HIgh Temp Filament 1st Layer Compression (Nozzle Expansion)

Flagship K Series Creality Flagship K2 Plus & CFS
1

Hello,

I have had the K2 Plus for about a month now. For the most part it has been an excellent printer. I did have some issues with z banding on tall parts, and found that loose rail screws were causing that.

THis printer has delivered a trouble free experience with printing PLA. Yet recently I started doing mainly ASA parts for some projects. Since then I have been having 1st layer issues with printing ASA. THe 1st layer is always too close and I have to watch the 1st layer going down and adjust it manually from the screen to get it right.

This is quite annoying, and I have talked with creality about it and have followed their suggestions with no improvement. Their suggestion was to raise the bed temp to printing temp and allow it to sit for 10 minutes, then run the bed leveling. It didn’t change anything.

After thinking about it some I noticed that the bed leveling procedure runs with the nozzle temp at 140C. But ASA prints at 260C. I was curious if maybe the nozzle is expanding when heated to print temp causing the 1st layer to compress.

I ran several tests on this idea. I heated the bed to printing temp of 90C and let it sit for 15 minutes. I then set the nozzle temp to 140C, let it sit for 5 minutes, cleaned it thoroughly and home the printer. After that I jumped into Fluidd and set the nozzle height to .2mm. I used metal feeler gauges and sure enough it was perfect at .2mm height from the bed.

Then without moving anything I heated the nozzle to 260C, which is the printing temp for asa. I let that sit for 5 minutes and then used the feeler gauges to check the clearance. I could not get the same .2mm gauge to fit. So I went down in gauge sizes incrementally until one would fit the same as before, which ended up being a .10mm.

I ran this test several times thinking maybe filament was oozing throwing off the results. To elimante that I changed out the nozzle to a new one and still got the same results. I tested this 6 times with all showing that the nozzle was expanding anywhere from .075 to .125mm when going from 140C to 260C.

So as far as my brain works this would explain why high temps filaments have first layer compression issues. The printer probes the bed and sets z height at a nozzle temp 140C. And when the nozzle temp goes up to 260C the 1st layer is too close.

I am amazed that the nozzle seems to be expanding this much, but it is very long. Maybe is is the hotend body itself expanding, I’m not sure. I’m pretty sure that you shouldn’t probe the bed with the nozzle at 260C because it would probably damage the bed.

So I started setting a .1mm positive z offset (which was the average expansion number I got from my testing) in my slicer for High temp filament prints. This sounds crazy but the printer seems to like it and all the prints I have done since have worked perfectly.

I would like to see if anyone else could test this to verify my results.

Thanks

2

I think you might be right. For me, the nozzle was definitely too low on first layer when printing PC at 270C, but didn’t seem to have trouble with PLA. I tried a first-layer test and played with the Z offset while printing. The highlighted area is an offset of 0, with obvious symptoms of the nozzle being too low. Elsewhere is a z offset of 0.1mm, as you suggested. Perfect.

image
image1330×1447 148 KB

Well, perfect except for the probably unrelated issue of the nozzle inexplicably being way too close around the middle of the bed. Still trying to figure that one out.

3

Cool, I’m glad to see that this isn’t something specific to my printer.

As far a the middle of the your bed being too close, I had a similar issue with my bed at a spot off center toward the rear. I fixed that by bringing the bed to 100c temp for 20 minutes and then running a bed leveling calibration.

I think with the bed being so large that it really takes it some time to kinda settle in on its warpage from the heat. But still there are some instances where it is not perfect, but way better than factory default methods.

I also tried running the chamber up to temp for 20 minutes as well but that didn’t seem to affect it.

4

Looks like I was wrong.
Previously, I heated my bed to 110C and waited a bit before starting calibration, resulting in too much squish. However, I tried again after setting bed=110, chamber=60, and letting it soak at that temperature for about 30 minutes before starting.

The result was very good. There was only one region of the bed which had slight over-extrusion.

image
image1835×1353 202 KB

I haven’t isolated what the cause is yet. I wonder if it is the chamber heater - I print with a target chamber temperature of 60C, but I’ve noticed that the chamber heater doesn’t turn on until after the print starts. Need to do more testing.

5

If you dont send a print to the K2 you can activate the chamber pre print, but it must be 41 degrees or over.

6

I answered my comment to a similar question here: Is Bed Leveling Actually Working on the Creality K2