To those of you who have been 3D printing for a while, my solution may seem obvious, but I want to briefly explain how I came to the correct settings. Hopefully, by doing this I will both 1) save other people new to 3D printing and RepRap's wasted time and trouble, and 2) remind myself to look out for similar behavior in the future and avoid getting stuck on the same issue.
I had run out of gold PLA, which was the first spool of material that I had ordered and run through my MendelMax 1.5 printer. Here is a link to the gold PLA I ordered: Gold PLA 3mm from Amazon.com
I was very satisfied with this material's performance (I didn't know any better anyway, it was my first spool of material), and free 2-day shipping with Amazon Prime is just too tempting. So for my next spool of material I also ordered from Amazon.com, except I got blue material, and it was from a different supplier: Blue PLA 3mm from Amazon.com
Here is a picture of the material over my machine:
Spool of Blue PLA Over My Machine
I knew I would probably need to adjust the extrusion temperature when I switched materials, so when I started to print with the blue PLA I used a method described on the calibration page of the RepRap.org site. The basic idea is to set the extruder temperature lower and lower and keep trying to extrude material. When you reach a temperature low enough that the extruder cannot push material through the nozzle, increase the temperature by 5 degrees and that's the temperature to use for printing.
This method did now work for me.
I had been printing the gold PLA at around 161 C. I think I did arrive at that temperature using the method described above, and I had good results with this material (barring some times when I had other settings messed up) for several weeks. When I tried the same method with the new spool of blue PLA, I came out with a temperature almost 10 degrees lower. As mentioned in previous posts, though, at this temperature the material was not sticking to the build plate.
I tried increasing the temperature of the extruder and build plate, sometimes together, sometimes separately, and I tried a range of temperatures for each from as low to as high as I thought might be reasonable. I think I tried a build plate temperature from 50 C up to 80 C, and a material temp as low as 150 C and as high as 175 C. I also kept cleaning the glass over and over, wondering if that had something to do with the failures.
At one point I thought I had it, and a print got through the first layer of a large plate of parts for the lathe I'm printing, but when I came back down after the print had gone through maybe 10% of the second layer, I found that some of the pieces had lifted off and stuck to the hot end, and this is what I pulled out of the machine:
Melted Glob From Parts Not Adhering to Build Plate
That was about a week ago, after over a full week of trying with no success. Finally, this past Tuesday on a whim I decided to jack the temperatures way up, to 181 C on the extruder and 73 C on the HBP. I was shocked to see how well it worked--I felt like I had come back off the DL just in time for the playoffs.
The 181 C came from posts I had read online about printing PLA around these temperatures. It seemed like I was printing the gold PLA at a relatively low temperature compared to other people, so I really thought my machine just wasn't reading the temperature correctly. I guessed the 161 C I had been using for gold was probably more like 175 C in reality, so going much higher than that would be a bad idea. Also, I had used the method described above to find the optimum temperature, and that lead me to believe that the blue PLA should be printed at a temperature something like 30 degrees cooler than the 181 C that eventually worked.
The 73 C temperature on the HBP wasn't such a stretch, since I had noticed that up until this temperature range it did seem to help with the issues I had been having. It just couldn't solve them completely without me also adjusting the extruder temperature.
Right now I'm printing Plate 2 from the Lathe prints, and it
Printing Lathe Parts with Blue PLA
Seeing it run at 181 C, it's hard to imagine why I did not know to go to this high of a temperature before. I was going on what I thought was a proven way of calculating optimal extrusion temperature, and it ended up causing me to not try high enough temperatures.
I also have been cleaning the glass with 91% Isopropyl Alcohol (rubbing alcohol). This seems to be working well, although I have no real way to separate its effect from the other variables that I have been working with.
So, in summary, if you are having trouble with adhesion of the first layer, you should try higher temperature to see if that allows the material to bond more strongly with the surface of the glass you're printing on. In the end, there are lots of variables that come into play, but at least you will give yourself a chance to reach a temp that works, even if it seems far outside of the range suggested by using the min possible extrusion temperature + 5 degrees.
D
PS - Sorry for the title, just couldn't help myself . . .
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