RepRap Prusa i3
Issues to be aware of
Flexibility of frame
The i3's frame is not very rigid, so if the printer is not placed on a solid surface, it will flex unpredictably. This will cause havoc with layer heights and bed adhesion, which require very accurate Z positioning. To do: Make a 440x400mm thick chipboard base to stand the printer on, overcoming the flexibility of the metal cabinet shelves.
First layer not adhering to base
The first thing to check in cases of poor adhesion is the Z axis zero height. The following advice assumes this has been checked and is correct.
Small objects on the first layer are problematic, because the head passing back over newly laid soft plastic within a fraction of a second can peel it back up from the surface, causing a blob of plastic to accumulate on the head.
In this situation, increasing the first layer bed and extruder temperatures didn't help, and neither did adding extra glue to the bed.
The most effective solution I found was to slowing first layer down to 15mms-1. This gives the newly laid plastic time to solidify before being disturbed again by the nozzle.
Found the problem was caused by molten filament entering the gap between the top of the heatbreak and the bottom of the PTFE filament guide, forcing the filament guide up like a piston, and cooling to creating a blockage. I reduced the nozzle temperature to 230deg, and cut a new length of PTFE tubing, trying to get it to just the right length, to avoid any possibility of it being pushed up from the hot end.