I am trying to assemble the rear wheel of my bike. I have sorted the spokes into two groups by their length. It seems like I do everything correct according to video tutorials and articles but when I put the last group of 8 spokes they appear to be longer than needed and the nipples come out of the rim by 0.5-1.0 cm. What is the reason ? Is it a common problem ?
Assuming that spokes are installed correctly, it might simply be that the axle is not centered. i.e. you under tightened the spokes on the side of the rim you built causing spokes to poke out the rim on the other side. it is important to evenly distribute mounted spokes around the rim when building a rim.