Getting it right

Having put the Prusa kit together and calibrated it, I printed a small logo and it seemed OK. On looking closer it didn't look quite as neat as I expected. I decided I needed to check a bigger print. First I changed the spool of filament to orange and recalibrated. 

I think I'll describe the process of designing an object in another post, so I'll just say that I created a very simple square drink coaster. It is 100mm x 100mm x 3.5mm. When I tried to print it the print failed. 

 

The photo is not very good, but you can see that there are diagonal gaps and clearly the corner has come unstuck and curled up. The print head snagged on this raised corner and the whole object came unstuck. I watched this all happen and it was clear that the extruded filament was not properly adhering to the print bed. A couple of stray lines wafted about and where this overlaid the print this made a raised bump. As the nozzle passed this it snagged and started to move the object. 

It seems that there are two main reasons for failing to stick: the print bed might need cleaning or the print nozzle is not aligned on the bed. I cleaned the bed before the print, so that left the calibration issue. I re-read the instructions and some comments online. It seems that the the nozzle needs to be very close to the bed, but not touching. As the line of plastic is extruded it needs to be slightly squashed by the moving head. I had set the head higher than that. The First Line Calibration allows a fine control of the height of the nozzle to be made using the knob on the controller. I wound the head down by another 100 microns. I ran the print of the coaster again and this time it printer well and looked much neater. 

Keeping the print bed clean seems to be important, though the manual does say that it doesn't need to be cleaned before every print. I'm trying not to touch the centre area where the prints are made so I don't leave finger marks. The kit came with two cleaning wipes soaked in isopropanol. I need some more. I have some lint-free cloths so I thought I'd buy some liquid isopropanol. The only suggestion as to where to buy any is pharmacies. It seems that the national chains of Boots have decided not to stock it, not sure why. When I looked around the local villages almost all of the pharmacies have been sold to Boots, so no joy there. Eventually I did find an independent pharmacy that had a few wipes which will do for now. I ordered a bottle of the solvent online which should arrive shortly.