Moiré pattern

There are some artifacts showing up in the prints of the delta printer. Depending on the shape of the object they are more or less visible. I printed a flat vertical object, 80 x 80 mm, to be able to see the effect properly:

Most of the time this is no problem, but there may be some ways to tune the printer to minimize the deviations.

Interesting discussion going on on the google forums here.

Hot-end clogged

In the new delta printer I use this hot-end from RepRapWorld. I have used exactly the same hot-end in the previous printer and it has worked very well there. The hot-end should be made according to these specifications.
When pushing the filament through by hand before mounting the bowden cable, I noticed there was a lot of friction. When printing the first objects the extruder motor started to skip steps, or the hobbed bolt would slip the filament back before the filament got stuck completely and no more plastic was coming out.
When removing the plastic from the extruder, the plug looked like this:

There are 2 things wrong here: there is a bit of a flat end which is larger than the 0.5 mm hole where the molten plastic leaves the hot-end, and the angle of the top of the plug seems to be too big.  The specifications state a 90 degree angle drill bit should be used for the inside and there should not be a flat area at the end. This is part of the original specifications:

I don't have a proper 90 degree 3.5 mm drill bit and my local shop did not have one either. So I modified a normal 120 degree drill bit and drilled the hole a fraction of a mm deeper. After this, the plastic is flowing better. I would still like to have it flow faster, but at least now I manage to keep the printer running for more than an hour. The maximum speed is about 40 mm/second, I think on the other printer I manage to get more, but I don't have a reference figure at the moment.

Delta printer progress 2

Since last time, I added carbon fiber reinforced rods between the ball joints on the carriages and the ball joints on the extruder platform. 

I also added some switches to each X, Y and Z "corner" which will be used to home the extruder. The standard homing procedure which is used, is to quickly move each carriage over the axis up until the switch is closed. It then moves down a few millimeters and moves up slowly until the switch is closed again.

The switch at the top:

You can see the homing procedure, the switch and the carbon fiber rods in this video:

In this printer the extruder is split into two parts: the extruder motor which is mounted on the top of the machine and the extruder hot-end which is mounted on the extruder carriage. Between the motor and the hot-end, the filament travels through a teflon tube, just like a bowden cable.

The motor part is here:

The parts are borrowed from RichRap's 3DR printer which in turn is based on the Greg's Wade extruder.

The first half of the hot-end is mounted on the carriage here:

The first print of the printer failed, more on that later. But the printer is working as can be seen in this video: