In an application filed with the U.S. Patent office on June 22, 1891, Joseph Gearhart submitted his invention for a Mold for Casting Knitting-Machine Cylinders. This application would become Patent 468,171.
As the patent says, The object of my invention is to construct an apparatus for casting knitting-machine cylinders, having grooves running longitudinally in its outer surface for the needles to move in and a crown or cog wheel at its base by means of which the cylinder is rotated, which construction is shown in my patent, No. 457,643, dated August 11, 1891.
The modern die-casting process was not invented by Herman Doehler until 1906, so the introduction of this process to the American factory was still 15 years in the future. Therefore, Joseph’s choice was to invent his own mold. He did, however, later seek out Herman Doehler and ended up awarding the Doehler Die Casting Company of Toledo one of its first contracts, for the manfacture of the Gearhart Knitting Machine cylinder. To me, this is an amazing piece of history, for it not only demonstrates Joseph’s inventiveness, but it also ties him directly to the major technological achivements coming out of the big manufacturing cities of the early 20th century. I plan to expand on Herman Doehler and his relationship to the Gearhart Knitting Machine company, and this will be the subject of a future article for the archives.
But in 1891, Joseph was casting his own cylinders from his own small factory in Clearfield and having fairly good success with the effort. His first mold was for a 3.75″ diameter cylinder, which was larger than the 3.25″ diameter of the original wooden cylinder.
He used a combination of zinc and lead for his cylinders. Due to the low melting point of this pot metal, sophisticated foundry equipment and high-pressure steel dies were not necessary. Therefore, his hand-operated mold was sufficient. However, pot metal could be prone to instability over time, as it had a tendency to bend, crack, and pit with age. The low boiling point of zinc and its fast cooling often allowed air bubbles to remain in the cast. Also, unless the mold was pressed under very high pressure, as was Herman Doehler’s die-castings, then the casting could have runs. Joseph’s first cylinders showed both runs and pits, but he eventually eliminated both entirely. I believe the 3.75″ cylinder in the archives might be the very first metal cylinder. This is significant in that it shows several large runs and was no doubt Joseph’s moment of discovery that he needed more pressure in the mold.
His next cylinder was a large one, measuring 5 inches in diameter. I am not sure why he constructed a cylinder this large, but I may discover the reason with some more investigation. In fact, if anyone has information which would explain the size chosen for all these cylinders, I would very much like to hear from you. From this point forward there were very few, if any, runs or pits.
Joseph constructed three molds, for 3.75", 5", and 4.625" diameter cylinders. The 4.625" diameter cylinder was the final size, and became the standard size for all subsequent cylinders. The mold itself is shown in the patent illustrations.
It took six pages to describe the construction and operation of the mold, so this invention is not as simple as one might think. In fact, as I read over the text, I am left wondering how long it took him to figure all this out. Its good to know that he did finally figure it out, because all the Gearhart Knitting Machines manufactured from 1891 through 1915 [fact-check with Doehler] had their cylinders constructed from this mold.