Danny Dunn and the Smallifying Machine

Danny Dunn and the Smallifying Machine is the eleventh novel in the "Danny Dunn" series of juvenile science fiction/adventure books written by Raymond Abrashkin and Jay Williams. The book was first published in 1969.
Summary.
Professor Bullfinch has created a machine for the government which will shrink objects and be used for spying. When Danny sneaks into the lab, he and his friends discover the machine and try to use it for a problem they have been dealing with at school.
Editions.
McGraw-Hill
MacDonald and Jane's
Archway Books
Pocket Books