This post is just a quick status after assembling and using the Printrbot Simple Metal Kit for about a week. Considering that I had never seen a 3D printer (except on YouTube) before the kit arrived, I think it has been a success. After just over 2 evenings of assembly, I was printing on the 3rd day. Most of the prints have been successful too.
Below is how things look now. Todays additions are two elliptic shaped spool adapters that are now held together on the spool using 2 bolts, plus two rings that keep everything centred. Previously I also printed 2 end-caps that press-fits onto the 32mm PVC pipe. The spool holder now works even better than I had hoped, there is virtually no friction, which is very important for the extruder to produce a constant flow of plastic.
I have seen several other spool holder designs on http://www.thingiverse.com/ , but this one may be among the more compact yet sturdy ones. It can handle spools up to 90mm in width and 110mm radius. There are no stability issues as the sideway movements of the print bed carries relatively little mass. I could possibly clean up the design files and upload to thingiverse, depending on interest. Give a shout in the comments below if you would like to try it.
The extruder tensioner arm extender and the fan shroud have been mentioned before. Both parts were downloaded from thingiverse, and they work very well.
The 4 feet the printer rests on are of my own design. They are supposed to function as elastic springs/dampers smoothing the printer vibrations, and at the same time increase the support area under the printer. Under the feet is a sheet of rubber anti-slip mat. The small contact area of the feet in combination with the rubber sheet creates very high friction, the printer does not move at all during prints.
One thing I learned was that keeping the print bed clean is very important. After a few days, it had started to gather some dust, and the prints began to warp and lose adhesion. As a test I vacuum cleaned everything, then cleaned the bed with some isopropyl alcohol before printing the 2 centring rings on the spool holder. The adhesion was suddenly so good that the blue painters tape would not let go, and followed the parts off the bed! So keep things clean is essential.
Another issue appears to be draughts from windows etc. This tends to cause issues with warping or bed adhesion in general, due to thermal stress. There is probably a good reason why some 3D printers come in closed boxes, keeping constant temperature is one of them. If one does not build a box around the printer, it is anyway an idea to place the printer somewhere where the temperature is reasonably constant, and preferably not too cold.
Speaking of temperature, a heated bed is in the pipeline. I have the parts, but I will use the printer in the current configuration a bit more, that way I can appreciate the upgrade when completed :-)