Filament not sticking.  

RE:

IPA doesn't really clean the plate, it just moves oils around. Try dish detergent like Dawn and warm water. 

1. Yes, for a 0.4mm nozzle it should be 0.45mm thick. This is set in the slicer under "Default extrusion width"
2. Same width extrusion width as in #1
3. Correct, the Core One uses the load cell and creates a mesh of the plate surface. Probably the nozzle is not getting close enough because filament was stuck to the tip of the nozzle when it was probing the bed. Try cleaning with a brass wire brush. 

RE: Filament not sticking.

Hey,

Please check that the nozzle sits tight in the holder and the thumb screws are tightened correctly to avoid that error. Put the bed to the lowest position and check the screw tightness of the z-axis nuts. Maybe loosen and tighten them a little bit for optimal play. It is hard to say but the whole arrangement is usually unter tention, because of assemble first and put in linear rails later. Maybe removing that tention will lead to more consistent results.

RE: Filament not sticking.

I see a lot of red accumulation on the nozzle tip so I'd agree with @hyiger in point 3. Clean your nozzle to avoid buildup from interfering with the mesh-bed leveling. Heat the nozzle to 170°C or so and gently scrub the buildup off with a brass brush. (The soft brass brushes sold for gun maintenance work well for this.)

I'm another proponent of occasionally cleaning the print beds with Dawn, but I use water as hot as I can stand and scrub with a plastic bristle brush. For the powder coated sheets (satin and textured) I also put the freshly cleaned sheet back on the bed and crank it up to 100°C (or higher) until the printer automatically shuts the bed heater off to drive off any moisture that accumulated between the powder coat grains to avoid rusting sheets. If I remember I flip the sheet once after a few minutes at temperature.

For daily maintenance cleaning (between print jobs) I use 90%IPA, mostly out of habit. I haven't tried it yet, but Grant from 3D Musketeers swears by using an ammonia based glass cleaner (like Windex) instead of IPA for daily maintenance cleaning. He claims that will actually pick up finger oils instead of just smearing them around like IPA does.

RE: Filament not sticking.

I switched to BIQU Cryogrip plates and don't clean them at all except an occasional wipe with a dry cloth to remove debris. 

RE: Filament not sticking.

I finally found the problem. FYI this is a Core One converted from a MK4S. I tried the dawn clean and it did no good. Some suggested nozzle cleaning, it did no good. I've used the PEI plate and same nozzle for 2 years with no problem and always cleaned with a clean paper towel and 99% IPA. I bought a brand new complete hot end with 0.4mm nozzle and got the same bad results.

I used all the defaults on Slicer 2.9.4 that I downloaded at the time the conversion was complete.

I decided to make a few changes. I changed the 1st layer height from 0.2 to 0.3, Changed the 1st layer bed temp to 65 C from the 60C I've always used, changed the Z retract from 0.7  to 2, and a few  other temps. All the changes are shown in the attached PDF file.

I just completed my 5th part with these new settings on the same red filament as well as galaxy black with ZERO problems.

I don't know what the old slicer defaults were, but that's what I used for 2 years. I calibrated Z and the touch sensor on the original and new nozzle. I don't know which setting helped the most but I suspect the 1st layer thickness is what helped the most. All I know for sure is the settings in the PDF file I attached have made the MK4S to Core One conversion work perfectly.

PRUSA_PLA-SUCESSFUL_SETTINGS_2.9.4

Posted by: @tunasalmon-2

I opened a new Prusa filament (Lipstick Red). Printed fine Sunday. Monday it was not sticking to the plate in some spots. I put it in a dryer at 50 Deg C for 5 hr. Same me problem . The plate is cleaned each time with 99% IPA and is spotless. Printing at 215 (That's what the spool says) with a 60 degree bed temp. Wednesday It made the mess shown in the picture. 1. The little test strip in the front was 0.45mm thick. Is that right? 2. What should the purge string diameter be? 3. They say do not use a Z offset because the Core one measures where the plate.  It appears the nozzle is not getting close enough to the plate