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Nozzle hitting print bed even though completely leveled?


#1

Hi, I am new here and very new to 3d printing. My husband and I built an Alunar M508 Prusa i3 and we are having all kinds of trouble. Long story short, we have made sure everything is square, leveled the bed manually, and when we start a print the nozzle starts out fine then digs into the bed. We are going with a cold bed for now, using crepe tape, and we are using PLA at 200C. We used a feeler gauge to level the bed, have reinstalled the firmware (martin), and easily have 100 hours into this.

We are both mechanically and computer inclined, he is an electrician and mechanic and I am a 20 year IT veteran and network engineer, and we are both about as frustrated as we can get. Any help would be very, very appreciated before we chuck the whole thing into the lake we live on, literally.

EDIT: We were using a file from Pinshape when this happened. We decided to run a print from the test prints that came with the printer and the problem did not occur. Is this potentially a slicing issue? I used Cura 15.04 to slice.

EDIT TWO: A few minutes into the test print I hear blue language from hubby, The print started to glob, He isists that .1mm is too close, and I said that is the recommendation but he insists on .2mm bed leveling. Is 2mm causing us trouble too? We have been using .2mm from the start because he is sometimes rather stubborn.


#2

First, let’s clarify what level means, because it’s different than the concept of “level” when describing a floor in a house or laying out forms for pouring cement, etc. Those applications use a leveling device (ex. bubble level) to measure whether the surface is tangent (or perpendicular) to the straight line emanating from the center of gravity for Earth to the object being measured. When it comes to 3D printers, “level” means that when the build platform is as close as it can be to the nozzle, the nozzle needs to be the exact same distance away at every point on the build platform. In other words, a properly leveled print surface probably won’t be level when measured with a bubble level. You probably already knew that, but I wanted to make sure you understood the difference in meaning.

Now that we have that defined, the distance from the print bed is most often set at about 50-80% of the layer height. This causes the first layer to be “squished” onto the build plate, enhancing adhesion. So, for example, if you are doing a layer height of 0.2mm, you would want the distance between the build plate and the nozzle to be 0.1mm. If you are printing at 0.1mm, set it to 0.06-0.07mm. The smaller the distance, the more the filament will be squished into the surface. If you set it too low, it can scrape the bed leaving no filament at all. If you set it too high, the filament won’t stick to the bed. Instead, it fill form a constantly growing blob of plastic on the nozzle which gets dragged around on the print surface until you abort the print. I print a lot at 0.1mm layer height, because I love the smoother surface. In my case, I slide a 0.07mm feeler gauge under the nozzle. When it resists being dragged under the nozzle, I consider it set at the right height.

The trick is to make sure the build platform starts out positioned at the mechanical limit closest to touching the nozzle before you do the measuring. On machines where the build platform moves down as it prints every layer, This means it needs to be raised as far as it can go. On machines there the print head moves up as it prints each layer, which I believe is the case for your Prusa, you need to have the print head as low as it will go. If it hits the build plate before it hits the lower limit, you need to move the print platform down until it is barely touching or move the lower Z limit switch up a little, so the print head can’t travel so low. Then, just move the print head around over the print platform and check the space. It will always vary a little, because no print bed is perfectly flat. Just get it as close to the proper height as you can.

I hope this helps.


#3

Thank you BillDem, I think I do understand the leveling term in this context, and I thank you for the clarification. I need to convince hubby to go to .1mm for nozzle height. On the Prusa the bed does not rise or lower except by manually turning the screws, and I’m thinking maybe the limit switch could be an issue.

Last night we did another print of the same object that we’ve been using to test with, using supports (it is the Magic Puff Dragon here on Pinshape), and all went well until about midway, when you could see a distinct shift, but we let it continue. It didn’t actually finish the object though. It printed only part of the top of the head then said it was 100% complete and stopped. I am at work today, but later I’ll post pictures of it. I think that may be a slicing issue??

The whole situation is weird because we think we’re leveled and then the nozzle crashes into the bed, then we re-level to the same specs and it works fine. I did notice last night when the print “finished” that one of the hex screws for the extruder motor had come very loose and I think that may have also had a negative impact. It has been pretty frustrating over all.


#4

First of all welcome to 3D printing! It has it’s joys and frustrations, and this is definitely one of them: getting the first layer flawless. The nice thing is, once you get this figured out, it makes it a lot easier.

I will tell you one thing for certain, especially when you are starting out. It is usually easy to assume a problem with the slicer, or the filament, but 100% of the time my problems have never actually been from either of these. You can got to https://tools3d.azurewebsites.net just in case, and repair the STL just in case.

When describing the problem, it is very important to know the exact set of events which are happening. “Starting to glob” is not going to be descriptive enough for me to diagnose, but I can make a few guesses to help you approach this algorithmically.

