Dragon print.

Just some pictures of the first successful print with the new fan configuration.
I printed this dragon from loubie on Thingiverse. Since the figure was printed at 50% scale (total height is about 8 cm), the front legs were a bit too fragile, so I added a little base to make the model a bit stronger.

Printed with 0.15 mm layer height, printing time about 3 hours.

Object cooling

The previous fan was used only to make sure the top of the hot end did not get too hot. I designed a guide to get the cooling air to flow both through the vents in the hot end and at the same time on the printed object around the hot end. The air guide  looks like this:

Installed, side view:

Installed, front view:

New hot end for Delta printer.

I wrote about the problems with the hot end before. Though I did get the hot end to work, it only worked at slow speeds (25 mm/s) and the extruder motor was visibly loaded more that what should be necessary. The extruder's hobbed bolt also slipped regularly leaving holes or weak parts in the printed objects.
The friction of getting the filament through the hot end (0.5 mm nozzle) was just too high. I decided to try another hot end, the J-Head, and this has been working fine for 2 weeks now. I bought the hot end here: http://reprap.me/ 
As the top part of the J-Head is bolted directly to a part made of PLA, I wanted to make sure the cooling was taken care of properly: a separate fan is blowing air through the holes of the J-Head to make sure the top part will not melt the PLA.

To cool down the printed PLA quickly I currently use another, stationary, fan. This caused a problem with reliable flow of plastic because the heater block was now being cooled too much. Too much cooling was prevented by insulating the heater block (not visible in the picture about yet) with some ceramic tape. I will make another solution for the PLA cooling later, but for now the quality (and speed) of the prints is greatly improved.

The Stanford Bunny from thingiverse:

0.15 mm layers, object about 6 cm high.

Moiré pattern, part 2

The problem with the moiré pattern which was visible in the prints last time has been fixed. I got several suggestions about possible causes. The one I focused on first was the possibly that the pulleys of the wires which are moving the "axes" up and down where not round. I got better quality pulleys, but this did not solve the problem. While trying to debug the issue I noticed that when the printer was running really slow, the sound of the printer was changing. I vaguely remembered a blog post about problems with the stepper motor drivers somewhere and I found the problem. It turns out the current which is running through the motor is too small  to actually get the motor to move in certain phases of a rotation. The solution was quite simple: increase the current through the motor. The current through the motor is adjustable with a tiny potentiometer on the stepper driver board. The previous setting was so that the stepper motor would have just enough current to not loose any steps (full steps).  I now increased the current so that it is enough to drive the motor in all phases (all 16 microsteps) of a full step. The blog post I found the information in is here:  hydraraptor Stepstruck.

The print quality increased a lot: