With the printer happily singing away again I though it a good time to give an update... I had snapped the wire on the heater resistor a while back, and without a spare it ground me to a halt for the best part of a week. There's a lesson there I'm sure! Carry spares if you want to get back on the road quickly. :-)
The resistor was easily replaced, and with the extruder out it was a good opportunity for improvement. I've always been puzzled by others' reported heat up times (time taken to reach target temperatures), and the seeming ease with which similar hot-ends could print consistently at higher speeds. I made three changes to improve my set-up.
Checking the supply voltage I found the reading from my second-hand PC power supply was actually only 11.5v, so I popped the lid, found the pot and adjusted that so it now reads 12v exactly. The second improvement was to wrap the heater block in a little box of Teflon, which I formed from baking tray liner (rated to 260Deg C). I also placed a heat-shield, using the same material, between the cold and hotends. It also neatly keeps the airflow from the fan around the heatsink and away from the hot-end.
(The brass nozzle could do with being a bit longer but that's for another day.)stainless steel downtube to the hot end. There was 'heat creep' rising along this tube and heating the filament too far from the hot-end. This was resulting in the occasional jam. I want that filament to be as cool as possible right until it enters the melt chamber.
Here's the new cooling fan...
The other big change is I've moved from Skeinforge and RepSnapper to SFACT and Pronterface, but I'll save my write-up on that experience for another post. Suffice to say, it's all been positive!
Oh... one more thing... I've also been introduced to this website which is excellent for beginners, like me... http://reprapfordummies.net/.
Keep it printing!