I haven’t posted much about the 3D printer recently (or indeed about anything else). This is partly because I have been trying to work out what was the cause of poor print quality. I’ve finally worked out what the cause of the problem was. I’d been finding it increasingly difficult to print larger objects, particularly those which involved long continuous print movements. The symptom seemed to be a lack of material being extruded. I’d tried turning up the filament feed rate, but this only led to the extruder slipping as it tried to drive more filament through the print head. I turned up the temperature setting, to make it easier to extrude, and this worked over shorter movements, or at lower speeds. I could only get half-decent results by printing very slowly, with a feed rate of 120%.
The cause of the problem turned out to be very simple. The resistor used to heat the hot end simply could not provide enough heat to melt filament at the required rate. At low speeds, no problem. At higher speeds, insufficient power meant taht the hot end simply could not maintain the required temperature. Short distances were OK, because the hot end had time to heat up between extrudes.
The solution was to replace the resistor in the hot end with a cartridge heater. The J-head kit I bought came supplied with both options, and for some reason I can’t remember, I originally went for the resistor (there’s a picture in this previous post). Ten minutes of disassembly, rewiring and reassembly is all it took to fit the new heater. The hot end now reaches operating temperature much more quickly, and stays there very accurately, even if I turn the feed rate up and use a cooling fan. Goodness knows why I didn’t try it before.