After I printed out my first 20mm calibration cube, I found my bot was quite accurate for outside dimensions (my 20mm cube measured 19.95mm....close enough). However, I found that holes were consistently undersized. So I created a set of calibration blocks to measure how much undersized the holes are and are they the same for different diameters?
The blocks have a series of holes in 0.1mm increments. The nominal hole is the one circled, then the other holes are smaller or larger in that 0.1mm increment. I found that I had to design a 8.6mm hole in order to get an actual 8mm hole.
The pegs on the other hand, were very accurate. An 8mm peg was 7.95mm....very close to 8mm. So pegs are accurate, but holes are not accurate. Now I wonder if I can tweak this out in Skeinforge or not. The reading I was doing indicated it was not possible to calibrate out easily. But if anyone has any recommendations, please let me know.
Print out the block of your choice then use calipers or dowel pins to test the actual size of the resulting holes/pegs. Then you will know how big to design holes when you need a certain end result size.