prints won't stick to print bed

I've had great success with my RepRap Prusa i3, but suddenly nothing sticks to the print bed. I'm using a heated glass bed, cleaning with alcohol between prints, and all was well until I tried to use ABS. That didn't work well, so I switched back to PLA. Suddenly the layers weren't thick enough, the extruder stopped extruding properly, and the nozzle started "blobbing". Soon after this the nozzle clogged. I cleaned the nozzle, but still nothing sticks and the nozzle blobs. The brim sticks until the nozzle comes back for the second pass. Then the nozzle just drags everything around the bed until I kill the print. I'm using Repetier Host for slicing and printing. Nozzle temp is 215-220 and bed temp 60-70 (I've tried many combinations, but nothing seems to make a difference.) I appreciate any ideas or suggestions to fix this.

Just about everyone has their magic formula for bed adhesion.

I hardly ever use PLA anymore, I think that I still have a spool in a sealed bag, but I haven't used it since May. Blue tape seems to be a pretty good solution for PLA, even unheated.

It does sound like you're having other issues though. Clogging will cause you no end of grief. It kind of sounds to me like you may have had some issues with the ABS. ABS demands higher temperatures, so if you increased nozzle temperatures in order to print it, your actual temperature may be even higher. this can cause problems with stuff like PTFE or PEEK in the hot end throat, which is a common cause for clogging. A cold pull from your hotend will give you some idea of the condition of these parts. If that is a problem, nothing else that you do is going to solve the underextrusion problem.

Once you have the clogging problem resolved, you'll probably find that it's fine the way it was before. As I said, just about everyone has their own solution for bed adhesion. I am looking into new stuff for ABS, but haven't used the MBot printer for a couple months (Which is what I print ABS on.) I've been almost exclusively using the leadscrew printer, which has so far only been used for PETG. I do have a couple things that I want to use ABS for, so I'll be firing it up again soon. No plans to be using PLA for anything any time soon though. Maybe when it's time to do some Christmas wrapping I'll pull out some brightly coloured PLA again.

---

MBot3D Printer
MakerBot clone Kit from Amazon
Added heated bed.

Leadscrew self-built printer (in progress)
Duet Wifi, Precision Piezo parts

One thing you might want to try if your PLA is not extruding properly. Extrude 300mm or more at 10C higher than you were trying to print the ABS. Then run another 200mm or so at your normal PLA temperature. I’ve found this helps when switching material it helps purge out old material. I generally do this when I go between PETG, Tglase, Ninjaflex and PLA+. I usually extrude the new material at 10C higher than the previous material if the previous material used a higher temp.

With this practice, I’ve not had to disassemble to clean or run any sort of cleaning filament. A company I once worked at that did a lot of industrial plastic extrusion did something similar to reduce changeover times and I adapted it my setup. Just a suggestion.

Thank you for help. The cold pull worked perfectly. All is well now, and I'm going to explore a departure from the PLA and move on to ABS and others. Thanks again,
Rick

Thanks for the suggestion. Now that I have the hotend cleaned out and all is working as it should, I'll follow your advice and run a couple hundred millimeters through when I need to change. Thanks again,
Rick