Monday, December 14, 2009
Getting overhangs right
When I bought my Rapman 3 I ordered two extruders and an extra extruder barrel drilled to 0.3 mm. When I assembled the extruder, I thought I had picked up one of the two 0.5 mm extruders. Instead, I had got the 0.3 mm one.
Oddly, I hadn't noticed the difference. The Rapman 3 extruder's filament pump was more than powerful enough to force 0.5 mm flow rates through my 0.3 mm extruder orifice without complaint. Thus, I was able to print what appeared to be 0.5 mm objects ... until we got to overhangs. When the extruder got to the overhangs it literally squirted the hot plastic into the voids festooning the print with what looked like plastic tassels.
I'd have probably never figured it out what was wrong save that my extruder orifice jammed. When I cleared it with a 0.25 mm strand off of a multistrand wire, I noticed for the first time that the ABS being extruded looked a bit thin. In fact, when I measured it, what was coming out was 0.38 mm in diameter. There was no way a hot filament that thin was coming out of a 0.5 mm orifice. That was when I realised that I had put in the 0.3 mm extruder barrel in error.
Knowing that, I reduced the flow rates and layer height to 150 and 0.25 mm and the overhang problem magically went away.
The new print is, of course on the right.