David G. in Mexico City asks: How can I control or prevent movement of the neck? If I change string gauges will this affect the neck?
Roger Sadowsky answers: The main factor that affects neck movement is humidity. Generally, increased humidity causes necks to back-bow and low humidity causes necks to front bow. These movements can all be corrected with truss rod adjustments. The amount a particular neck moves in reaction to humidity changes can vary depending on the personality of the particular piece of wood. One particular neck may stay stable and never require an adjustment and another neck may require seasonal or more frequent adjustments. We purchase our neck wood at least one year before we use it to maximize the stability of our necks.

Most bass necks will require a small truss rod adjustment when switching string gauges.