Tonight was the first night since the move (and replacing the extruder!) that playing with Skeinforge's settings began again in earnest.
First things first, I wanted to correct this continual negative Z-offset that keeps occurring after a few prints. My current theory is that this is caused by the Z-flag not having a parallel edge causing it to cut the IR beam in minutely different places each time. First task for the evening was to remove the flag and verify if the end was square - it wasn't. A few seconds with a file sorted that out.
Over the course of the evening the negative Z-offset still occurs, but it is definitely not as significant as it was previously. I think tomorrow I'll work on verifying that the X-rods are still level. They may have got knocked out of kilter during the move.
As I mentioned previously I'll be using the Skeinforge settings from mendel-parts.com as the starting point for my tweaking.
I copied the defaults into the '.skeinforge' directory in the users folder. Just using these settings as is doesn't appear to work very well on my Mendel. The feed rate of 50mm/s and flow rate of 1400mm/s does not appear provide sufficient flow, resulting in lots of missing threads on the test pieces and the infill gets very thin in places.
Notching the filament as it travels into the extruder shows that it is moving sporadically during periods when it should be flowing quickly and freely - e.g. around the perimeter of the object. I don't think my sprung pinch-wheel is the problem as it appears to flow freely when I run the extruder from RepSnapper. I think that the flow rate is too high for my melt zone.
I think that the filament is being fed in too quickly for the hot end to melt it fast enough to keep a constant flow. My first tweak is then to slow down the feed rate from 50mm/s through 40mm/s to 30mm/s. This appears to give fairly consistent filament feed now. However, the extruded filament is clearly two thick in places. So I'll need to play with the flow rate and bring that down to get everything back in balance.
A quick test with the flow rate at 1300 (from 1400) gives reasonable results, but I've had better, so more tweaking needed there. Also, it appears to generate GCode that causes RepSnapper to hang once per layer and need to be kicked. Not sure why that one change should cause that, but if it keeps doing it I'll roll up my sleeves and start digging in the GCode.