Hercus 9A lathe 60/63 transposing gear set for metric threading

thingiverse

Cutting Metric Threads on an Imperial Lathe with 8TPI Leadscrew This set of transposing gears is designed specifically for a Hercus 9A imperial lathe, which features an 8 TPI leadscrew and quick-change gearbox. The gear set allows users to cut metric threads on the lathe. As the Hercus is a South Bend clone, it shares parts with other models like the Boxford 9" and Sheraton 9" South bend clones. The 60/63 compound gear provides the necessary imperial-to-metric conversion for cutting metric threads. This gear set offers a small diameter, allowing the transposing gears to fit within the gear train cover. However, it's essential to note that this gear set is not mathematically perfect and may introduce a slight error in thread accuracy. For short threads like those used on fasteners or nuts, this minor error won't significantly impact results. Nevertheless, for long-distance applications like turning lead screws, the accumulated error can become noticeable. In such cases, using the larger 100/127 gear set will provide mathematically correct metric threads. Unfortunately, these gears may not fit inside the gear cover. A quick web search can help you find the tolerance or error if needed. I have also created a 100/127 tooth transposing gear set available on Thingiverse (https://www.thingiverse.com/thing:3352174). When printing the gears, I recommend using PLA as it produces better results than ABS. The included Metric Thread Chart will help determine the correct stud gear and gearbox setting for your desired metric pitch. The gears are 18DP with a 3/8" thickness and feature chamfered edges on the teeth, just like the originals. The following gears are included: * 60/63 compound gear * 42, 36, 33, 30, 27, 24 stud gears The diagram of the gear train is also provided to ensure a clear understanding of how these gears work together. These printed gears run very quietly compared to metal gears. When printing the compound gear, I used 6 top and 6 bottom layers, along with 8 perimeters/walls and 50% infill using cubic subdivision at 50% for maximum rigidity. The spur gears were printed with 6 top and 6 bottom layers, and 5 perimeters/walls to ensure that all gear teeth are solid and the fill extends into a continuous ring within the rim of the gears. This maximizes tooth strength. If you make these gears, please post a "make" so we can see your work. For those who have tipped me a coffee, I offer my heartfelt thanks. Your contributions are very much appreciated. For those who wish to appreciate the many hours of work that went into creating and testing these gears, tips encourage designers to share their work.