Is the nozzle too close or too far?
This is a critical question you need to answer. Look at visual guides for what first layers should look like, for example HERE

You can usually tell if you watch carefully. A nozzle that is too close can scrape against the bed, causing no extrusion, and damaging the bed. This will both jam the nozzle and cause the filament to grind into the knurled bolt (which you should clean out just in case), and cause worse complications later on. If the plastic is extruding, but squeezing out the sides too much, this will create poor adhesion. If the nozzle is too far, the plastic will not hit the bed, causing poor adhesion.

Poor adhesion causes the print to come loose and fail. Your perfect first layer will have a very distinct look to the plastic bead, and you will have to develop an eye for this, since 3D printer z-axis can be imprecise and need constant adjusting. You can not only level your bed properly, but adjust your initial z-height which is a critical process. I had run 3 of the same printer model, and each one needed a different initial z-height to get a perfect first layer.

The other factor that will create poor adhesion is if the plastic is too cool on the first layer. I typically print closer to 205 or 210 sometimes. Cura should have advanced settings that allow you to adjust the temperature and layer height for the first layer only.

Another factor is if the bed is too cool or too hot. This heavily depends on the printer surface, but for PLA I use 40-50 C, but I have PEI sheet which allows me to print cooler and stick. You may need higher for glass or different surfaces.

Most notably: 0.3 mm nozzle is a very tight aperature and 0.1 mm layer height is very fine . This is a more advanced print you are attempting as a beginner, in my opinion. I do an initial layer height of 0.425, but I have a different printer and a 0.5mm nozzle. For you, if nozzle swapping isn’t possible, one option is to slow the print down, which helps solve problems for a variety of issues. Another option is to increase the layer height to more like 0.3mm… I would highly recommend starting with larger layer widths as a beginner. Keep in mind when you change the layer height, you may have to adjust the initial layer settings, or the initial z height.

If you are using PLA, a trick a lot of people use is to cure the nozzle with oil. You can look that hack up as well. I myself during long prints will oil at certain times if I am going to be away for many hours, and I’ve completed long 30+ hour prints.

Remember, try changing one thing at a time. If it fails, try and reset and adjust a different thing, or the same thing to a further degree. If you change ten things and fix the issue, you will never know which on actually caused the issue, and may have created 9 additional problems later on.


#5

Yes, MDS is right. The start of the journey is definitely rough. A 3D printer is an intricate machine which needs everything to be precisely aligned, tightened, and tuned to get the best results. That makes the initial learning curve pretty painful. But, when you get it right, it offers you the bliss of a creator as a reward. There is an amazing amount of satisfaction in turning your ideas into tangible reality.

Anyway, regarding the head cutoff. One thing to check is to make sure the height of the model you are printing is below the maximum height your printer allows. Ideally you want it to be a bit below that maximum height. In addition, the slicer needs to know that same upper height limit. If the printer, model, and slicer height limits don’t match up, you will get strange results, like the top of your model being cut off by the slicer.

Regarding the strange shift to one side. That can happen when your belts aren’t tight enough. It can also happen if the print head catches on something while moving. Another cause is the motor on your X or Y axis vibrating loose, which consequently results in the belts being loose. Since you already found one loose nut, I would go over the whole machine looking for nuts or bolts that have vibrated loose. Use a drop or two of Loctite (blue is the one you want, if I remember correctly) then tighten every nut, and bolt. Make sure the belts are pulled VERY tight and Loctite those bolts, too. You can tell when a belt is tight enough because you can produce a clean musical tone by plucking it like a guitar string. If it sounds flabby or sloppy, it’s still too loose. Check that all of your end stop switches are positioned correctly to restrict the outer limits of the print head movement within the correct dimensions of your build area.

I can still remember when I first figured out that many of my early struggles were due to a variety of nuts vibrating loose on the first 3D printer kit I bought. My reaction was to replace every nut that I could with nylock nuts and then use a drop of Loctite on top of that. It fixed about 60% of my problems permanently. Tightening my belts a lot helped fix another 20% of my issues. Experimenting to find a filament and slicer settings which worked better with my machine fixed the rest.

Also, get in the habit of visiting YouTube and watching 3D printing videos that show you how to fix a variety of problems in your 3D prints. You will be amazed at the insane amount of information available from other users who documented what they discovered when fixing specific 3D printing issues. You may even find a few using your precise model of printer.

Best of luck! Welcome to 3D printing! I hope the rest of your journey goes more smoothly.


#6

Thank you so much BillDem, we finally got it calibrated correctly and I’m having a ball using it. Now I’m ready to go to a dual extruder, and hoping I can!


#7

Hello All,

I know this is an old topic but I just got a creality ender 3 and have printed multiple things with no issue at all. Recently in my last print I have had the nozzle starting to run into the print. What will happen is it will print the 1-5 layers fine then it seems like the Z axis stops stepping and starts to squish the extruded PLA on to the build and no building the correct size layers. All my setting are correct- my software has not changed. I have successfully printed multiple things perfectly and then out of no where this started happening. I even went back and test printed items I have successfully printed in the past and the same issue occurs. Any helper ideas would be great- thanks!