A composite housing and a method of assembling a composite housing for a scanning assembly. A body of the housing defines an opening of a first perimeter. A polymethylpentene scanning plate is provided which has lip with a marginally larger perimeter than the first perimeter. During assembly of the composite housing, at least a part of scanning plate is thermally contracted to allow it to be positioned within the opening such that the peripheral side surface of the scanning surface faces the edge of the body. When the scanning plate returns to ambient temperature and expands at least a portion of the side surface of the scanning plate engages the edge of the body.