Yesterday's printing was a tale of two worlds - the first 4 prints were nearly perfect with only one print having an extremely minor flaw on the first layer. So all problems solved! Not so fast, the next print was as frustrating as it can get.
The headband we are printing - the RC2 model from Prusa - has a very narrow footprint and on the first layer, things can go sideways as the hot end traces a path almost back onto itself. If the extruded material does not stick, the PLA hardens into a stringy mess. This occurred 2 times in a row, so on the 3rd occurrence, I removed the mess, and applied some diluted glue stick glue before the second layer. This worked and the remaining part of the print executed without issue.
So what the h*ll is going on. On the next and last print of the day, I decided to investigate what was going on. So typically if something is not sticking to the hot plate, then the hot plate is not hot. So I took a temperature gun and pointed it at the hot glass plate in the region where it was not sticking -- it should be 60c but to my amazement, it was 49c ???. I took a look at the glass plate where it rests on the aluminum hot plate. There was a gap where I could insert a piece of paper. Bingo - that was this issue - but why. I looked at the clips hold the glass plate to the aluminum hot plate and discovered the rear left clip was almost in the center of the plate, not to the outer left side. Ugh! When I had replaced the glass plate after washing, I did not pay attention to the location of the rear clips. I typically reach through the vertical post of the printer to add the clip and being left-handed, there is a tendency to favor the right side thus locating the clip near the center.
So once I understood this -- how to fix it. Just place the clip closer to the left side and ensure it is aligned with the front clip. Almost but not quite!
This morning's first print again lifted, even though I had ensured the clips were aligned to the left side, but clear of the hot end. Hmmm. I checked the temperatures and was still seeing a little drop in the temperature on the left side. I added a fifth clip along the left side about 2/3 of the way from the front to clear the print and hot end. I checked the temperatures again and this solved the problem.
On to the second print of the day -- I rotated the plate after washing and now the lifting issue as on the right side -- What the H*LL! So I stopped the print and clean the surface once more. I rotated the plate once more so the logo was facing the right (power supply) and printed the RC2 Version 3 that moved he print forward on the print area. This took and seem to be printing fine.
Bottom line - I believe he glass plate is warped and depending on the rotation of the plate, the "cold spot" moves. So I need to determine the exact location and apply an extra clip if need. I have also created version 4 of the g-code that has a high bed temperature of 65c and a hotter extruder temperature of 210c. Also, version 4 is located toward the rear of the plate. I will use version 4 on the next print.