Maybe how you are putting the paint down. Whether spraying metal or brushing wood, keep working along the wet edge. In other words, only overlap the last portion of paint that was applied. Have the paint flow out of the brush tip onto the unpainted portion next to the last painted section. Keep flowing it out as you move the brush along, either adjacent or away from the previous section. Then bring the brush back over the freshly laid paint overlapping it onto the edge portion of the previous section in the direction of the grain of the wood. Traditional oils and long oil primers can be worked in both crosswise and with the grain, but final tipping off is always with the grain.