New to the Process: Calibrating the Machine

Point taken (no pun intended).

I’ve kept it between 190 and 205. Nothing higher. Typically I do 4 print runs of the same gcode at 190, 195, 200, and 205 to get a good idea of which temperature is working best. And I am using Luban, but with a custom copy of the Normal Print setting, modified for 1mm/60mms retraction and 0.5 Z-hop. The layer depth is set to .15mm after an initial layer height of .3mm.

Again, I’m using Luban, but that is mainly because it came with the machine and I haven’t the budget for a new program, and the bureaucratic hassle of getting a new piece of software added to the computers in a public school is a nightmare (it took me almost two years to get them to add Adobe Creative Cloud rather than continue using Creative Suite 6). So let’s assume I’m stuck with that for the moment.

I agree. I started to print out a set of miniatures (I plan to use these for my Game Design class), widely spaced apart at 205 degrees, but immediately got some serious webbing issues that were not present in the previous retraction test prints:

I tried to adjust the nozzle temperature down to 195 during the process, to try and correct for that, but the nozzle never cooled down to more than 204, so on the fly adjustments don’t really work.

The sad thing is, before I updated the firmware to make up for the extraction error issue, I got one good print out of the machine (this was a few weeks ago):

As you can see, no spikes, everything printed with a clean separation, and minimal webbing between the antlers (which I would expect). Once I updated, however, everything started getting spikey, and the best I’ve been able to do since then is to dial it back it to the point where it looks like I have a machine full of spiders.

I’m looking at other colors of filament as we speak.

As an aside, I am totally new to this process, as I have said, and the folks on this forum have been fantastic. Much obliged to all of you for helping me through this…

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It’s prudent to be mindful of assumptions being made.

Unless you’ve verified the thermistor is reporting the temperature accurately, that’s an assumption. The exact number is not important, and a temp tower (like the one from Teaching Tech) is necessary to find out optimal temps for your machine.

On my machine 205 is the minimum acceptable temperature for the layers to fuse while printing. On yours it appears the model is sagging from the heat. Indeed, this has wider considerations where some models may need different cooling or different nozzle temperatures to have better layer adhesion and strength or less sagging or better bridging, etc.

From the perspective of ‘continuous improvement’ your examples of ‘good prints’ seems to have several aspects that can be improved. I’d be interested in which model the bottom middle print is - some of those surface pocks seem plausibly in the model, but if not would be indicative of serious slicer or firmware issues.

Regarding the stringing - have you tried replacing the hotend? Rarely, but sometimes, a burr or machining defect in the nozzle can result in unusually bad stringing.

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@brent113 has made some good points, and there have been some new updates, which I discuss below.

Ok, from what I see here, I think I have some good news. First off, a firmware update was just released, and it corrects many of the issues that the previous update created. You should upgrade the firmware ASAP, before proceeding. After reviewing the latest pictures and information that you provided, along with something that I just learned about the new 3D Printer Module, we first need to determine which 3D Printer Module it is that you have. Snapmaker apparently started shipping the new 3D Printer Modules recently, and there is a design flaw in the part cooling of the new 3D Printer Modules.

They apparently changed the part cooling air flow, which results in the right side not being cooled. On the bottom of the 3D Printer Module there is the nozzle in the middle, a long cooling vent on the left, and 2 blocks on the right. The larger front block on the right is either a solid block, or a vent. The original parts have a slit for cooling, while the new parts are just a solid block. Which do you have? This will determine which way we need to proceed.

You might want to try one more print with Z-hop configured in Luban. This might make a big difference, and otherwise allow you to move forward. We’re here to help, and it looks like we’re very close to a conclusion. I fully understand the limitations that you need to work with in a school environment, and hopefully both you are your students will fully operational very soon.

All this being said, Luban will probably be fine for your environment. However, some more good news is that Ultimaker Cura and PrusaSlicer are free for everyone to use. Read the licenses and see if they work for your environment. Neither require licensing fees, and there may be special offerings for educational environments. I would recommend that you evaluate both of them on the computer that you are using, and to not install them on the computers that the students are using at this time.

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I’ll put that on my list of test prints.

I’m trying to knock out issues one at a time, while trying to understand the principles behind the various settings. Once I get the stringing reduced or eliminated, I’ll definitely look at those.

That would be a last resort (out of budget for the year), but if nothing else works, I can try that.

I updated the firmware when 12.0 came out. That’s when my prints started getting hairy. As for the module, both sides have a slit/vent. It’s also very dirty under there, with some sort of splashback/splatter on the area around the nozzle. How do you clean that?

Z-Hop has been configured to 0.5mm on the previous prints.

That is helpful! Right now, I’m running the printer from my machine only, so one is all I need, and one free bit of software is much easier for me to swing.

I guess I had a different thought: I usually troubleshoot by starting with the settings that are tied to physical things, the artifacts I was seeing are indicative of issues with that.

Once the machine is physically doing what it’s commanded to, then one can move up to the next layer of abstraction and begin turning other knobs in the software.

The fundamentals are extruder steps/mm and flow multiplier.

