Layer not sticking is most of the time a bed leveling issue.
Bed Leveling is not only the part to get it about the thickness of a paper from the nozzle, but also adjusting afterwards to ensure optimal layer adhesion. For a 0.2mm layer, you need to get the bed that distance in the position the nozzle will be when it prints the first layer (while the printer is printing the first layer – which is why we use extra lines of the Skirt/Outline option). This is the difficult part (some slicers use your leveling as the first layer gap, others add the set first layer height on top of your leveling gap [for these you need to account for it]).
Half of the first layer height, is how far off you can be from the ideal gap as an absolute max (for 0.2mm layer height, that is between 0.1 and 0.3mm). The Di3 uses M3 screws with a pitch of 0.5mm for bed adjustment – 0.1mm difference is only 1/5th of a turn.
The Di3 have one very big weakness: The X axis does not stay level. Since it have 2 motors, they can move independently while powered off (or disabled). Leaving the printer off or steppers disabled for more than a few hours is enough to have it shift slightly. I use http://www.thingiverse.com/
Bad filament can cause similar issues, but usually you can level a bit closer and it will still stick.
A glass plate is a very good idea and recommended – Adding a glass bed
Yes, your printer have the holes for the end-stop adjustment and thus adding the glass should be easy.
Placing the glass on top of the buildtak, not ideal (especially if you want to use the heatbed for PETG or ABS) – the buildtak on the printer have a paper based glue, which is very insulating. Real BuildTak is a vinyl type of product which conducts heat easier.
The easiest way to remove the buildtak on your bed:
- Heat it to about 50C (no need to heat the nozzle too), but leave it for a few minutes at 50C (so that the heat can get everywhere).
- Now carefully and slowly start peeling in one corner.
- If glue remains in a spot, you are going too fast (this takes patience, on my second try it took about an hour or more).
- After you have the whole sheet off, there might be residue spots left, using the glue side of the sheet, stick it on top of the residue spot (rub it a bit) and peel that part again (don’t stick the whole sheet, only a small part) – this should lift the residue off in no time.
Peeling it off cold will result in a mess (this is what happened on my first try – took 3 days to clean, and it left scratches from the cleaning).