I was experiencing similar issues on my Raise3D Pro2Plus. I've printed near 20 small cylinders to try and find tune the settings to get densities that are close to the theoretical density and right now am sitting comfortably around 80%. Here is what I've found
- Temperature of the build plate and extruder have had a large effect on the quality of the print (obviously), to the point where 3-4° have a noticeable effect on print quality. I have settled on an extruder temperature of 252°C and a bed temperature of 82°C. I also print in an enclosure which I imagine is necessary due to the shrinkage seen in PMMA.
- A lot of my problems were with bed adhesion. The Buildtak that came on the Raise3D worked for a while but the higher temperatures eventually caused the adhesive to fail and bubble up where I was trying to print. Blue tape and purple glue stick worked sometimes but would often detach halfway through the raft. What I've found that works reliably is Kapton tape covered in purple glue stick. This has yet to fail me and the only downside is that I often have to reapply the Kapton after every 2 or so prints which is a small price to pay for me as my regular prints take 3-4 days.
Just for reference I print at 30 mm/s, 1mm nozzle, 0.29mm layer height. I definitely get your frustration on trying to find a good resource for settings. Most I could find was generic ranges for temperatures and speeds.