Huzzah! After two years of muddling about I have managed to coax my Mendel into actually printing something. And it turns out that I didn't even need a new main board!
I had noticed that the electronics would work for about 20 seconds before shutting down so I knew that the problem was not in the stepper controllers but it seemed to me that overheating could be causing a shutdown. Then, when things had cooled down, it could be made to work again. I reasoned that perhaps I had the current set too high on the steppers so I turned them all down and tried it again. Lo and behold everything began working correctly so I proceeded to try printing some small parts.
I managed to get some small things to print correctly, if a little sloppily, so I decided to go for it and try to print a shot glass for the traditional toast to a new machine. The results (.4mm layers, 200C, 50% infill and no heated bed) are below:
In the picture it appears to narrow towards the bottom but that is caused by the camera angle. It actually came out great. There are quite a few blobs but I will experiment with the settings to resolve that. I suppose it is either too hot or the print head was moving too slowly. In any case, it is water tight and shaped like it is supposed to be shaped.
I still don't have my endstops working, which means that I have to set everything up manually. I have been editing the Gcode to remove the homing instructions before and after the print. The most difficult part is setting the position of the Z axis prior to starting. Since I am doing it by eye it is hard to get the height set consistently and I have had to stop several prints because I started them with the print head set too high.I could make a spacer to set the height but I think fixing the endstops is a better use of my time.
I have gone through the few feet of grey PLA that I had and I will be starting into my 5lb lot of green PLA so I went to Lowes and bought an electrical cord reel to wind it on.
Quite a few people are using these now. They are cheap and sturdy. the only problem is that the reel is not split in the middle. that means that I have to wind the whole lot of filament onto it by hand instead of splitting the reel and just dropping the roll in. There are a number of mods for this reel on Thingiverse including a spindle for 5lb spools and some connectors that allow you to modify it so that the reels can be removed and changed. I believe that I also came across an actual printable reel designed for these but I have to go find it again.
I have a few items that I want to get printed now that I have it working. The highest priority, now that summer is coming again, is an adapter to mount a set of relays under the hood of my Jaguar XJS. I installed electric fans last year and the relays that came with them do not fit on the mounting bar of the car. I will have to print those from ABS since it gets pretty hot under there when running the V12 in the summer heat. I think it may get above the melting point for PLA.
I also want to print a set of clips to reinstall a piece of glass in our stereo cabinet. None of the mirror or glass mounting clips available locally will fit this oddball installation. The best thing about this one is that I get to show my wife how useful a Reprap can be!