ABS does't stick and curls - Prusa mk2S  

Re: ABS does't stick and curls - Prusa mk2S

My questions:
Do I need advanced settings (left / right / front / rear) to fix this issue?
More general - why do these advanced settings are needed if the Prusa probes the bed (accurately) at the start of a print?
Should I be worried about the temperature differenced in my heatbed?
Any other suggestion for something I can try?

It is very difficult to get good bed level compensation with only LRFB settings. I really expect to see Prusa adopt Hyperfine bed levelling as standard in some future release of the software.

The PINDA probe checks to ensure it finds the bed within a certain tolerance range of the saved values and as long as it does it proceeds with the print. If any one of the measured points is outside the allowed tolerance it will fail, but it does not update with the new values found each time it probes, it continues to use the original saved values.

No, the temperature difference is normal.

Something to try now? Slow down the print and increase bed temperature by 5 degrees for the first layer.

Persevere, it is worth it.

Re: ABS does't stick and curls - Prusa mk2S

Thanks for the reply.

It is very difficult to get good bed level compensation with only LRFB settings...
I thought the whole notion of 9 point calibration (either the long XYZ process or the print startup flow) was so that there's no need for manual calibration. The long calibration process should identify the ±50 microns difference caused by the bed not being perfectly straight or aligned.

If that's not the case, what are the results of the calibration, and how are they being used in every print? Also, if the print start "fast-calibration" is nothing but a pre-print rough check (not that it's not important), this means the settings are totally static, and that goes against Prusa's publications. I guess I'm asking for official Prusa details about how calibration and advanced bed leveling coexist and why.

Slow down the print and increase bed temperature by 5 degrees for the first layer.
Actually, that was exactly how I printed the first ABS parts that got wrapped.

Note: after tweaking LRFB settings and lowering the nozzle so the first layer is really squashed (and I get a bit of an elephant foot), I get very good adhesion (until proven otherwise). I might try to raise the nozzle up 10 microns (or more), as long as I get good adhesion.

Re: ABS does't stick and curls - Prusa mk2S

Same here.

I have just spent two days with the same problems. I have been using PLA/PETG since I got my machine 3 months ago, and started using ABS this weekend. I started with a very clean PEI bed, nothing would stick not even the skirt or brim. I did notice that the strip laid at the front left corner stuck quite well to the bed, but didn't make much of it at the time.

I mixed up some ABS Juice, 4g of filament to 50ml of Acetone. Then I was at least getting the prints to stay in place for a while, although the first layer quality was very poor, the rest of the print was pretty good, until the print became detached. I started to adjust the bed temperature and first layer temp with no better results.

Then I started thinking about the strip laid down at the front, and noticed that it was printed at 0.15mm layer thickness. This led me to start looking at the first layer Z height. I picked a 20mm diameter, 5mm high, hollow cylinder to print, and started to reduce the Z height by 25um at the start of each print. I started at -475um which the optimal height I use for PLA on my printer, set using the V2 Calibration gcode file when I first got the Mk2S kit. At 550um I stopped using ABS Juice as the prints became very difficult to remove. At -575um and -600um I got a good first layer and the print stayed stuck to the bed very well, even without Juice. I tried -625um and the first layer quality had gone down and it came away from the bed very easily. So in future I will be running the Z height at, -590um for my ABS which is 115um lower than my optimal PLA Z height.

The attached picture shows the difference in first layer quality at different Z heights. The cylinders at the right have a 1mm fillet at the bed end. I read somewhere that PETG stays stuck to the bed better with a fillet, though whether the same is true of ABS i don't know.

Re: ABS does't stick and curls - Prusa mk2S

As a follow on from my post yesterday, I set the Z height to -590um, and set to work printing the parts I needed in ABS.

I started printing at 11:15 this morning. I printed straight onto the PEI bed of my Mk2S, I did not use ABS Juice, and I forgot to wipe the bed down with Isopropyl Alcohol before I started. Each print takes about 2 hours 35 minutes. I was hoping to get 2 good prints by 22:30 this evening. As it happens I got three excellent prints, no failures and was finished by 20:00. Each print is clean and stuck to the PEI very well, in fact I was able to remove almost all of the surrounding support material without any of the prints coming loose.

Material Used:
PrimaValue ABS Dark Grey
1st Layer Extruder at 235 C, subsequent layers at 225 C
1st Layer Bed Temp at 100 C, subsequent layers at 100 C

I decided to adjusted the bed temp to 105 C for the 3rd print, since I already had the 2 prints I needed, but I could detect no change in bed adhesion or 1st layer print quality.

Final Thoughts
I realise it is still to early to make any kind of conclusions, but I think that more people need to be looking at the Z height setting for each material they are using. I notice that the Z height calibration in software version 3.1 is only set up for PLA, and so is the earlier V2 Calibration GCODE file. If you want to use the V2 Calibration GCODE file with a material other than PRUSA PLA, then you will probably need to change the temperature setting in the GCODE file in lines 2 to 5, as follows:

M107
M104 S235 ; Set Extruder Temperature Sxxx
M140 S100 ; Set Bed Temperature (Fast) Sxxx
M190 S100 ; Wait for Bed Temperature to Reach Target Temperature Sxxx
M109 S235 ; Set Extruder Temperature and Wait Sxxx

The GCODE file can be easily edited using a simple text editor. (GCODE descriptions are from reprap.org). Set the temperatures you want and save the file.

Update: Don't forget to preheat your bed and extruder before running the V2 Calibration, as I'm not convinced yet that the Mk2S actually waits for the correct temperatures before printing the calibration run. Another Update: Did some more testing this morning, Monday 2nd April 2018. the PRUSA Mk2S does wait for the correct temperature before running the V2 Calibration gcode, my appologies to the PRUSA3D team for doubting you.