Hercus 9A lathe 60/63 transposing gear set for metric threading
Description
For cutting metric threads on an Imperial lathe with 8TPI leadscrew. This set of transposing gears is designed for a Hercus 9A imperial (inch/english) lathe (9" model A lathe with quick change gearbox and 8 TPI leadscrew) and is used to cut metric threads. The Hercus is a South Bend clone, and shares the same parts, as does the Boxford 9" and Sheraton 9" South bend clones. This gear set uses the 60/63 compound gear to provide the imperial to metric conversion. The 60/63 compound gear provides for a small gear diameter and allows the transposing gears to fit within the gear train cover. The 60/63 teeth gear set is a very close approximation, however is not mathematically perfect and there is a very small error. For cutting short threads such as those for fasteners, nuts etc this is fine however the slight mathematical "error" accumulates over long distances such as turning a lead screw; in which case using the larger 100/127 gear set will provide a mathmatically correct metric thread (albeit the gears probably will not fit inside the gear cover). A quick web search will enable you to find the tolerance/error if required. I have also created a 100/127 tooth transposing gear set. https://www.thingiverse.com/thing:3352174 I printed some of the gears in PLA and some in ABS. Both work OK, however I prefer the PLA versions. I have included a recreation of the Metric Thread Chart for determining the correct stud gear to use, and gearbox setting to select to turn the desired metric pitch. Gears are 18DP, 14.5 degree pressure angle, 3/8" thick. All gears have chamfered other edges on the teeth as per the originals. Gears included are: 60/63 teeth compound gear 42, 36, 33, 30, 27, 24 stud gears. The stud gear (upper most red gear in photos) meshes with the 60 tooth side of the compound gear. The 63 tooth side of the compound gear meshes with the standard 56 tooth screw gear on the input to the gearbox as per photos. I have included a diagram of the gear train. These gears run very quietly (compared to metal gears). I printed the compound gear with 6 top and 6 bottom layers, and 8 perimeters/walls and 50% infill using a cubic subdivision infill at 50% to provide as much rigidity as reasonably possible. Spur gears were printed with 6 top and 6 bottom layers, and 5 perimeters/walls. The number of perimeters/walls used was selected to ensure that all of the gear teeth were 100% solid and the 100% "fill" extended into a continuous ring within the rim of the gears to maximise tooth strength. If you make these, please post a make. For those who have tipped me a coffee, I offer back a huge thanks. Your contributions are very much appreciated. . For those who wish to, I thank you for appreciating the many hours of work that went into creating and testing these. Tips encourage designers to share their work.
Statistics
Likes
29
Downloads
0