Multiple bearing stack retention

A method for arranging concentric, independently rotating shafts for a rotating gear train system, the method comprising:

• providing an inner shaft;
• operatively coupling the inner shaft to a rotating element;
• arranging an outer shaft radially outward from the inner shaft, the outer shaft concentric with the inner shaft;
• arranging a first bearing stack radially outward from the inner shaft, the first bearing stack comprising at least one preloaded ball bearing;
• arranging a second bearing stack radially outward from the outer shaft, the second bearing stack comprising at least one ball bearing;
• and
• mating a bearing stack retainer with the first and second bearing stacks to hold the first and second bearing stacks in position with respect to the inner and outer shafts, the bearing stack retainer coupled with the outer shaft and rotating with the outer shaft.

A gas turbine engine comprising:

• a fan section, the fan section including a rotating element;
• a compressor section downstream of the fan section;
• a combustor section downstream of the compressor section;
• a turbine section downstream of the combustor section;
• an inner shaft, the inner shaft operatively coupled to the rotating element of the fan section;
• an outer shaft, the outer shaft concentric with the inner shaft and arranged radially outward from the inner shaft;
• a first bearing stack, the first bearing stack arranged radially outward from the inner shaft and comprising at least one preloaded ball bearing;
• a second bearing stack, the second bearing stack arranged radially outward from the outer shaft and comprising at least one ball bearing;
• and
• a bearing stack retainer, the bearing stack retainer mating with the first and second bearing stacks to hold the first and second bearing stacks in position with respect to the inner and outer shafts.