I'm printing some objects on large plastic tiles in order to obtain a permanent adhesion between the printed parts and the substrates, so my problem lie in the impossibility to use a skirt to prime the nozzle, because the substrate is part of the finished product.
So I'm here to listen to your suggestions about effective priming procedures, whether they are just ideas or not.
Now I operate purging the nozzle at the bed side, cleaning the nozzle on a brush and settings the correct amount of retraction in order to let the extruder reaching the print start position without blobs or excessive material gap inside the nozzle.
This kind of procedure is prone to inconsistent results due to the high number of variables involved (ex. the distance between the brushes and the print area) leading to a no-extrusion, or over extrusion with blobs, in the first print path.
I also "hacked" S3D in order to produce a skirt at a very high Z position (ex. 0,7 mm) to produce a skirt that just lightly touch the substrate, but the obtained lack of adhesion for the skirt produce strings inside the print area and the accumulation of the material on the nozzle.