What might be causing this in my 3D printed parts, and how can I fix it?

Mostly Printed CNC - MPCNC Advice
1

I have two 3D printers, a CR-10 and a Monoprice Select Mini V2. I bought the CR-10 new, and I bought the Monoprice used, and it came with 2 mostly full rolls of PLA (not stored in bags).

On the weekend I started printing using Monoprice (and the filament that came with it) because I wanted to get it up and running for my kids to use. I printed the feet, the bottoms+tops+locks+spacers. I printed using the % infill from the instructions, the cubic infill pattern with the “draft” profile (.2625 layer height) and 35mm print speed (as per an older “parts” document) at 190 degrees nozzle and 60 degrees bed. I lowered the temperature to 190 degrees to reduce stringing.

However when I take a closer look at the parts that I printed I see little gaps here and there between the layers. I’ve attached two photos.

What might be causing this? I just started printing another part on the Monoprice, but this time using 205 degrees nozzle instead of 190, and so far the part doesn’t seem to have gaps like this, but it isn’t done printing yet.

I’ve switched over to my CR-10 for the rest of the parts, but I have a couple of questions:

  1. What might be causing this on the Monoprice? Is my guess that it is temperature related correct? (I want to get the Monoprice dialed in for my kids to use; they are 9 and 10 and they aren't going to be troubleshooting any problems that arise)
  2. Can I use these parts (and replace them *if* they break) or should I just spend the time and reprint all these parts? (It isn't the couple of dollars of plastic that I'm agonizing over, but the time it took to print these parts - now that I've finally starting printing everything I want to keep up the momentum and put it together as soon as possible and get it running.)
  3. Has anyone tried annealing their PLA parts? Might that help in this case, or would the dimensional changes make the parts not fit correctly?

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2

A few things can cause that. You can print a temp tower to dial things in. Any PLA I have now prints at 205-215 now, For years it was 195 then all of the sudden every brand jumped 10-15 degrees. If you print a temp tower you will know.

Could also be a clogged nozzle.

Reprint them for sure, don’t waste your time annealing (and getting the right initially scaled print to compensate…just hype).

3

Agree on the temperature, usually, if you have layer adhesion issues, increasing the temp helps, since you’re already printing pretty slow. I have matter hackers build PLA, and have pretty crappy layer adhesion at above .2 (I usually print at .25), unless I added another 10 degrees from my normal printing temperature.

4

Could be several things:

-Temp too low, try to print at 215 degree C, it’s usually what gives the best layer adhesion/print quality ratio. also check that the temperature your screen display is accurate, if you can.

-Fan speed too high, if you have a part cooling fan you can decrease its speed, to avoid cooling the plastic too fast

-Partial clog or extruder skipping steps/sliding, your nozzle could have some temporary clogs. Check if your temperature is stable, otherwise your heating cartridge or PID setting might be faulty. Check also that the extruder motor doesn’t skip steps or that the filament isn’t sliding over the extruder pusher wheel. In which case, tighten the extruder spring and/or adjust the current output from your drivers.

-Poor nozzle heatsink cooling, the plastic will melt in the heatsink, resulting in a clog. Sometimes this clog will solve by itself (but some layers will not be printed well), and sometimes it will clog entirely.

The only way for you to make sure of what is happening would be to stare at the machine while printing the entire time. I often do that and it helps a lot in troubleshooting (but it is a bit boring and time consuming).

Also, your printing speed is super low, once you’ll find the correct settings you can bump it way higher.

Try not to change your temperature settings to lower stringing. It is effective but this is a bad habit. Temperature should remain fixed only for best layer adhesion/best visual outcome ratio. Stringing can be fixed only with retract/prime/sweep functions, you need to find the sweet spot for retraction distance, retraction speed, sweep lenght, acceleration, z lift, and all that stuff. It will work at some point, you seem to print with a .4mm nozzle so it won’t be hard to find a good setup.

In any case, you should scrap those parts, they are useless.

5

Hi

Another thought that came too mind, is your printer in a case? Or is it open?

If it is not in a case then it looks to me be be thermal shock, basically if the printer is not in a case the air currents can cool the plastic far too quickly and does not allow the layers to adhere… I have found it very difficult to print with an open printer. Both mine are in cases and print very well

 

regards

6

Before you scrap those parts, I would try a little destructive testing. I have seen things like that on some of my printed parts and when it’s extreme, delamination can occur. But, when it looks like what you’ve pictured, I’ve often found that the parts are still structurally sound. It sure isn’t optimum and if you demand perfection, do what you will. But, I’m more of a functional kind of mindset and if the part is structurally sound, I can put up with a cosmetic defect. Opinions vary, of course. But, I would try to tear it apart first with a couple of pairs of pliers or hit it with a hammer to see if it will delaminate.

ETA: I just looked at two identical parts with the same defect that you show in your pictures. One thing that I’ve never noticed before and that I find extremely interesting is that they look exactly alike and are in exactly the same place on both parts. I’m not sure what this means, at this point. It could be anything, really. A mechanical issue on an axis perhaps, an artifact from the slicer, etc. But, I do know that these parts are mechanically sound. A third one is printing out right now and it will be interesting to see if it is on that one, as well.