RRP Mendel - occasional hang in middle of build

I finally seem to have successfully calibrated the Mendel. My prints are not too bad save the occasional blob around the edges. However, one thing that has been a bit frustrating is about 30% of the time my builds hang somewhere in the middle of the process. A couple of times they hung when I touch the hot end with an exacto kinfe to try and dislodge a blob that was baking onto the side of it. This was while it was moving. It was like I coupled some sort of noise (static?) into the system through the hot end block maybe via the heater resistor? I also notice that my extruder occasionally does not turn on but when I touch a small screwdriver to the trim pot it kicks into action. Weird stuff. I am guessing static, though I am usually pretty good about grounding myself before touching anything that could be sensitive.

Anyone else have a melzi based reprap that hangs?

Thanks in advance,

Ben

Is this from a USB print or from the SD card? Generally RepRaps are much more reliable printing from SD

Printing via USB and PC has been just as you describe above. Hangs for no apparent reason.
Printing form SD card has worked great. I have only had 2 issues with a print stopping from SD card. First was a wire on my extruder stepper breaking and the other was when I ejected the card while printing.

Interesting. I'll try printing from the SD card. Do I right to the SD card over the USB link or do I need an SD card writer separate from the printer?

When my extruder hangs, it is only the extruder that is hung. The other axes all carry along just fine, oblivious to the lack of resin coming out the tip! Today I found that the extruder did not start up with the rest of the motors, but when I touched one of the mounting screws of the PCB (which I think might be shorted to ground on the PC and simultaneously touched the potentiometer for the extruder, it jumped to life and then proceeded to run fine. Strange indeed!

If you're using pronterface, you choose the SD card button, it prompts for a file name, and then it basically prints the file to the SD card. Once on the card, you can start a print either from pronterface, by choosing ta correct file, or, f you have one, through the LCD control panel.