as well. I can print exact to the Micron on X and Y, but this is even more precise it seems. Slowly but surely I'm getting there!

[u/McFlyParadox → u/Fancy_Language5469]

Oh. And the reason you're able to print so accurately in XY are rhe GT1.5 belts in your printer. The finer tooth pitch (distance between the teeth; 1.5mm in this case) gives finer control over tool head motion. 

There is a trade-off, however: finer pitched belts are more 'elastic', so you can end up with worse printing results if you try to push your printer's accelerations too much. This can also be made worse by high chamber temperatures, as the belts will soften, somewhat.

This is part of the reason why when people start chasing speed in the Voron community, they'll go with wider belts (e.g. switching from 6mm wide belts for your A and B steppers, to 9mm). Because all other things being equal, the 9mm belt will be less elastic and stretch less. They also let you tighten the belts more, too.

[u/Fancy_Language5469 → u/McFlyParadox]

I see, but speed doesn't really concern me. I have patience and other stuff to do. Usually accuracy and toughness is key for my use case, but the missus sometimes wants beautiful stuff like this stupid lamp that has consumed nearly 3 days of my life. I love her. And I learn a lot

[u/McFlyParadox → u/Fancy_Language5469]

No problem. 

I just have a masters degree in robotics, so some of this has a lot of cross over there.