Many of the tools and devices described and illustrated in this volume we designed and used ourselves; others were designed under our personal supervision; while others have been selected from published articles written for the technical press under our own name and various pen names. For many other descriptions and illustrations we are indebted to the kind courtesy of the editors of American Machinist, and Machinery, respectively, and here ex tend our thanks and sense of deep obligation to these journals for the privilege of using extracts and illustrations of articles which have appeared in their columns. For a large number of practical kinks and points we acknowledge our indebtedness to the numerous concerns with which we have been connected, and to the fellow workers with whom we have associated.