Sawmills need saws! Millsaws are the large, straight saws used in sash sawmills and other reciprocating sawmills.
Millsaws are typically about six feet long and were about eight inches wide. Over years of use, filing to sharpen the teeth reduced the width. The steel plating used to make millsaws was typically about 1/8 inch thick. Millsaws are intended to make fast, efficient cuts to convert logs into timbers or boards, so the large saw teeth are typically spaced about 1 1/2 inches apart, and are separated by deep gullets to carry away the sawdust.
Millsaws are essentially large handsaws. "the saw having a straight edge or essentially so, like the most generally used hand. saw, or the older saw used in saw-mills. This was the oldest form, the kind used by Noah, if any, in preparing the materials for the ark…"
Overall dimensions of millsaws remained essentially for hundreds of years from the 1400s to the early 1900s.
Millsaws, like other saws, are more than simple metal plates with teeth. The best saws are ground thinner at the back than at the teeth - this allows the saw to move through the kerf without binding.. The saw is tensioned with a hammer to add rigidity along the edge with teeth. As metallurgy and steel fabrication technology improved through the 17th-19th centuries, so did millsaws improve to be reliably straight with teeth tough enough to saw many boards, yet still easy to file when sharpening is needed.
In the first American sawmills during the 17th century in present-day Maine and in Jamestown, saws and other sawmill iron parts along with European millwrights were sent to the new colonies to build sawmills. As sawmills became more common, there likely was the occasional general blacksmith who might try his hand at saw fabrication or repair, but most saws were still imported from Europe.
By the early 19th century, nearly all millsaws were factory-made in large operations both in England and America. See 19th century saw catalogs for examples of mid- and late-19th century saws from large American manufacturers. Even though few sash sawmills continued to operate by the end of the 19th century there still a least a dozen American manufacturers who made millsaws (or at least still had millsaws in their inventories for sale, Machinery and Tools – Woodworking. Seeger and Guernsey's cyclopædia of the manufactures and products of the United States, 1899, section 1854, II Millsaws).
In the 18th and 19th centuries, there were sash sawmills in nearly every New England community that had a suitable site, so there still are a fair number of old millsaws to be found in corners of old barns and antique shops (and of course in sawmill museums).
A millsaw (with the stirrups still attached) was donated to the Ledyard Up-down sawmill a few years ago - it had been found in the woods in a nearby town a few hundred feet from an old sawmill site.
Before and after filing