Waltham - Mrs. Helen (McGuire) Preston, of Waltham, died Saturday, November 3, 2007 in Maristhill Nursing Home, Waltham. She was 87. A lifelong Waltham resident, Mrs. Preston had worked as a secretary for Waltham Tool and Engineering until her retirement in 1953. She was a member of Saint Charles Borromeo Church in Waltham. Mrs. Preston was the daughter of the late Michael and Mary (ODea) McGuire and the sister of the late John McGuire, Louise Cassie, James McGuire, Mary Scalia, and Francis McGuire. She is survived by her husband, David Preston; her children, David Preston, Jr. and his wife, Barbara, of Woburn and Debra Masterson of Waltham; seven grandchildren, two great grandchildren, and many nieces and nephews. The Funeral will be held Friday at 9 a.m. from The Joyce Funeral Home, 245 Main Street (Rte. 20), Waltham followed by a Funeral Mass in Saint Charles Borromeo Church, 51 Hall Street, Waltham, at 10 a.m. Burial will be in Calvary Cemetery, Waltham. Visiting hours will be held Thursday from 2 to 4 and 7 to 9 p.m.