If there are any issues with those, sometimes even endless tweaking will not eliminate issues.

It should be one of the first things you try. There’s one in the toolbox that came with the machine. It’s free and takes about 2 minutes to do.

If having replacement Snapmaker hotends on hand is cost prohibitive, having just spare nozzles on hand is fine too, and they cost in the ballpark of 25 cents each. Changing one takes just a few minutes.
image

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I thought that was what I was doing. I updated the firmware to fix the extraction error, modified the steps/mm, and tried various temperature settings, as many folks have suggested. I’m pretty sure that I’ve now eliminated Retraction as an issue, as I no longer get thick spikes and strands, only the webbing.

So the question is, where to go from now. You mentioned flow multiplier, and I can see a Flow Percentage in the Material settings (which is currently set at 100%). Tell me more about that.

I totally forgot about the spare, until the moment you mentioned it here. So that I can do. And it looks like I can get the hot end replacement kit from Amazon, so that’s doable (we are restricted to specific vendors when we purchase, which is why I had to wait to for the SM2.0 to arrive on Amazon before I could purchase it, costing me several hundred extra dollars).

Are those MK.8 nozzles compatible with SM2.0? And how do you replace just the end of the piece?

With a few exceptions MK8 nozzles are compatible. You may need to recalibrate after if the Z height changes due to length differences between nozzles.

With a crescent wrench or similar to apply a holding torque to the heat block, and a 1/4" hex driver to unscrew the nozzle. Prusa has a good write up that is applicable here: Prusa Knowledge Base

I don’t know that you aren’t - just suggesting that the seemingly unrelated issue of pocks and artifacts on your other prints may not be unrelated at all. All of these settings are intertwined, with some surprising connections.

If E-steps is the 2D calibration (length of filament) then Flow is the 3D volume. Once steps per mm is correct so that the machine is extruding the correct commanded length then the slicer needs to know how to convert between linear filament and volumetric filament. The flow multiplier is the software ‘knob’ that can be turned to compensate for any deviation between an ‘ideal’ and ‘real world’ conversion that results in under or over extrusion.

The classic way to set it is to print a hollow box with single extrusion thickness walls. Typically 3D printers print an extrusion width of 100% to 120% of the nozzle width - for a 0.4mm nozzle good prints happen around 0.48mm width. This is because of the ideal extrusion shape of obround with enough flat area on top and bottom to adhere to the adjacent layers.

The calibration tool here will help with this test: https://teachingtechyt.github.io/calibration.html#flow. I would recommend targeting a wall thickness of 0.48mm. (Turns out Luban can’t do this)

This test I would consider “done” when your measured wall thickness is within +/-0.03mm or so. It will be impossible to dial in 100% accurately at this time, as there are likely other issues that have not yet been calibrated, for instance, linear advance which can put a small blob at the start of segments affecting the width.

Flow is tied to the type of filament, PLA will likely have a different flow multiplier than ABS, TPU, etc.

The latest version of firmware is version 1.12.1, which was just released on April 27, 2021. I’m pretty sure that you have 1.12.0, which is the previous bugged version. BTW, you can always go back to a prior build by installing it from a thumb drive, unless otherwise stated. You have the original 3D Printing Module, which is good. There isn’t very much that you can do to keep it clean. Isopropyl alcohol can be used, as well as anything else that does not damage plastic (acetone and denatured alcohol melt/damage plactic). There are also clear paints that are designed for hot ends to prevent filament from sticking in the first place.

All this being said, I have some mixed news. It is very likely that you have a bad batch of filament, where the chemistry is not balanced properly. The long runs don’t look to bad, but they are slightly irregular when you take a very close look at them. The filament that you are using has an issue with very short burst runs, which is something that the twin tower test doesn’t pick up, and is why I stated that retraction tests are very tricky. What we also need are tests for bad or poor filaments, but that can also be subjective, so it’s something that you’ll learn over time.

The problem with this filament is that very short runs cause the filament to be in the nozzle for a longer period of time, and it is overheating due to the chemical composition. That is what is causing the stringing. A good PLA filament won’t overheat like this. This is an issue that is mostly seen with PETG, as it very finely skates this imbalance edge to obtain it’s characteristics. If you have a small fan that you can direct toward the printing area, it might helps with your prints while you use this filament.

How to move forward:
I see that @brent113 discussed changing the flow, but have you calibrated the extruder? The Teaching Tech site also has a tab for calibrating the extruder, which is probably the very first thing that anyone should do when calibrating their printer. I would do that before playing with the flow rates. I’m going to differ with what @brent113 is saying, and have you start with 0.4mm wall thickness instead of 0.48mm, as Luban is hardcoded for 0.4mm and that can’t be changed in the UI.

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Great stuff, gentlemen! I appreciate it!

I’m going to go implement what you’ve told me as soon as I can. Unfortunately, state testing is upon us in the public schools once again, and I have to divert my attention to that for the next week and a half, but as soon as that’s over, it’s back to The Machine.

I’ll be back to let you know how it turns out, but until then, I appreciate your kindness and patience in helping not only me, but the kids who will benefit from this tech.

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